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4272 lines
117 KiB
4272 lines
117 KiB
// SPDX-License-Identifier: GPL-2.0-or-later |
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/* |
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* Fast Userspace Mutexes (which I call "Futexes!"). |
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* (C) Rusty Russell, IBM 2002 |
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* |
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* Generalized futexes, futex requeueing, misc fixes by Ingo Molnar |
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* (C) Copyright 2003 Red Hat Inc, All Rights Reserved |
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* |
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* Removed page pinning, fix privately mapped COW pages and other cleanups |
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* (C) Copyright 2003, 2004 Jamie Lokier |
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* |
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* Robust futex support started by Ingo Molnar |
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* (C) Copyright 2006 Red Hat Inc, All Rights Reserved |
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* Thanks to Thomas Gleixner for suggestions, analysis and fixes. |
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* |
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* PI-futex support started by Ingo Molnar and Thomas Gleixner |
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* Copyright (C) 2006 Red Hat, Inc., Ingo Molnar <[email protected]> |
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* Copyright (C) 2006 Timesys Corp., Thomas Gleixner <[email protected]> |
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* |
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* PRIVATE futexes by Eric Dumazet |
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* Copyright (C) 2007 Eric Dumazet <[email protected]> |
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* |
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* Requeue-PI support by Darren Hart <[email protected]> |
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* Copyright (C) IBM Corporation, 2009 |
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* Thanks to Thomas Gleixner for conceptual design and careful reviews. |
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* |
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* Thanks to Ben LaHaise for yelling "hashed waitqueues" loudly |
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* enough at me, Linus for the original (flawed) idea, Matthew |
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* Kirkwood for proof-of-concept implementation. |
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* |
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* "The futexes are also cursed." |
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* "But they come in a choice of three flavours!" |
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*/ |
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#include <linux/compat.h> |
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#include <linux/jhash.h> |
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#include <linux/pagemap.h> |
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#include <linux/syscalls.h> |
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#include <linux/freezer.h> |
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#include <linux/memblock.h> |
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#include <linux/fault-inject.h> |
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#include <linux/time_namespace.h> |
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|
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#include <asm/futex.h> |
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|
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#include "locking/rtmutex_common.h" |
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|
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/* |
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* READ this before attempting to hack on futexes! |
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* |
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* Basic futex operation and ordering guarantees |
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* ============================================= |
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* |
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* The waiter reads the futex value in user space and calls |
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* futex_wait(). This function computes the hash bucket and acquires |
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* the hash bucket lock. After that it reads the futex user space value |
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* again and verifies that the data has not changed. If it has not changed |
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* it enqueues itself into the hash bucket, releases the hash bucket lock |
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* and schedules. |
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* |
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* The waker side modifies the user space value of the futex and calls |
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* futex_wake(). This function computes the hash bucket and acquires the |
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* hash bucket lock. Then it looks for waiters on that futex in the hash |
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* bucket and wakes them. |
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* |
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* In futex wake up scenarios where no tasks are blocked on a futex, taking |
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* the hb spinlock can be avoided and simply return. In order for this |
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* optimization to work, ordering guarantees must exist so that the waiter |
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* being added to the list is acknowledged when the list is concurrently being |
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* checked by the waker, avoiding scenarios like the following: |
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* |
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* CPU 0 CPU 1 |
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* val = *futex; |
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* sys_futex(WAIT, futex, val); |
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* futex_wait(futex, val); |
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* uval = *futex; |
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* *futex = newval; |
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* sys_futex(WAKE, futex); |
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* futex_wake(futex); |
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* if (queue_empty()) |
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* return; |
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* if (uval == val) |
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* lock(hash_bucket(futex)); |
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* queue(); |
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* unlock(hash_bucket(futex)); |
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* schedule(); |
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* |
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* This would cause the waiter on CPU 0 to wait forever because it |
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* missed the transition of the user space value from val to newval |
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* and the waker did not find the waiter in the hash bucket queue. |
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* |
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* The correct serialization ensures that a waiter either observes |
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* the changed user space value before blocking or is woken by a |
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* concurrent waker: |
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* |
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* CPU 0 CPU 1 |
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* val = *futex; |
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* sys_futex(WAIT, futex, val); |
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* futex_wait(futex, val); |
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* |
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* waiters++; (a) |
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* smp_mb(); (A) <-- paired with -. |
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* | |
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* lock(hash_bucket(futex)); | |
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* | |
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* uval = *futex; | |
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* | *futex = newval; |
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* | sys_futex(WAKE, futex); |
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* | futex_wake(futex); |
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* | |
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* `--------> smp_mb(); (B) |
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* if (uval == val) |
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* queue(); |
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* unlock(hash_bucket(futex)); |
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* schedule(); if (waiters) |
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* lock(hash_bucket(futex)); |
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* else wake_waiters(futex); |
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* waiters--; (b) unlock(hash_bucket(futex)); |
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* |
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* Where (A) orders the waiters increment and the futex value read through |
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* atomic operations (see hb_waiters_inc) and where (B) orders the write |
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* to futex and the waiters read (see hb_waiters_pending()). |
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* |
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* This yields the following case (where X:=waiters, Y:=futex): |
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* |
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* X = Y = 0 |
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* |
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* w[X]=1 w[Y]=1 |
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* MB MB |
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* r[Y]=y r[X]=x |
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* |
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* Which guarantees that x==0 && y==0 is impossible; which translates back into |
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* the guarantee that we cannot both miss the futex variable change and the |
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* enqueue. |
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* |
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* Note that a new waiter is accounted for in (a) even when it is possible that |
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* the wait call can return error, in which case we backtrack from it in (b). |
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* Refer to the comment in queue_lock(). |
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* |
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* Similarly, in order to account for waiters being requeued on another |
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* address we always increment the waiters for the destination bucket before |
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* acquiring the lock. It then decrements them again after releasing it - |
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* the code that actually moves the futex(es) between hash buckets (requeue_futex) |
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* will do the additional required waiter count housekeeping. This is done for |
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* double_lock_hb() and double_unlock_hb(), respectively. |
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*/ |
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#ifdef CONFIG_HAVE_FUTEX_CMPXCHG |
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#define futex_cmpxchg_enabled 1 |
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#else |
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static int __read_mostly futex_cmpxchg_enabled; |
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#endif |
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/* |
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* Futex flags used to encode options to functions and preserve them across |
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* restarts. |
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*/ |
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#ifdef CONFIG_MMU |
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# define FLAGS_SHARED 0x01 |
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#else |
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/* |
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* NOMMU does not have per process address space. Let the compiler optimize |
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* code away. |
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*/ |
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# define FLAGS_SHARED 0x00 |
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#endif |
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#define FLAGS_CLOCKRT 0x02 |
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#define FLAGS_HAS_TIMEOUT 0x04 |
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/* |
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* Priority Inheritance state: |
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*/ |
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struct futex_pi_state { |
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/* |
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* list of 'owned' pi_state instances - these have to be |
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* cleaned up in do_exit() if the task exits prematurely: |
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*/ |
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struct list_head list; |
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/* |
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* The PI object: |
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*/ |
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struct rt_mutex_base pi_mutex; |
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struct task_struct *owner; |
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refcount_t refcount; |
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union futex_key key; |
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} __randomize_layout; |
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/** |
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* struct futex_q - The hashed futex queue entry, one per waiting task |
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* @list: priority-sorted list of tasks waiting on this futex |
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* @task: the task waiting on the futex |
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* @lock_ptr: the hash bucket lock |
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* @key: the key the futex is hashed on |
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* @pi_state: optional priority inheritance state |
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* @rt_waiter: rt_waiter storage for use with requeue_pi |
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* @requeue_pi_key: the requeue_pi target futex key |
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* @bitset: bitset for the optional bitmasked wakeup |
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* @requeue_state: State field for futex_requeue_pi() |
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* @requeue_wait: RCU wait for futex_requeue_pi() (RT only) |
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* |
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* We use this hashed waitqueue, instead of a normal wait_queue_entry_t, so |
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* we can wake only the relevant ones (hashed queues may be shared). |
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* |
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* A futex_q has a woken state, just like tasks have TASK_RUNNING. |
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* It is considered woken when plist_node_empty(&q->list) || q->lock_ptr == 0. |
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* The order of wakeup is always to make the first condition true, then |
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* the second. |
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* |
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* PI futexes are typically woken before they are removed from the hash list via |
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* the rt_mutex code. See unqueue_me_pi(). |
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*/ |
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struct futex_q { |
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struct plist_node list; |
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struct task_struct *task; |
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spinlock_t *lock_ptr; |
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union futex_key key; |
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struct futex_pi_state *pi_state; |
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struct rt_mutex_waiter *rt_waiter; |
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union futex_key *requeue_pi_key; |
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u32 bitset; |
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atomic_t requeue_state; |
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#ifdef CONFIG_PREEMPT_RT |
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struct rcuwait requeue_wait; |
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#endif |
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} __randomize_layout; |
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/* |
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* On PREEMPT_RT, the hash bucket lock is a 'sleeping' spinlock with an |
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* underlying rtmutex. The task which is about to be requeued could have |
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* just woken up (timeout, signal). After the wake up the task has to |
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* acquire hash bucket lock, which is held by the requeue code. As a task |
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* can only be blocked on _ONE_ rtmutex at a time, the proxy lock blocking |
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* and the hash bucket lock blocking would collide and corrupt state. |
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* |
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* On !PREEMPT_RT this is not a problem and everything could be serialized |
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* on hash bucket lock, but aside of having the benefit of common code, |
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* this allows to avoid doing the requeue when the task is already on the |
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* way out and taking the hash bucket lock of the original uaddr1 when the |
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* requeue has been completed. |
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* |
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* The following state transitions are valid: |
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* |
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* On the waiter side: |
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* Q_REQUEUE_PI_NONE -> Q_REQUEUE_PI_IGNORE |
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* Q_REQUEUE_PI_IN_PROGRESS -> Q_REQUEUE_PI_WAIT |
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* |
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* On the requeue side: |
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* Q_REQUEUE_PI_NONE -> Q_REQUEUE_PI_INPROGRESS |
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* Q_REQUEUE_PI_IN_PROGRESS -> Q_REQUEUE_PI_DONE/LOCKED |
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* Q_REQUEUE_PI_IN_PROGRESS -> Q_REQUEUE_PI_NONE (requeue failed) |
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* Q_REQUEUE_PI_WAIT -> Q_REQUEUE_PI_DONE/LOCKED |
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* Q_REQUEUE_PI_WAIT -> Q_REQUEUE_PI_IGNORE (requeue failed) |
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* |
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* The requeue side ignores a waiter with state Q_REQUEUE_PI_IGNORE as this |
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* signals that the waiter is already on the way out. It also means that |
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* the waiter is still on the 'wait' futex, i.e. uaddr1. |
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* |
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* The waiter side signals early wakeup to the requeue side either through |
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* setting state to Q_REQUEUE_PI_IGNORE or to Q_REQUEUE_PI_WAIT depending |
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* on the current state. In case of Q_REQUEUE_PI_IGNORE it can immediately |
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* proceed to take the hash bucket lock of uaddr1. If it set state to WAIT, |
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* which means the wakeup is interleaving with a requeue in progress it has |
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* to wait for the requeue side to change the state. Either to DONE/LOCKED |
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* or to IGNORE. DONE/LOCKED means the waiter q is now on the uaddr2 futex |
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* and either blocked (DONE) or has acquired it (LOCKED). IGNORE is set by |
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* the requeue side when the requeue attempt failed via deadlock detection |
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* and therefore the waiter q is still on the uaddr1 futex. |
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*/ |
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enum { |
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Q_REQUEUE_PI_NONE = 0, |
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Q_REQUEUE_PI_IGNORE, |
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Q_REQUEUE_PI_IN_PROGRESS, |
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Q_REQUEUE_PI_WAIT, |
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Q_REQUEUE_PI_DONE, |
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Q_REQUEUE_PI_LOCKED, |
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}; |
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static const struct futex_q futex_q_init = { |
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/* list gets initialized in queue_me()*/ |
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.key = FUTEX_KEY_INIT, |
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.bitset = FUTEX_BITSET_MATCH_ANY, |
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.requeue_state = ATOMIC_INIT(Q_REQUEUE_PI_NONE), |
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}; |
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/* |
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* Hash buckets are shared by all the futex_keys that hash to the same |
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* location. Each key may have multiple futex_q structures, one for each task |
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* waiting on a futex. |
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*/ |
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struct futex_hash_bucket { |
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atomic_t waiters; |
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spinlock_t lock; |
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struct plist_head chain; |
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} ____cacheline_aligned_in_smp; |
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/* |
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* The base of the bucket array and its size are always used together |
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* (after initialization only in hash_futex()), so ensure that they |
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* reside in the same cacheline. |
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*/ |
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static struct { |
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struct futex_hash_bucket *queues; |
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unsigned long hashsize; |
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} __futex_data __read_mostly __aligned(2*sizeof(long)); |
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#define futex_queues (__futex_data.queues) |
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#define futex_hashsize (__futex_data.hashsize) |
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/* |
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* Fault injections for futexes. |
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*/ |
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#ifdef CONFIG_FAIL_FUTEX |
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static struct { |
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struct fault_attr attr; |
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bool ignore_private; |
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} fail_futex = { |
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.attr = FAULT_ATTR_INITIALIZER, |
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.ignore_private = false, |
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}; |
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static int __init setup_fail_futex(char *str) |
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{ |
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return setup_fault_attr(&fail_futex.attr, str); |
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} |
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__setup("fail_futex=", setup_fail_futex); |
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static bool should_fail_futex(bool fshared) |
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{ |
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if (fail_futex.ignore_private && !fshared) |
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return false; |
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return should_fail(&fail_futex.attr, 1); |
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} |
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#ifdef CONFIG_FAULT_INJECTION_DEBUG_FS |
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static int __init fail_futex_debugfs(void) |
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{ |
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umode_t mode = S_IFREG | S_IRUSR | S_IWUSR; |
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struct dentry *dir; |
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dir = fault_create_debugfs_attr("fail_futex", NULL, |
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&fail_futex.attr); |
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if (IS_ERR(dir)) |
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return PTR_ERR(dir); |
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debugfs_create_bool("ignore-private", mode, dir, |
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&fail_futex.ignore_private); |
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return 0; |
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} |
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late_initcall(fail_futex_debugfs); |
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#endif /* CONFIG_FAULT_INJECTION_DEBUG_FS */ |
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#else |
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static inline bool should_fail_futex(bool fshared) |
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{ |
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return false; |
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} |
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#endif /* CONFIG_FAIL_FUTEX */ |
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#ifdef CONFIG_COMPAT |
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static void compat_exit_robust_list(struct task_struct *curr); |
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#endif |
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/* |
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* Reflects a new waiter being added to the waitqueue. |
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*/ |
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static inline void hb_waiters_inc(struct futex_hash_bucket *hb) |
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{ |
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#ifdef CONFIG_SMP |
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atomic_inc(&hb->waiters); |
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/* |
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* Full barrier (A), see the ordering comment above. |
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*/ |
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smp_mb__after_atomic(); |
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#endif |
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} |
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/* |
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* Reflects a waiter being removed from the waitqueue by wakeup |
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* paths. |
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*/ |
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static inline void hb_waiters_dec(struct futex_hash_bucket *hb) |
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{ |
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#ifdef CONFIG_SMP |
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atomic_dec(&hb->waiters); |
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#endif |
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} |
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static inline int hb_waiters_pending(struct futex_hash_bucket *hb) |
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{ |
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#ifdef CONFIG_SMP |
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/* |
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* Full barrier (B), see the ordering comment above. |
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*/ |
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smp_mb(); |
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return atomic_read(&hb->waiters); |
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#else |
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return 1; |
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#endif |
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} |
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/** |
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* hash_futex - Return the hash bucket in the global hash |
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* @key: Pointer to the futex key for which the hash is calculated |
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* |
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* We hash on the keys returned from get_futex_key (see below) and return the |
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* corresponding hash bucket in the global hash. |
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*/ |
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static struct futex_hash_bucket *hash_futex(union futex_key *key) |
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{ |
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u32 hash = jhash2((u32 *)key, offsetof(typeof(*key), both.offset) / 4, |
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key->both.offset); |
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return &futex_queues[hash & (futex_hashsize - 1)]; |
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} |
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/** |
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* match_futex - Check whether two futex keys are equal |
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* @key1: Pointer to key1 |
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* @key2: Pointer to key2 |
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* |
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* Return 1 if two futex_keys are equal, 0 otherwise. |
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*/ |
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static inline int match_futex(union futex_key *key1, union futex_key *key2) |
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{ |
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return (key1 && key2 |
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&& key1->both.word == key2->both.word |
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&& key1->both.ptr == key2->both.ptr |
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&& key1->both.offset == key2->both.offset); |
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} |
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enum futex_access { |
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FUTEX_READ, |
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FUTEX_WRITE |
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}; |
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/** |
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* futex_setup_timer - set up the sleeping hrtimer. |
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* @time: ptr to the given timeout value |
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* @timeout: the hrtimer_sleeper structure to be set up |
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* @flags: futex flags |
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* @range_ns: optional range in ns |
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* |
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* Return: Initialized hrtimer_sleeper structure or NULL if no timeout |
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* value given |
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*/ |
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static inline struct hrtimer_sleeper * |
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futex_setup_timer(ktime_t *time, struct hrtimer_sleeper *timeout, |
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int flags, u64 range_ns) |
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{ |
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if (!time) |
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return NULL; |
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hrtimer_init_sleeper_on_stack(timeout, (flags & FLAGS_CLOCKRT) ? |
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CLOCK_REALTIME : CLOCK_MONOTONIC, |
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HRTIMER_MODE_ABS); |
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/* |
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* If range_ns is 0, calling hrtimer_set_expires_range_ns() is |
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* effectively the same as calling hrtimer_set_expires(). |
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*/ |
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hrtimer_set_expires_range_ns(&timeout->timer, *time, range_ns); |
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|
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return timeout; |
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} |
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|
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/* |
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* Generate a machine wide unique identifier for this inode. |
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* |
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* This relies on u64 not wrapping in the life-time of the machine; which with |
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* 1ns resolution means almost 585 years. |
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* |
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* This further relies on the fact that a well formed program will not unmap |
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* the file while it has a (shared) futex waiting on it. This mapping will have |
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* a file reference which pins the mount and inode. |
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* |
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* If for some reason an inode gets evicted and read back in again, it will get |
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* a new sequence number and will _NOT_ match, even though it is the exact same |
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* file. |
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* |
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* It is important that match_futex() will never have a false-positive, esp. |
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* for PI futexes that can mess up the state. The above argues that false-negatives |
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* are only possible for malformed programs. |
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*/ |
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static u64 get_inode_sequence_number(struct inode *inode) |
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{ |
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static atomic64_t i_seq; |
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u64 old; |
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|
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/* Does the inode already have a sequence number? */ |
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old = atomic64_read(&inode->i_sequence); |
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if (likely(old)) |
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return old; |
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|
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for (;;) { |
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u64 new = atomic64_add_return(1, &i_seq); |
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if (WARN_ON_ONCE(!new)) |
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continue; |
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old = atomic64_cmpxchg_relaxed(&inode->i_sequence, 0, new); |
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if (old) |
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return old; |
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return new; |
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} |
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} |
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|
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/** |
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* get_futex_key() - Get parameters which are the keys for a futex |
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* @uaddr: virtual address of the futex |
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* @fshared: false for a PROCESS_PRIVATE futex, true for PROCESS_SHARED |
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* @key: address where result is stored. |
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* @rw: mapping needs to be read/write (values: FUTEX_READ, |
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* FUTEX_WRITE) |
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* |
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* Return: a negative error code or 0 |
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* |
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* The key words are stored in @key on success. |
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* |
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* For shared mappings (when @fshared), the key is: |
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* |
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* ( inode->i_sequence, page->index, offset_within_page ) |
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* |
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* [ also see get_inode_sequence_number() ] |
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* |
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* For private mappings (or when !@fshared), the key is: |
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* |
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* ( current->mm, address, 0 ) |
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* |
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* This allows (cross process, where applicable) identification of the futex |
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* without keeping the page pinned for the duration of the FUTEX_WAIT. |
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* |
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* lock_page() might sleep, the caller should not hold a spinlock. |
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*/ |
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static int get_futex_key(u32 __user *uaddr, bool fshared, union futex_key *key, |
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enum futex_access rw) |
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{ |
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unsigned long address = (unsigned long)uaddr; |
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struct mm_struct *mm = current->mm; |
|
struct page *page, *tail; |
|
struct address_space *mapping; |
|
int err, ro = 0; |
|
|
|
/* |
|
* The futex address must be "naturally" aligned. |
|
*/ |
|
key->both.offset = address % PAGE_SIZE; |
|
if (unlikely((address % sizeof(u32)) != 0)) |
|
return -EINVAL; |
|
address -= key->both.offset; |
|
|
|
if (unlikely(!access_ok(uaddr, sizeof(u32)))) |
|
return -EFAULT; |
|
|
|
if (unlikely(should_fail_futex(fshared))) |
|
return -EFAULT; |
|
|
|
/* |
|
* PROCESS_PRIVATE futexes are fast. |
|
* As the mm cannot disappear under us and the 'key' only needs |
|
* virtual address, we dont even have to find the underlying vma. |
|
* Note : We do have to check 'uaddr' is a valid user address, |
|
* but access_ok() should be faster than find_vma() |
|
*/ |
|
if (!fshared) { |
|
key->private.mm = mm; |
|
key->private.address = address; |
|
return 0; |
|
} |
|
|
|
again: |
|
/* Ignore any VERIFY_READ mapping (futex common case) */ |
|
if (unlikely(should_fail_futex(true))) |
|
return -EFAULT; |
|
|
|
err = get_user_pages_fast(address, 1, FOLL_WRITE, &page); |
|
/* |
|
* If write access is not required (eg. FUTEX_WAIT), try |
|
* and get read-only access. |
|
*/ |
|
if (err == -EFAULT && rw == FUTEX_READ) { |
|
err = get_user_pages_fast(address, 1, 0, &page); |
|
ro = 1; |
|
} |
|
if (err < 0) |
|
return err; |
|
else |
|
err = 0; |
|
|
|
/* |
|
* The treatment of mapping from this point on is critical. The page |
|
* lock protects many things but in this context the page lock |
|
* stabilizes mapping, prevents inode freeing in the shared |
|
* file-backed region case and guards against movement to swap cache. |
|
* |
|
* Strictly speaking the page lock is not needed in all cases being |
|
* considered here and page lock forces unnecessarily serialization |
|
* From this point on, mapping will be re-verified if necessary and |
|
* page lock will be acquired only if it is unavoidable |
|
* |
|
* Mapping checks require the head page for any compound page so the |
|
* head page and mapping is looked up now. For anonymous pages, it |
|
* does not matter if the page splits in the future as the key is |
|
* based on the address. For filesystem-backed pages, the tail is |
|
* required as the index of the page determines the key. For |
|
* base pages, there is no tail page and tail == page. |
|
*/ |
|
tail = page; |
|
page = compound_head(page); |
|
mapping = READ_ONCE(page->mapping); |
|
|
|
/* |
|
* If page->mapping is NULL, then it cannot be a PageAnon |
|
* page; but it might be the ZERO_PAGE or in the gate area or |
|
* in a special mapping (all cases which we are happy to fail); |
|
* or it may have been a good file page when get_user_pages_fast |
|
* found it, but truncated or holepunched or subjected to |
|
* invalidate_complete_page2 before we got the page lock (also |
|
* cases which we are happy to fail). And we hold a reference, |
|
* so refcount care in invalidate_complete_page's remove_mapping |
|
* prevents drop_caches from setting mapping to NULL beneath us. |
|
* |
|
* The case we do have to guard against is when memory pressure made |
|
* shmem_writepage move it from filecache to swapcache beneath us: |
|
* an unlikely race, but we do need to retry for page->mapping. |
|
*/ |
|
if (unlikely(!mapping)) { |
|
int shmem_swizzled; |
|
|
|
/* |
|
* Page lock is required to identify which special case above |
|
* applies. If this is really a shmem page then the page lock |
|
* will prevent unexpected transitions. |
|
*/ |
|
lock_page(page); |
|
shmem_swizzled = PageSwapCache(page) || page->mapping; |
|
unlock_page(page); |
|
put_page(page); |
|
|
|
if (shmem_swizzled) |
|
goto again; |
|
|
|
return -EFAULT; |
|
} |
|
|
|
/* |
|
* Private mappings are handled in a simple way. |
|
* |
|
* If the futex key is stored on an anonymous page, then the associated |
|
* object is the mm which is implicitly pinned by the calling process. |
|
* |
|
* NOTE: When userspace waits on a MAP_SHARED mapping, even if |
|
* it's a read-only handle, it's expected that futexes attach to |
|
* the object not the particular process. |
|
*/ |
|
if (PageAnon(page)) { |
|
/* |
|
* A RO anonymous page will never change and thus doesn't make |
|
* sense for futex operations. |
|
*/ |
|
if (unlikely(should_fail_futex(true)) || ro) { |
|
err = -EFAULT; |
|
goto out; |
|
} |
|
|
|
key->both.offset |= FUT_OFF_MMSHARED; /* ref taken on mm */ |
|
key->private.mm = mm; |
|
key->private.address = address; |
|
|
|
} else { |
|
struct inode *inode; |
|
|
|
/* |
|
* The associated futex object in this case is the inode and |
|
* the page->mapping must be traversed. Ordinarily this should |
|
* be stabilised under page lock but it's not strictly |
|
* necessary in this case as we just want to pin the inode, not |
|
* update the radix tree or anything like that. |
|
* |
|
* The RCU read lock is taken as the inode is finally freed |
|
* under RCU. If the mapping still matches expectations then the |
|
* mapping->host can be safely accessed as being a valid inode. |
|
*/ |
|
rcu_read_lock(); |
|
|
|
if (READ_ONCE(page->mapping) != mapping) { |
|
rcu_read_unlock(); |
|
put_page(page); |
|
|
|
goto again; |
|
} |
|
|
|
inode = READ_ONCE(mapping->host); |
|
if (!inode) { |
|
rcu_read_unlock(); |
|
put_page(page); |
|
|
|
goto again; |
|
} |
|
|
|
key->both.offset |= FUT_OFF_INODE; /* inode-based key */ |
|
key->shared.i_seq = get_inode_sequence_number(inode); |
|
key->shared.pgoff = page_to_pgoff(tail); |
|
rcu_read_unlock(); |
|
} |
|
|
|
out: |
|
put_page(page); |
|
return err; |
|
} |
|
|
|
/** |
|
* fault_in_user_writeable() - Fault in user address and verify RW access |
|
* @uaddr: pointer to faulting user space address |
|
* |
|
* Slow path to fixup the fault we just took in the atomic write |
|
* access to @uaddr. |
|
* |
|
* We have no generic implementation of a non-destructive write to the |
|
* user address. We know that we faulted in the atomic pagefault |
|
* disabled section so we can as well avoid the #PF overhead by |
|
* calling get_user_pages() right away. |
|
*/ |
|
static int fault_in_user_writeable(u32 __user *uaddr) |
|
{ |
|
struct mm_struct *mm = current->mm; |
|
int ret; |
|
|
|
mmap_read_lock(mm); |
|
ret = fixup_user_fault(mm, (unsigned long)uaddr, |
|
FAULT_FLAG_WRITE, NULL); |
|
mmap_read_unlock(mm); |
|
|
|
return ret < 0 ? ret : 0; |
|
} |
|
|
|
/** |
|
* futex_top_waiter() - Return the highest priority waiter on a futex |
|
* @hb: the hash bucket the futex_q's reside in |
|
* @key: the futex key (to distinguish it from other futex futex_q's) |
|
* |
|
* Must be called with the hb lock held. |
|
*/ |
|
static struct futex_q *futex_top_waiter(struct futex_hash_bucket *hb, |
|
union futex_key *key) |
|
{ |
|
struct futex_q *this; |
|
|
|
plist_for_each_entry(this, &hb->chain, list) { |
|
if (match_futex(&this->key, key)) |
|
return this; |
|
} |
|
return NULL; |
|
} |
|
|
|
static int cmpxchg_futex_value_locked(u32 *curval, u32 __user *uaddr, |
|
u32 uval, u32 newval) |
|
{ |
|
int ret; |
|
|
|
pagefault_disable(); |
|
ret = futex_atomic_cmpxchg_inatomic(curval, uaddr, uval, newval); |
|
pagefault_enable(); |
|
|
|
return ret; |
|
} |
|
|
|
static int get_futex_value_locked(u32 *dest, u32 __user *from) |
|
{ |
|
int ret; |
|
|
|
pagefault_disable(); |
|
ret = __get_user(*dest, from); |
|
pagefault_enable(); |
|
|
|
return ret ? -EFAULT : 0; |
|
} |
|
|
|
|
|
/* |
|
* PI code: |
|
*/ |
|
static int refill_pi_state_cache(void) |
|
{ |
|
struct futex_pi_state *pi_state; |
|
|
|
if (likely(current->pi_state_cache)) |
|
return 0; |
|
|
|
pi_state = kzalloc(sizeof(*pi_state), GFP_KERNEL); |
|
|
|
if (!pi_state) |
|
return -ENOMEM; |
|
|
|
INIT_LIST_HEAD(&pi_state->list); |
|
/* pi_mutex gets initialized later */ |
|
pi_state->owner = NULL; |
|
refcount_set(&pi_state->refcount, 1); |
|
pi_state->key = FUTEX_KEY_INIT; |
|
|
|
current->pi_state_cache = pi_state; |
|
|
|
return 0; |
|
} |
|
|
|
static struct futex_pi_state *alloc_pi_state(void) |
|
{ |
|
struct futex_pi_state *pi_state = current->pi_state_cache; |
|
|
|
WARN_ON(!pi_state); |
|
current->pi_state_cache = NULL; |
|
|
|
return pi_state; |
|
} |
|
|
|
static void pi_state_update_owner(struct futex_pi_state *pi_state, |
|
struct task_struct *new_owner) |
|
{ |
|
struct task_struct *old_owner = pi_state->owner; |
|
|
|
lockdep_assert_held(&pi_state->pi_mutex.wait_lock); |
|
|
|
if (old_owner) { |
|
raw_spin_lock(&old_owner->pi_lock); |
|
WARN_ON(list_empty(&pi_state->list)); |
|
list_del_init(&pi_state->list); |
|
raw_spin_unlock(&old_owner->pi_lock); |
|
} |
|
|
|
if (new_owner) { |
|
raw_spin_lock(&new_owner->pi_lock); |
|
WARN_ON(!list_empty(&pi_state->list)); |
|
list_add(&pi_state->list, &new_owner->pi_state_list); |
|
pi_state->owner = new_owner; |
|
raw_spin_unlock(&new_owner->pi_lock); |
|
} |
|
} |
|
|
|
static void get_pi_state(struct futex_pi_state *pi_state) |
|
{ |
|
WARN_ON_ONCE(!refcount_inc_not_zero(&pi_state->refcount)); |
|
} |
|
|
|
/* |
|
* Drops a reference to the pi_state object and frees or caches it |
|
* when the last reference is gone. |
|
*/ |
|
static void put_pi_state(struct futex_pi_state *pi_state) |
|
{ |
|
if (!pi_state) |
|
return; |
|
|
|
if (!refcount_dec_and_test(&pi_state->refcount)) |
|
return; |
|
|
|
/* |
|
* If pi_state->owner is NULL, the owner is most probably dying |
|
* and has cleaned up the pi_state already |
|
*/ |
|
if (pi_state->owner) { |
|
unsigned long flags; |
|
|
|
raw_spin_lock_irqsave(&pi_state->pi_mutex.wait_lock, flags); |
|
pi_state_update_owner(pi_state, NULL); |
|
rt_mutex_proxy_unlock(&pi_state->pi_mutex); |
|
raw_spin_unlock_irqrestore(&pi_state->pi_mutex.wait_lock, flags); |
|
} |
|
|
|
if (current->pi_state_cache) { |
|
kfree(pi_state); |
|
} else { |
|
/* |
|
* pi_state->list is already empty. |
|
* clear pi_state->owner. |
|
* refcount is at 0 - put it back to 1. |
|
*/ |
|
pi_state->owner = NULL; |
|
refcount_set(&pi_state->refcount, 1); |
|
current->pi_state_cache = pi_state; |
|
} |
|
} |
|
|
|
#ifdef CONFIG_FUTEX_PI |
|
|
|
/* |
|
* This task is holding PI mutexes at exit time => bad. |
|
* Kernel cleans up PI-state, but userspace is likely hosed. |
|
* (Robust-futex cleanup is separate and might save the day for userspace.) |
|
*/ |
|
static void exit_pi_state_list(struct task_struct *curr) |
|
{ |
|
struct list_head *next, *head = &curr->pi_state_list; |
|
struct futex_pi_state *pi_state; |
|
struct futex_hash_bucket *hb; |
|
union futex_key key = FUTEX_KEY_INIT; |
|
|
|
if (!futex_cmpxchg_enabled) |
|
return; |
|
/* |
|
* We are a ZOMBIE and nobody can enqueue itself on |
|
* pi_state_list anymore, but we have to be careful |
|
* versus waiters unqueueing themselves: |
|
*/ |
|
raw_spin_lock_irq(&curr->pi_lock); |
|
while (!list_empty(head)) { |
|
next = head->next; |
|
pi_state = list_entry(next, struct futex_pi_state, list); |
|
key = pi_state->key; |
|
hb = hash_futex(&key); |
|
|
|
/* |
|
* We can race against put_pi_state() removing itself from the |
|
* list (a waiter going away). put_pi_state() will first |
|
* decrement the reference count and then modify the list, so |
|
* its possible to see the list entry but fail this reference |
|
* acquire. |
|
* |
|
* In that case; drop the locks to let put_pi_state() make |
|
* progress and retry the loop. |
|
*/ |
|
if (!refcount_inc_not_zero(&pi_state->refcount)) { |
|
raw_spin_unlock_irq(&curr->pi_lock); |
|
cpu_relax(); |
|
raw_spin_lock_irq(&curr->pi_lock); |
|
continue; |
|
} |
|
raw_spin_unlock_irq(&curr->pi_lock); |
|
|
|
spin_lock(&hb->lock); |
|
raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock); |
|
raw_spin_lock(&curr->pi_lock); |
|
/* |
|
* We dropped the pi-lock, so re-check whether this |
|
* task still owns the PI-state: |
|
*/ |
|
if (head->next != next) { |
|
/* retain curr->pi_lock for the loop invariant */ |
|
raw_spin_unlock(&pi_state->pi_mutex.wait_lock); |
|
spin_unlock(&hb->lock); |
|
put_pi_state(pi_state); |
|
continue; |
|
} |
|
|
|
WARN_ON(pi_state->owner != curr); |
|
WARN_ON(list_empty(&pi_state->list)); |
|
list_del_init(&pi_state->list); |
|
pi_state->owner = NULL; |
|
|
|
raw_spin_unlock(&curr->pi_lock); |
|
raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock); |
|
spin_unlock(&hb->lock); |
|
|
|
rt_mutex_futex_unlock(&pi_state->pi_mutex); |
|
put_pi_state(pi_state); |
|
|
|
raw_spin_lock_irq(&curr->pi_lock); |
|
} |
|
raw_spin_unlock_irq(&curr->pi_lock); |
|
} |
|
#else |
|
static inline void exit_pi_state_list(struct task_struct *curr) { } |
|
#endif |
|
|
|
/* |
|
* We need to check the following states: |
|
* |
|
* Waiter | pi_state | pi->owner | uTID | uODIED | ? |
|
* |
|
* [1] NULL | --- | --- | 0 | 0/1 | Valid |
|
* [2] NULL | --- | --- | >0 | 0/1 | Valid |
|
* |
|
* [3] Found | NULL | -- | Any | 0/1 | Invalid |
|
* |
|
* [4] Found | Found | NULL | 0 | 1 | Valid |
|
* [5] Found | Found | NULL | >0 | 1 | Invalid |
|
* |
|
* [6] Found | Found | task | 0 | 1 | Valid |
|
* |
|
* [7] Found | Found | NULL | Any | 0 | Invalid |
|
* |
|
* [8] Found | Found | task | ==taskTID | 0/1 | Valid |
|
* [9] Found | Found | task | 0 | 0 | Invalid |
|
* [10] Found | Found | task | !=taskTID | 0/1 | Invalid |
|
* |
|
* [1] Indicates that the kernel can acquire the futex atomically. We |
|
* came here due to a stale FUTEX_WAITERS/FUTEX_OWNER_DIED bit. |
|
* |
|
* [2] Valid, if TID does not belong to a kernel thread. If no matching |
|
* thread is found then it indicates that the owner TID has died. |
|
* |
|
* [3] Invalid. The waiter is queued on a non PI futex |
|
* |
|
* [4] Valid state after exit_robust_list(), which sets the user space |
|
* value to FUTEX_WAITERS | FUTEX_OWNER_DIED. |
|
* |
|
* [5] The user space value got manipulated between exit_robust_list() |
|
* and exit_pi_state_list() |
|
* |
|
* [6] Valid state after exit_pi_state_list() which sets the new owner in |
|
* the pi_state but cannot access the user space value. |
|
* |
|
* [7] pi_state->owner can only be NULL when the OWNER_DIED bit is set. |
|
* |
|
* [8] Owner and user space value match |
|
* |
|
* [9] There is no transient state which sets the user space TID to 0 |
|
* except exit_robust_list(), but this is indicated by the |
|
* FUTEX_OWNER_DIED bit. See [4] |
|
* |
|
* [10] There is no transient state which leaves owner and user space |
|
* TID out of sync. Except one error case where the kernel is denied |
|
* write access to the user address, see fixup_pi_state_owner(). |
|
* |
|
* |
|
* Serialization and lifetime rules: |
|
* |
|
* hb->lock: |
|
* |
|
* hb -> futex_q, relation |
|
* futex_q -> pi_state, relation |
|
* |
|
* (cannot be raw because hb can contain arbitrary amount |
|
* of futex_q's) |
|
* |
|
* pi_mutex->wait_lock: |
|
* |
|
* {uval, pi_state} |
|
* |
|
* (and pi_mutex 'obviously') |
|
* |
|
* p->pi_lock: |
|
* |
|
* p->pi_state_list -> pi_state->list, relation |
|
* pi_mutex->owner -> pi_state->owner, relation |
|
* |
|
* pi_state->refcount: |
|
* |
|
* pi_state lifetime |
|
* |
|
* |
|
* Lock order: |
|
* |
|
* hb->lock |
|
* pi_mutex->wait_lock |
|
* p->pi_lock |
|
* |
|
*/ |
|
|
|
/* |
|
* Validate that the existing waiter has a pi_state and sanity check |
|
* the pi_state against the user space value. If correct, attach to |
|
* it. |
|
*/ |
|
static int attach_to_pi_state(u32 __user *uaddr, u32 uval, |
|
struct futex_pi_state *pi_state, |
|
struct futex_pi_state **ps) |
|
{ |
|
pid_t pid = uval & FUTEX_TID_MASK; |
|
u32 uval2; |
|
int ret; |
|
|
|
/* |
|
* Userspace might have messed up non-PI and PI futexes [3] |
|
*/ |
|
if (unlikely(!pi_state)) |
|
return -EINVAL; |
|
|
|
/* |
|
* We get here with hb->lock held, and having found a |
|
* futex_top_waiter(). This means that futex_lock_pi() of said futex_q |
|
* has dropped the hb->lock in between queue_me() and unqueue_me_pi(), |
|
* which in turn means that futex_lock_pi() still has a reference on |
|
* our pi_state. |
|
* |
|
* The waiter holding a reference on @pi_state also protects against |
|
* the unlocked put_pi_state() in futex_unlock_pi(), futex_lock_pi() |
|
* and futex_wait_requeue_pi() as it cannot go to 0 and consequently |
|
* free pi_state before we can take a reference ourselves. |
|
*/ |
|
WARN_ON(!refcount_read(&pi_state->refcount)); |
|
|
|
/* |
|
* Now that we have a pi_state, we can acquire wait_lock |
|
* and do the state validation. |
|
*/ |
|
raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock); |
|
|
|
/* |
|
* Since {uval, pi_state} is serialized by wait_lock, and our current |
|
* uval was read without holding it, it can have changed. Verify it |
|
* still is what we expect it to be, otherwise retry the entire |
|
* operation. |
|
*/ |
|
if (get_futex_value_locked(&uval2, uaddr)) |
|
goto out_efault; |
|
|
|
if (uval != uval2) |
|
goto out_eagain; |
|
|
|
/* |
|
* Handle the owner died case: |
|
*/ |
|
if (uval & FUTEX_OWNER_DIED) { |
|
/* |
|
* exit_pi_state_list sets owner to NULL and wakes the |
|
* topmost waiter. The task which acquires the |
|
* pi_state->rt_mutex will fixup owner. |
|
*/ |
|
if (!pi_state->owner) { |
|
/* |
|
* No pi state owner, but the user space TID |
|
* is not 0. Inconsistent state. [5] |
|
*/ |
|
if (pid) |
|
goto out_einval; |
|
/* |
|
* Take a ref on the state and return success. [4] |
|
*/ |
|
goto out_attach; |
|
} |
|
|
|
/* |
|
* If TID is 0, then either the dying owner has not |
|
* yet executed exit_pi_state_list() or some waiter |
|
* acquired the rtmutex in the pi state, but did not |
|
* yet fixup the TID in user space. |
|
* |
|
* Take a ref on the state and return success. [6] |
|
*/ |
|
if (!pid) |
|
goto out_attach; |
|
} else { |
|
/* |
|
* If the owner died bit is not set, then the pi_state |
|
* must have an owner. [7] |
|
*/ |
|
if (!pi_state->owner) |
|
goto out_einval; |
|
} |
|
|
|
/* |
|
* Bail out if user space manipulated the futex value. If pi |
|
* state exists then the owner TID must be the same as the |
|
* user space TID. [9/10] |
|
*/ |
|
if (pid != task_pid_vnr(pi_state->owner)) |
|
goto out_einval; |
|
|
|
out_attach: |
|
get_pi_state(pi_state); |
|
raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock); |
|
*ps = pi_state; |
|
return 0; |
|
|
|
out_einval: |
|
ret = -EINVAL; |
|
goto out_error; |
|
|
|
out_eagain: |
|
ret = -EAGAIN; |
|
goto out_error; |
|
|
|
out_efault: |
|
ret = -EFAULT; |
|
goto out_error; |
|
|
|
out_error: |
|
raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock); |
|
return ret; |
|
} |
|
|
|
/** |
|
* wait_for_owner_exiting - Block until the owner has exited |
|
* @ret: owner's current futex lock status |
|
* @exiting: Pointer to the exiting task |
|
* |
|
* Caller must hold a refcount on @exiting. |
|
*/ |
|
static void wait_for_owner_exiting(int ret, struct task_struct *exiting) |
|
{ |
|
if (ret != -EBUSY) { |
|
WARN_ON_ONCE(exiting); |
|
return; |
|
} |
|
|
|
if (WARN_ON_ONCE(ret == -EBUSY && !exiting)) |
|
return; |
|
|
|
mutex_lock(&exiting->futex_exit_mutex); |
|
/* |
|
* No point in doing state checking here. If the waiter got here |
|
* while the task was in exec()->exec_futex_release() then it can |
|
* have any FUTEX_STATE_* value when the waiter has acquired the |
|
* mutex. OK, if running, EXITING or DEAD if it reached exit() |
|
* already. Highly unlikely and not a problem. Just one more round |
|
* through the futex maze. |
|
*/ |
|
mutex_unlock(&exiting->futex_exit_mutex); |
|
|
|
put_task_struct(exiting); |
|
} |
|
|
|
static int handle_exit_race(u32 __user *uaddr, u32 uval, |
|
struct task_struct *tsk) |
|
{ |
|
u32 uval2; |
|
|
|
/* |
|
* If the futex exit state is not yet FUTEX_STATE_DEAD, tell the |
|
* caller that the alleged owner is busy. |
|
*/ |
|
if (tsk && tsk->futex_state != FUTEX_STATE_DEAD) |
|
return -EBUSY; |
|
|
|
/* |
|
* Reread the user space value to handle the following situation: |
|
* |
|
* CPU0 CPU1 |
|
* |
|
* sys_exit() sys_futex() |
|
* do_exit() futex_lock_pi() |
|
* futex_lock_pi_atomic() |
|
* exit_signals(tsk) No waiters: |
|
* tsk->flags |= PF_EXITING; *uaddr == 0x00000PID |
|
* mm_release(tsk) Set waiter bit |
|
* exit_robust_list(tsk) { *uaddr = 0x80000PID; |
|
* Set owner died attach_to_pi_owner() { |
|
* *uaddr = 0xC0000000; tsk = get_task(PID); |
|
* } if (!tsk->flags & PF_EXITING) { |
|
* ... attach(); |
|
* tsk->futex_state = } else { |
|
* FUTEX_STATE_DEAD; if (tsk->futex_state != |
|
* FUTEX_STATE_DEAD) |
|
* return -EAGAIN; |
|
* return -ESRCH; <--- FAIL |
|
* } |
|
* |
|
* Returning ESRCH unconditionally is wrong here because the |
|
* user space value has been changed by the exiting task. |
|
* |
|
* The same logic applies to the case where the exiting task is |
|
* already gone. |
|
*/ |
|
if (get_futex_value_locked(&uval2, uaddr)) |
|
return -EFAULT; |
|
|
|
/* If the user space value has changed, try again. */ |
|
if (uval2 != uval) |
|
return -EAGAIN; |
|
|
|
/* |
|
* The exiting task did not have a robust list, the robust list was |
|
* corrupted or the user space value in *uaddr is simply bogus. |
|
* Give up and tell user space. |
|
*/ |
|
return -ESRCH; |
|
} |
|
|
|
static void __attach_to_pi_owner(struct task_struct *p, union futex_key *key, |
|
struct futex_pi_state **ps) |
|
{ |
|
/* |
|
* No existing pi state. First waiter. [2] |
|
* |
|
* This creates pi_state, we have hb->lock held, this means nothing can |
|
* observe this state, wait_lock is irrelevant. |
|
*/ |
|
struct futex_pi_state *pi_state = alloc_pi_state(); |
|
|
|
/* |
|
* Initialize the pi_mutex in locked state and make @p |
|
* the owner of it: |
|
*/ |
|
rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p); |
|
|
|
/* Store the key for possible exit cleanups: */ |
|
pi_state->key = *key; |
|
|
|
WARN_ON(!list_empty(&pi_state->list)); |
|
list_add(&pi_state->list, &p->pi_state_list); |
|
/* |
|
* Assignment without holding pi_state->pi_mutex.wait_lock is safe |
|
* because there is no concurrency as the object is not published yet. |
|
*/ |
|
pi_state->owner = p; |
|
|
|
*ps = pi_state; |
|
} |
|
/* |
|
* Lookup the task for the TID provided from user space and attach to |
|
* it after doing proper sanity checks. |
|
*/ |
|
static int attach_to_pi_owner(u32 __user *uaddr, u32 uval, union futex_key *key, |
|
struct futex_pi_state **ps, |
|
struct task_struct **exiting) |
|
{ |
|
pid_t pid = uval & FUTEX_TID_MASK; |
|
struct task_struct *p; |
|
|
|
/* |
|
* We are the first waiter - try to look up the real owner and attach |
|
* the new pi_state to it, but bail out when TID = 0 [1] |
|
* |
|
* The !pid check is paranoid. None of the call sites should end up |
|
* with pid == 0, but better safe than sorry. Let the caller retry |
|
*/ |
|
if (!pid) |
|
return -EAGAIN; |
|
p = find_get_task_by_vpid(pid); |
|
if (!p) |
|
return handle_exit_race(uaddr, uval, NULL); |
|
|
|
if (unlikely(p->flags & PF_KTHREAD)) { |
|
put_task_struct(p); |
|
return -EPERM; |
|
} |
|
|
|
/* |
|
* We need to look at the task state to figure out, whether the |
|
* task is exiting. To protect against the change of the task state |
|
* in futex_exit_release(), we do this protected by p->pi_lock: |
|
*/ |
|
raw_spin_lock_irq(&p->pi_lock); |
|
if (unlikely(p->futex_state != FUTEX_STATE_OK)) { |
|
/* |
|
* The task is on the way out. When the futex state is |
|
* FUTEX_STATE_DEAD, we know that the task has finished |
|
* the cleanup: |
|
*/ |
|
int ret = handle_exit_race(uaddr, uval, p); |
|
|
|
raw_spin_unlock_irq(&p->pi_lock); |
|
/* |
|
* If the owner task is between FUTEX_STATE_EXITING and |
|
* FUTEX_STATE_DEAD then store the task pointer and keep |
|
* the reference on the task struct. The calling code will |
|
* drop all locks, wait for the task to reach |
|
* FUTEX_STATE_DEAD and then drop the refcount. This is |
|
* required to prevent a live lock when the current task |
|
* preempted the exiting task between the two states. |
|
*/ |
|
if (ret == -EBUSY) |
|
*exiting = p; |
|
else |
|
put_task_struct(p); |
|
return ret; |
|
} |
|
|
|
__attach_to_pi_owner(p, key, ps); |
|
raw_spin_unlock_irq(&p->pi_lock); |
|
|
|
put_task_struct(p); |
|
|
|
return 0; |
|
} |
|
|
|
static int lock_pi_update_atomic(u32 __user *uaddr, u32 uval, u32 newval) |
|
{ |
|
int err; |
|
u32 curval; |
|
|
|
if (unlikely(should_fail_futex(true))) |
|
return -EFAULT; |
|
|
|
err = cmpxchg_futex_value_locked(&curval, uaddr, uval, newval); |
|
if (unlikely(err)) |
|
return err; |
|
|
|
/* If user space value changed, let the caller retry */ |
|
return curval != uval ? -EAGAIN : 0; |
|
} |
|
|
|
/** |
|
* futex_lock_pi_atomic() - Atomic work required to acquire a pi aware futex |
|
* @uaddr: the pi futex user address |
|
* @hb: the pi futex hash bucket |
|
* @key: the futex key associated with uaddr and hb |
|
* @ps: the pi_state pointer where we store the result of the |
|
* lookup |
|
* @task: the task to perform the atomic lock work for. This will |
|
* be "current" except in the case of requeue pi. |
|
* @exiting: Pointer to store the task pointer of the owner task |
|
* which is in the middle of exiting |
|
* @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0) |
|
* |
|
* Return: |
|
* - 0 - ready to wait; |
|
* - 1 - acquired the lock; |
|
* - <0 - error |
|
* |
|
* The hb->lock must be held by the caller. |
|
* |
|
* @exiting is only set when the return value is -EBUSY. If so, this holds |
|
* a refcount on the exiting task on return and the caller needs to drop it |
|
* after waiting for the exit to complete. |
|
*/ |
|
static int futex_lock_pi_atomic(u32 __user *uaddr, struct futex_hash_bucket *hb, |
|
union futex_key *key, |
|
struct futex_pi_state **ps, |
|
struct task_struct *task, |
|
struct task_struct **exiting, |
|
int set_waiters) |
|
{ |
|
u32 uval, newval, vpid = task_pid_vnr(task); |
|
struct futex_q *top_waiter; |
|
int ret; |
|
|
|
/* |
|
* Read the user space value first so we can validate a few |
|
* things before proceeding further. |
|
*/ |
|
if (get_futex_value_locked(&uval, uaddr)) |
|
return -EFAULT; |
|
|
|
if (unlikely(should_fail_futex(true))) |
|
return -EFAULT; |
|
|
|
/* |
|
* Detect deadlocks. |
|
*/ |
|
if ((unlikely((uval & FUTEX_TID_MASK) == vpid))) |
|
return -EDEADLK; |
|
|
|
if ((unlikely(should_fail_futex(true)))) |
|
return -EDEADLK; |
|
|
|
/* |
|
* Lookup existing state first. If it exists, try to attach to |
|
* its pi_state. |
|
*/ |
|
top_waiter = futex_top_waiter(hb, key); |
|
if (top_waiter) |
|
return attach_to_pi_state(uaddr, uval, top_waiter->pi_state, ps); |
|
|
|
/* |
|
* No waiter and user TID is 0. We are here because the |
|
* waiters or the owner died bit is set or called from |
|
* requeue_cmp_pi or for whatever reason something took the |
|
* syscall. |
|
*/ |
|
if (!(uval & FUTEX_TID_MASK)) { |
|
/* |
|
* We take over the futex. No other waiters and the user space |
|
* TID is 0. We preserve the owner died bit. |
|
*/ |
|
newval = uval & FUTEX_OWNER_DIED; |
|
newval |= vpid; |
|
|
|
/* The futex requeue_pi code can enforce the waiters bit */ |
|
if (set_waiters) |
|
newval |= FUTEX_WAITERS; |
|
|
|
ret = lock_pi_update_atomic(uaddr, uval, newval); |
|
if (ret) |
|
return ret; |
|
|
|
/* |
|
* If the waiter bit was requested the caller also needs PI |
|
* state attached to the new owner of the user space futex. |
|
* |
|
* @task is guaranteed to be alive and it cannot be exiting |
|
* because it is either sleeping or waiting in |
|
* futex_requeue_pi_wakeup_sync(). |
|
* |
|
* No need to do the full attach_to_pi_owner() exercise |
|
* because @task is known and valid. |
|
*/ |
|
if (set_waiters) { |
|
raw_spin_lock_irq(&task->pi_lock); |
|
__attach_to_pi_owner(task, key, ps); |
|
raw_spin_unlock_irq(&task->pi_lock); |
|
} |
|
return 1; |
|
} |
|
|
|
/* |
|
* First waiter. Set the waiters bit before attaching ourself to |
|
* the owner. If owner tries to unlock, it will be forced into |
|
* the kernel and blocked on hb->lock. |
|
*/ |
|
newval = uval | FUTEX_WAITERS; |
|
ret = lock_pi_update_atomic(uaddr, uval, newval); |
|
if (ret) |
|
return ret; |
|
/* |
|
* If the update of the user space value succeeded, we try to |
|
* attach to the owner. If that fails, no harm done, we only |
|
* set the FUTEX_WAITERS bit in the user space variable. |
|
*/ |
|
return attach_to_pi_owner(uaddr, newval, key, ps, exiting); |
|
} |
|
|
|
/** |
|
* __unqueue_futex() - Remove the futex_q from its futex_hash_bucket |
|
* @q: The futex_q to unqueue |
|
* |
|
* The q->lock_ptr must not be NULL and must be held by the caller. |
|
*/ |
|
static void __unqueue_futex(struct futex_q *q) |
|
{ |
|
struct futex_hash_bucket *hb; |
|
|
|
if (WARN_ON_SMP(!q->lock_ptr) || WARN_ON(plist_node_empty(&q->list))) |
|
return; |
|
lockdep_assert_held(q->lock_ptr); |
|
|
|
hb = container_of(q->lock_ptr, struct futex_hash_bucket, lock); |
|
plist_del(&q->list, &hb->chain); |
|
hb_waiters_dec(hb); |
|
} |
|
|
|
/* |
|
* The hash bucket lock must be held when this is called. |
|
* Afterwards, the futex_q must not be accessed. Callers |
|
* must ensure to later call wake_up_q() for the actual |
|
* wakeups to occur. |
|
*/ |
|
static void mark_wake_futex(struct wake_q_head *wake_q, struct futex_q *q) |
|
{ |
|
struct task_struct *p = q->task; |
|
|
|
if (WARN(q->pi_state || q->rt_waiter, "refusing to wake PI futex\n")) |
|
return; |
|
|
|
get_task_struct(p); |
|
__unqueue_futex(q); |
|
/* |
|
* The waiting task can free the futex_q as soon as q->lock_ptr = NULL |
|
* is written, without taking any locks. This is possible in the event |
|
* of a spurious wakeup, for example. A memory barrier is required here |
|
* to prevent the following store to lock_ptr from getting ahead of the |
|
* plist_del in __unqueue_futex(). |
|
*/ |
|
smp_store_release(&q->lock_ptr, NULL); |
|
|
|
/* |
|
* Queue the task for later wakeup for after we've released |
|
* the hb->lock. |
|
*/ |
|
wake_q_add_safe(wake_q, p); |
|
} |
|
|
|
/* |
|
* Caller must hold a reference on @pi_state. |
|
*/ |
|
static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_pi_state *pi_state) |
|
{ |
|
struct rt_mutex_waiter *top_waiter; |
|
struct task_struct *new_owner; |
|
bool postunlock = false; |
|
DEFINE_RT_WAKE_Q(wqh); |
|
u32 curval, newval; |
|
int ret = 0; |
|
|
|
top_waiter = rt_mutex_top_waiter(&pi_state->pi_mutex); |
|
if (WARN_ON_ONCE(!top_waiter)) { |
|
/* |
|
* As per the comment in futex_unlock_pi() this should not happen. |
|
* |
|
* When this happens, give up our locks and try again, giving |
|
* the futex_lock_pi() instance time to complete, either by |
|
* waiting on the rtmutex or removing itself from the futex |
|
* queue. |
|
*/ |
|
ret = -EAGAIN; |
|
goto out_unlock; |
|
} |
|
|
|
new_owner = top_waiter->task; |
|
|
|
/* |
|
* We pass it to the next owner. The WAITERS bit is always kept |
|
* enabled while there is PI state around. We cleanup the owner |
|
* died bit, because we are the owner. |
|
*/ |
|
newval = FUTEX_WAITERS | task_pid_vnr(new_owner); |
|
|
|
if (unlikely(should_fail_futex(true))) { |
|
ret = -EFAULT; |
|
goto out_unlock; |
|
} |
|
|
|
ret = cmpxchg_futex_value_locked(&curval, uaddr, uval, newval); |
|
if (!ret && (curval != uval)) { |
|
/* |
|
* If a unconditional UNLOCK_PI operation (user space did not |
|
* try the TID->0 transition) raced with a waiter setting the |
|
* FUTEX_WAITERS flag between get_user() and locking the hash |
|
* bucket lock, retry the operation. |
|
*/ |
|
if ((FUTEX_TID_MASK & curval) == uval) |
|
ret = -EAGAIN; |
|
else |
|
ret = -EINVAL; |
|
} |
|
|
|
if (!ret) { |
|
/* |
|
* This is a point of no return; once we modified the uval |
|
* there is no going back and subsequent operations must |
|
* not fail. |
|
*/ |
|
pi_state_update_owner(pi_state, new_owner); |
|
postunlock = __rt_mutex_futex_unlock(&pi_state->pi_mutex, &wqh); |
|
} |
|
|
|
out_unlock: |
|
raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock); |
|
|
|
if (postunlock) |
|
rt_mutex_postunlock(&wqh); |
|
|
|
return ret; |
|
} |
|
|
|
/* |
|
* Express the locking dependencies for lockdep: |
|
*/ |
|
static inline void |
|
double_lock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2) |
|
{ |
|
if (hb1 <= hb2) { |
|
spin_lock(&hb1->lock); |
|
if (hb1 < hb2) |
|
spin_lock_nested(&hb2->lock, SINGLE_DEPTH_NESTING); |
|
} else { /* hb1 > hb2 */ |
|
spin_lock(&hb2->lock); |
|
spin_lock_nested(&hb1->lock, SINGLE_DEPTH_NESTING); |
|
} |
|
} |
|
|
|
static inline void |
|
double_unlock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2) |
|
{ |
|
spin_unlock(&hb1->lock); |
|
if (hb1 != hb2) |
|
spin_unlock(&hb2->lock); |
|
} |
|
|
|
/* |
|
* Wake up waiters matching bitset queued on this futex (uaddr). |
|
*/ |
|
static int |
|
futex_wake(u32 __user *uaddr, unsigned int flags, int nr_wake, u32 bitset) |
|
{ |
|
struct futex_hash_bucket *hb; |
|
struct futex_q *this, *next; |
|
union futex_key key = FUTEX_KEY_INIT; |
|
int ret; |
|
DEFINE_WAKE_Q(wake_q); |
|
|
|
if (!bitset) |
|
return -EINVAL; |
|
|
|
ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, FUTEX_READ); |
|
if (unlikely(ret != 0)) |
|
return ret; |
|
|
|
hb = hash_futex(&key); |
|
|
|
/* Make sure we really have tasks to wakeup */ |
|
if (!hb_waiters_pending(hb)) |
|
return ret; |
|
|
|
spin_lock(&hb->lock); |
|
|
|
plist_for_each_entry_safe(this, next, &hb->chain, list) { |
|
if (match_futex (&this->key, &key)) { |
|
if (this->pi_state || this->rt_waiter) { |
|
ret = -EINVAL; |
|
break; |
|
} |
|
|
|
/* Check if one of the bits is set in both bitsets */ |
|
if (!(this->bitset & bitset)) |
|
continue; |
|
|
|
mark_wake_futex(&wake_q, this); |
|
if (++ret >= nr_wake) |
|
break; |
|
} |
|
} |
|
|
|
spin_unlock(&hb->lock); |
|
wake_up_q(&wake_q); |
|
return ret; |
|
} |
|
|
|
static int futex_atomic_op_inuser(unsigned int encoded_op, u32 __user *uaddr) |
|
{ |
|
unsigned int op = (encoded_op & 0x70000000) >> 28; |
|
unsigned int cmp = (encoded_op & 0x0f000000) >> 24; |
|
int oparg = sign_extend32((encoded_op & 0x00fff000) >> 12, 11); |
|
int cmparg = sign_extend32(encoded_op & 0x00000fff, 11); |
|
int oldval, ret; |
|
|
|
if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28)) { |
|
if (oparg < 0 || oparg > 31) { |
|
char comm[sizeof(current->comm)]; |
|
/* |
|
* kill this print and return -EINVAL when userspace |
|
* is sane again |
|
*/ |
|
pr_info_ratelimited("futex_wake_op: %s tries to shift op by %d; fix this program\n", |
|
get_task_comm(comm, current), oparg); |
|
oparg &= 31; |
|
} |
|
oparg = 1 << oparg; |
|
} |
|
|
|
pagefault_disable(); |
|
ret = arch_futex_atomic_op_inuser(op, oparg, &oldval, uaddr); |
|
pagefault_enable(); |
|
if (ret) |
|
return ret; |
|
|
|
switch (cmp) { |
|
case FUTEX_OP_CMP_EQ: |
|
return oldval == cmparg; |
|
case FUTEX_OP_CMP_NE: |
|
return oldval != cmparg; |
|
case FUTEX_OP_CMP_LT: |
|
return oldval < cmparg; |
|
case FUTEX_OP_CMP_GE: |
|
return oldval >= cmparg; |
|
case FUTEX_OP_CMP_LE: |
|
return oldval <= cmparg; |
|
case FUTEX_OP_CMP_GT: |
|
return oldval > cmparg; |
|
default: |
|
return -ENOSYS; |
|
} |
|
} |
|
|
|
/* |
|
* Wake up all waiters hashed on the physical page that is mapped |
|
* to this virtual address: |
|
*/ |
|
static int |
|
futex_wake_op(u32 __user *uaddr1, unsigned int flags, u32 __user *uaddr2, |
|
int nr_wake, int nr_wake2, int op) |
|
{ |
|
union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT; |
|
struct futex_hash_bucket *hb1, *hb2; |
|
struct futex_q *this, *next; |
|
int ret, op_ret; |
|
DEFINE_WAKE_Q(wake_q); |
|
|
|
retry: |
|
ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, FUTEX_READ); |
|
if (unlikely(ret != 0)) |
|
return ret; |
|
ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, FUTEX_WRITE); |
|
if (unlikely(ret != 0)) |
|
return ret; |
|
|
|
hb1 = hash_futex(&key1); |
|
hb2 = hash_futex(&key2); |
|
|
|
retry_private: |
|
double_lock_hb(hb1, hb2); |
|
op_ret = futex_atomic_op_inuser(op, uaddr2); |
|
if (unlikely(op_ret < 0)) { |
|
double_unlock_hb(hb1, hb2); |
|
|
|
if (!IS_ENABLED(CONFIG_MMU) || |
|
unlikely(op_ret != -EFAULT && op_ret != -EAGAIN)) { |
|
/* |
|
* we don't get EFAULT from MMU faults if we don't have |
|
* an MMU, but we might get them from range checking |
|
*/ |
|
ret = op_ret; |
|
return ret; |
|
} |
|
|
|
if (op_ret == -EFAULT) { |
|
ret = fault_in_user_writeable(uaddr2); |
|
if (ret) |
|
return ret; |
|
} |
|
|
|
cond_resched(); |
|
if (!(flags & FLAGS_SHARED)) |
|
goto retry_private; |
|
goto retry; |
|
} |
|
|
|
plist_for_each_entry_safe(this, next, &hb1->chain, list) { |
|
if (match_futex (&this->key, &key1)) { |
|
if (this->pi_state || this->rt_waiter) { |
|
ret = -EINVAL; |
|
goto out_unlock; |
|
} |
|
mark_wake_futex(&wake_q, this); |
|
if (++ret >= nr_wake) |
|
break; |
|
} |
|
} |
|
|
|
if (op_ret > 0) { |
|
op_ret = 0; |
|
plist_for_each_entry_safe(this, next, &hb2->chain, list) { |
|
if (match_futex (&this->key, &key2)) { |
|
if (this->pi_state || this->rt_waiter) { |
|
ret = -EINVAL; |
|
goto out_unlock; |
|
} |
|
mark_wake_futex(&wake_q, this); |
|
if (++op_ret >= nr_wake2) |
|
break; |
|
} |
|
} |
|
ret += op_ret; |
|
} |
|
|
|
out_unlock: |
|
double_unlock_hb(hb1, hb2); |
|
wake_up_q(&wake_q); |
|
return ret; |
|
} |
|
|
|
/** |
|
* requeue_futex() - Requeue a futex_q from one hb to another |
|
* @q: the futex_q to requeue |
|
* @hb1: the source hash_bucket |
|
* @hb2: the target hash_bucket |
|
* @key2: the new key for the requeued futex_q |
|
*/ |
|
static inline |
|
void requeue_futex(struct futex_q *q, struct futex_hash_bucket *hb1, |
|
struct futex_hash_bucket *hb2, union futex_key *key2) |
|
{ |
|
|
|
/* |
|
* If key1 and key2 hash to the same bucket, no need to |
|
* requeue. |
|
*/ |
|
if (likely(&hb1->chain != &hb2->chain)) { |
|
plist_del(&q->list, &hb1->chain); |
|
hb_waiters_dec(hb1); |
|
hb_waiters_inc(hb2); |
|
plist_add(&q->list, &hb2->chain); |
|
q->lock_ptr = &hb2->lock; |
|
} |
|
q->key = *key2; |
|
} |
|
|
|
static inline bool futex_requeue_pi_prepare(struct futex_q *q, |
|
struct futex_pi_state *pi_state) |
|
{ |
|
int old, new; |
|
|
|
/* |
|
* Set state to Q_REQUEUE_PI_IN_PROGRESS unless an early wakeup has |
|
* already set Q_REQUEUE_PI_IGNORE to signal that requeue should |
|
* ignore the waiter. |
|
*/ |
|
old = atomic_read_acquire(&q->requeue_state); |
|
do { |
|
if (old == Q_REQUEUE_PI_IGNORE) |
|
return false; |
|
|
|
/* |
|
* futex_proxy_trylock_atomic() might have set it to |
|
* IN_PROGRESS and a interleaved early wake to WAIT. |
|
* |
|
* It was considered to have an extra state for that |
|
* trylock, but that would just add more conditionals |
|
* all over the place for a dubious value. |
|
*/ |
|
if (old != Q_REQUEUE_PI_NONE) |
|
break; |
|
|
|
new = Q_REQUEUE_PI_IN_PROGRESS; |
|
} while (!atomic_try_cmpxchg(&q->requeue_state, &old, new)); |
|
|
|
q->pi_state = pi_state; |
|
return true; |
|
} |
|
|
|
static inline void futex_requeue_pi_complete(struct futex_q *q, int locked) |
|
{ |
|
int old, new; |
|
|
|
old = atomic_read_acquire(&q->requeue_state); |
|
do { |
|
if (old == Q_REQUEUE_PI_IGNORE) |
|
return; |
|
|
|
if (locked >= 0) { |
|
/* Requeue succeeded. Set DONE or LOCKED */ |
|
WARN_ON_ONCE(old != Q_REQUEUE_PI_IN_PROGRESS && |
|
old != Q_REQUEUE_PI_WAIT); |
|
new = Q_REQUEUE_PI_DONE + locked; |
|
} else if (old == Q_REQUEUE_PI_IN_PROGRESS) { |
|
/* Deadlock, no early wakeup interleave */ |
|
new = Q_REQUEUE_PI_NONE; |
|
} else { |
|
/* Deadlock, early wakeup interleave. */ |
|
WARN_ON_ONCE(old != Q_REQUEUE_PI_WAIT); |
|
new = Q_REQUEUE_PI_IGNORE; |
|
} |
|
} while (!atomic_try_cmpxchg(&q->requeue_state, &old, new)); |
|
|
|
#ifdef CONFIG_PREEMPT_RT |
|
/* If the waiter interleaved with the requeue let it know */ |
|
if (unlikely(old == Q_REQUEUE_PI_WAIT)) |
|
rcuwait_wake_up(&q->requeue_wait); |
|
#endif |
|
} |
|
|
|
static inline int futex_requeue_pi_wakeup_sync(struct futex_q *q) |
|
{ |
|
int old, new; |
|
|
|
old = atomic_read_acquire(&q->requeue_state); |
|
do { |
|
/* Is requeue done already? */ |
|
if (old >= Q_REQUEUE_PI_DONE) |
|
return old; |
|
|
|
/* |
|
* If not done, then tell the requeue code to either ignore |
|
* the waiter or to wake it up once the requeue is done. |
|
*/ |
|
new = Q_REQUEUE_PI_WAIT; |
|
if (old == Q_REQUEUE_PI_NONE) |
|
new = Q_REQUEUE_PI_IGNORE; |
|
} while (!atomic_try_cmpxchg(&q->requeue_state, &old, new)); |
|
|
|
/* If the requeue was in progress, wait for it to complete */ |
|
if (old == Q_REQUEUE_PI_IN_PROGRESS) { |
|
#ifdef CONFIG_PREEMPT_RT |
|
rcuwait_wait_event(&q->requeue_wait, |
|
atomic_read(&q->requeue_state) != Q_REQUEUE_PI_WAIT, |
|
TASK_UNINTERRUPTIBLE); |
|
#else |
|
(void)atomic_cond_read_relaxed(&q->requeue_state, VAL != Q_REQUEUE_PI_WAIT); |
|
#endif |
|
} |
|
|
|
/* |
|
* Requeue is now either prohibited or complete. Reread state |
|
* because during the wait above it might have changed. Nothing |
|
* will modify q->requeue_state after this point. |
|
*/ |
|
return atomic_read(&q->requeue_state); |
|
} |
|
|
|
/** |
|
* requeue_pi_wake_futex() - Wake a task that acquired the lock during requeue |
|
* @q: the futex_q |
|
* @key: the key of the requeue target futex |
|
* @hb: the hash_bucket of the requeue target futex |
|
* |
|
* During futex_requeue, with requeue_pi=1, it is possible to acquire the |
|
* target futex if it is uncontended or via a lock steal. |
|
* |
|
* 1) Set @q::key to the requeue target futex key so the waiter can detect |
|
* the wakeup on the right futex. |
|
* |
|
* 2) Dequeue @q from the hash bucket. |
|
* |
|
* 3) Set @q::rt_waiter to NULL so the woken up task can detect atomic lock |
|
* acquisition. |
|
* |
|
* 4) Set the q->lock_ptr to the requeue target hb->lock for the case that |
|
* the waiter has to fixup the pi state. |
|
* |
|
* 5) Complete the requeue state so the waiter can make progress. After |
|
* this point the waiter task can return from the syscall immediately in |
|
* case that the pi state does not have to be fixed up. |
|
* |
|
* 6) Wake the waiter task. |
|
* |
|
* Must be called with both q->lock_ptr and hb->lock held. |
|
*/ |
|
static inline |
|
void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key, |
|
struct futex_hash_bucket *hb) |
|
{ |
|
q->key = *key; |
|
|
|
__unqueue_futex(q); |
|
|
|
WARN_ON(!q->rt_waiter); |
|
q->rt_waiter = NULL; |
|
|
|
q->lock_ptr = &hb->lock; |
|
|
|
/* Signal locked state to the waiter */ |
|
futex_requeue_pi_complete(q, 1); |
|
wake_up_state(q->task, TASK_NORMAL); |
|
} |
|
|
|
/** |
|
* futex_proxy_trylock_atomic() - Attempt an atomic lock for the top waiter |
|
* @pifutex: the user address of the to futex |
|
* @hb1: the from futex hash bucket, must be locked by the caller |
|
* @hb2: the to futex hash bucket, must be locked by the caller |
|
* @key1: the from futex key |
|
* @key2: the to futex key |
|
* @ps: address to store the pi_state pointer |
|
* @exiting: Pointer to store the task pointer of the owner task |
|
* which is in the middle of exiting |
|
* @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0) |
|
* |
|
* Try and get the lock on behalf of the top waiter if we can do it atomically. |
|
* Wake the top waiter if we succeed. If the caller specified set_waiters, |
|
* then direct futex_lock_pi_atomic() to force setting the FUTEX_WAITERS bit. |
|
* hb1 and hb2 must be held by the caller. |
|
* |
|
* @exiting is only set when the return value is -EBUSY. If so, this holds |
|
* a refcount on the exiting task on return and the caller needs to drop it |
|
* after waiting for the exit to complete. |
|
* |
|
* Return: |
|
* - 0 - failed to acquire the lock atomically; |
|
* - >0 - acquired the lock, return value is vpid of the top_waiter |
|
* - <0 - error |
|
*/ |
|
static int |
|
futex_proxy_trylock_atomic(u32 __user *pifutex, struct futex_hash_bucket *hb1, |
|
struct futex_hash_bucket *hb2, union futex_key *key1, |
|
union futex_key *key2, struct futex_pi_state **ps, |
|
struct task_struct **exiting, int set_waiters) |
|
{ |
|
struct futex_q *top_waiter = NULL; |
|
u32 curval; |
|
int ret; |
|
|
|
if (get_futex_value_locked(&curval, pifutex)) |
|
return -EFAULT; |
|
|
|
if (unlikely(should_fail_futex(true))) |
|
return -EFAULT; |
|
|
|
/* |
|
* Find the top_waiter and determine if there are additional waiters. |
|
* If the caller intends to requeue more than 1 waiter to pifutex, |
|
* force futex_lock_pi_atomic() to set the FUTEX_WAITERS bit now, |
|
* as we have means to handle the possible fault. If not, don't set |
|
* the bit unnecessarily as it will force the subsequent unlock to enter |
|
* the kernel. |
|
*/ |
|
top_waiter = futex_top_waiter(hb1, key1); |
|
|
|
/* There are no waiters, nothing for us to do. */ |
|
if (!top_waiter) |
|
return 0; |
|
|
|
/* |
|
* Ensure that this is a waiter sitting in futex_wait_requeue_pi() |
|
* and waiting on the 'waitqueue' futex which is always !PI. |
|
*/ |
|
if (!top_waiter->rt_waiter || top_waiter->pi_state) |
|
return -EINVAL; |
|
|
|
/* Ensure we requeue to the expected futex. */ |
|
if (!match_futex(top_waiter->requeue_pi_key, key2)) |
|
return -EINVAL; |
|
|
|
/* Ensure that this does not race against an early wakeup */ |
|
if (!futex_requeue_pi_prepare(top_waiter, NULL)) |
|
return -EAGAIN; |
|
|
|
/* |
|
* Try to take the lock for top_waiter and set the FUTEX_WAITERS bit |
|
* in the contended case or if @set_waiters is true. |
|
* |
|
* In the contended case PI state is attached to the lock owner. If |
|
* the user space lock can be acquired then PI state is attached to |
|
* the new owner (@top_waiter->task) when @set_waiters is true. |
|
*/ |
|
ret = futex_lock_pi_atomic(pifutex, hb2, key2, ps, top_waiter->task, |
|
exiting, set_waiters); |
|
if (ret == 1) { |
|
/* |
|
* Lock was acquired in user space and PI state was |
|
* attached to @top_waiter->task. That means state is fully |
|
* consistent and the waiter can return to user space |
|
* immediately after the wakeup. |
|
*/ |
|
requeue_pi_wake_futex(top_waiter, key2, hb2); |
|
} else if (ret < 0) { |
|
/* Rewind top_waiter::requeue_state */ |
|
futex_requeue_pi_complete(top_waiter, ret); |
|
} else { |
|
/* |
|
* futex_lock_pi_atomic() did not acquire the user space |
|
* futex, but managed to establish the proxy lock and pi |
|
* state. top_waiter::requeue_state cannot be fixed up here |
|
* because the waiter is not enqueued on the rtmutex |
|
* yet. This is handled at the callsite depending on the |
|
* result of rt_mutex_start_proxy_lock() which is |
|
* guaranteed to be reached with this function returning 0. |
|
*/ |
|
} |
|
return ret; |
|
} |
|
|
|
/** |
|
* futex_requeue() - Requeue waiters from uaddr1 to uaddr2 |
|
* @uaddr1: source futex user address |
|
* @flags: futex flags (FLAGS_SHARED, etc.) |
|
* @uaddr2: target futex user address |
|
* @nr_wake: number of waiters to wake (must be 1 for requeue_pi) |
|
* @nr_requeue: number of waiters to requeue (0-INT_MAX) |
|
* @cmpval: @uaddr1 expected value (or %NULL) |
|
* @requeue_pi: if we are attempting to requeue from a non-pi futex to a |
|
* pi futex (pi to pi requeue is not supported) |
|
* |
|
* Requeue waiters on uaddr1 to uaddr2. In the requeue_pi case, try to acquire |
|
* uaddr2 atomically on behalf of the top waiter. |
|
* |
|
* Return: |
|
* - >=0 - on success, the number of tasks requeued or woken; |
|
* - <0 - on error |
|
*/ |
|
static int futex_requeue(u32 __user *uaddr1, unsigned int flags, |
|
u32 __user *uaddr2, int nr_wake, int nr_requeue, |
|
u32 *cmpval, int requeue_pi) |
|
{ |
|
union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT; |
|
int task_count = 0, ret; |
|
struct futex_pi_state *pi_state = NULL; |
|
struct futex_hash_bucket *hb1, *hb2; |
|
struct futex_q *this, *next; |
|
DEFINE_WAKE_Q(wake_q); |
|
|
|
if (nr_wake < 0 || nr_requeue < 0) |
|
return -EINVAL; |
|
|
|
/* |
|
* When PI not supported: return -ENOSYS if requeue_pi is true, |
|
* consequently the compiler knows requeue_pi is always false past |
|
* this point which will optimize away all the conditional code |
|
* further down. |
|
*/ |
|
if (!IS_ENABLED(CONFIG_FUTEX_PI) && requeue_pi) |
|
return -ENOSYS; |
|
|
|
if (requeue_pi) { |
|
/* |
|
* Requeue PI only works on two distinct uaddrs. This |
|
* check is only valid for private futexes. See below. |
|
*/ |
|
if (uaddr1 == uaddr2) |
|
return -EINVAL; |
|
|
|
/* |
|
* futex_requeue() allows the caller to define the number |
|
* of waiters to wake up via the @nr_wake argument. With |
|
* REQUEUE_PI, waking up more than one waiter is creating |
|
* more problems than it solves. Waking up a waiter makes |
|
* only sense if the PI futex @uaddr2 is uncontended as |
|
* this allows the requeue code to acquire the futex |
|
* @uaddr2 before waking the waiter. The waiter can then |
|
* return to user space without further action. A secondary |
|
* wakeup would just make the futex_wait_requeue_pi() |
|
* handling more complex, because that code would have to |
|
* look up pi_state and do more or less all the handling |
|
* which the requeue code has to do for the to be requeued |
|
* waiters. So restrict the number of waiters to wake to |
|
* one, and only wake it up when the PI futex is |
|
* uncontended. Otherwise requeue it and let the unlock of |
|
* the PI futex handle the wakeup. |
|
* |
|
* All REQUEUE_PI users, e.g. pthread_cond_signal() and |
|
* pthread_cond_broadcast() must use nr_wake=1. |
|
*/ |
|
if (nr_wake != 1) |
|
return -EINVAL; |
|
|
|
/* |
|
* requeue_pi requires a pi_state, try to allocate it now |
|
* without any locks in case it fails. |
|
*/ |
|
if (refill_pi_state_cache()) |
|
return -ENOMEM; |
|
} |
|
|
|
retry: |
|
ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, FUTEX_READ); |
|
if (unlikely(ret != 0)) |
|
return ret; |
|
ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, |
|
requeue_pi ? FUTEX_WRITE : FUTEX_READ); |
|
if (unlikely(ret != 0)) |
|
return ret; |
|
|
|
/* |
|
* The check above which compares uaddrs is not sufficient for |
|
* shared futexes. We need to compare the keys: |
|
*/ |
|
if (requeue_pi && match_futex(&key1, &key2)) |
|
return -EINVAL; |
|
|
|
hb1 = hash_futex(&key1); |
|
hb2 = hash_futex(&key2); |
|
|
|
retry_private: |
|
hb_waiters_inc(hb2); |
|
double_lock_hb(hb1, hb2); |
|
|
|
if (likely(cmpval != NULL)) { |
|
u32 curval; |
|
|
|
ret = get_futex_value_locked(&curval, uaddr1); |
|
|
|
if (unlikely(ret)) { |
|
double_unlock_hb(hb1, hb2); |
|
hb_waiters_dec(hb2); |
|
|
|
ret = get_user(curval, uaddr1); |
|
if (ret) |
|
return ret; |
|
|
|
if (!(flags & FLAGS_SHARED)) |
|
goto retry_private; |
|
|
|
goto retry; |
|
} |
|
if (curval != *cmpval) { |
|
ret = -EAGAIN; |
|
goto out_unlock; |
|
} |
|
} |
|
|
|
if (requeue_pi) { |
|
struct task_struct *exiting = NULL; |
|
|
|
/* |
|
* Attempt to acquire uaddr2 and wake the top waiter. If we |
|
* intend to requeue waiters, force setting the FUTEX_WAITERS |
|
* bit. We force this here where we are able to easily handle |
|
* faults rather in the requeue loop below. |
|
* |
|
* Updates topwaiter::requeue_state if a top waiter exists. |
|
*/ |
|
ret = futex_proxy_trylock_atomic(uaddr2, hb1, hb2, &key1, |
|
&key2, &pi_state, |
|
&exiting, nr_requeue); |
|
|
|
/* |
|
* At this point the top_waiter has either taken uaddr2 or |
|
* is waiting on it. In both cases pi_state has been |
|
* established and an initial refcount on it. In case of an |
|
* error there's nothing. |
|
* |
|
* The top waiter's requeue_state is up to date: |
|
* |
|
* - If the lock was acquired atomically (ret == 1), then |
|
* the state is Q_REQUEUE_PI_LOCKED. |
|
* |
|
* The top waiter has been dequeued and woken up and can |
|
* return to user space immediately. The kernel/user |
|
* space state is consistent. In case that there must be |
|
* more waiters requeued the WAITERS bit in the user |
|
* space futex is set so the top waiter task has to go |
|
* into the syscall slowpath to unlock the futex. This |
|
* will block until this requeue operation has been |
|
* completed and the hash bucket locks have been |
|
* dropped. |
|
* |
|
* - If the trylock failed with an error (ret < 0) then |
|
* the state is either Q_REQUEUE_PI_NONE, i.e. "nothing |
|
* happened", or Q_REQUEUE_PI_IGNORE when there was an |
|
* interleaved early wakeup. |
|
* |
|
* - If the trylock did not succeed (ret == 0) then the |
|
* state is either Q_REQUEUE_PI_IN_PROGRESS or |
|
* Q_REQUEUE_PI_WAIT if an early wakeup interleaved. |
|
* This will be cleaned up in the loop below, which |
|
* cannot fail because futex_proxy_trylock_atomic() did |
|
* the same sanity checks for requeue_pi as the loop |
|
* below does. |
|
*/ |
|
switch (ret) { |
|
case 0: |
|
/* We hold a reference on the pi state. */ |
|
break; |
|
|
|
case 1: |
|
/* |
|
* futex_proxy_trylock_atomic() acquired the user space |
|
* futex. Adjust task_count. |
|
*/ |
|
task_count++; |
|
ret = 0; |
|
break; |
|
|
|
/* |
|
* If the above failed, then pi_state is NULL and |
|
* waiter::requeue_state is correct. |
|
*/ |
|
case -EFAULT: |
|
double_unlock_hb(hb1, hb2); |
|
hb_waiters_dec(hb2); |
|
ret = fault_in_user_writeable(uaddr2); |
|
if (!ret) |
|
goto retry; |
|
return ret; |
|
case -EBUSY: |
|
case -EAGAIN: |
|
/* |
|
* Two reasons for this: |
|
* - EBUSY: Owner is exiting and we just wait for the |
|
* exit to complete. |
|
* - EAGAIN: The user space value changed. |
|
*/ |
|
double_unlock_hb(hb1, hb2); |
|
hb_waiters_dec(hb2); |
|
/* |
|
* Handle the case where the owner is in the middle of |
|
* exiting. Wait for the exit to complete otherwise |
|
* this task might loop forever, aka. live lock. |
|
*/ |
|
wait_for_owner_exiting(ret, exiting); |
|
cond_resched(); |
|
goto retry; |
|
default: |
|
goto out_unlock; |
|
} |
|
} |
|
|
|
plist_for_each_entry_safe(this, next, &hb1->chain, list) { |
|
if (task_count - nr_wake >= nr_requeue) |
|
break; |
|
|
|
if (!match_futex(&this->key, &key1)) |
|
continue; |
|
|
|
/* |
|
* FUTEX_WAIT_REQUEUE_PI and FUTEX_CMP_REQUEUE_PI should always |
|
* be paired with each other and no other futex ops. |
|
* |
|
* We should never be requeueing a futex_q with a pi_state, |
|
* which is awaiting a futex_unlock_pi(). |
|
*/ |
|
if ((requeue_pi && !this->rt_waiter) || |
|
(!requeue_pi && this->rt_waiter) || |
|
this->pi_state) { |
|
ret = -EINVAL; |
|
break; |
|
} |
|
|
|
/* Plain futexes just wake or requeue and are done */ |
|
if (!requeue_pi) { |
|
if (++task_count <= nr_wake) |
|
mark_wake_futex(&wake_q, this); |
|
else |
|
requeue_futex(this, hb1, hb2, &key2); |
|
continue; |
|
} |
|
|
|
/* Ensure we requeue to the expected futex for requeue_pi. */ |
|
if (!match_futex(this->requeue_pi_key, &key2)) { |
|
ret = -EINVAL; |
|
break; |
|
} |
|
|
|
/* |
|
* Requeue nr_requeue waiters and possibly one more in the case |
|
* of requeue_pi if we couldn't acquire the lock atomically. |
|
* |
|
* Prepare the waiter to take the rt_mutex. Take a refcount |
|
* on the pi_state and store the pointer in the futex_q |
|
* object of the waiter. |
|
*/ |
|
get_pi_state(pi_state); |
|
|
|
/* Don't requeue when the waiter is already on the way out. */ |
|
if (!futex_requeue_pi_prepare(this, pi_state)) { |
|
/* |
|
* Early woken waiter signaled that it is on the |
|
* way out. Drop the pi_state reference and try the |
|
* next waiter. @this->pi_state is still NULL. |
|
*/ |
|
put_pi_state(pi_state); |
|
continue; |
|
} |
|
|
|
ret = rt_mutex_start_proxy_lock(&pi_state->pi_mutex, |
|
this->rt_waiter, |
|
this->task); |
|
|
|
if (ret == 1) { |
|
/* |
|
* We got the lock. We do neither drop the refcount |
|
* on pi_state nor clear this->pi_state because the |
|
* waiter needs the pi_state for cleaning up the |
|
* user space value. It will drop the refcount |
|
* after doing so. this::requeue_state is updated |
|
* in the wakeup as well. |
|
*/ |
|
requeue_pi_wake_futex(this, &key2, hb2); |
|
task_count++; |
|
} else if (!ret) { |
|
/* Waiter is queued, move it to hb2 */ |
|
requeue_futex(this, hb1, hb2, &key2); |
|
futex_requeue_pi_complete(this, 0); |
|
task_count++; |
|
} else { |
|
/* |
|
* rt_mutex_start_proxy_lock() detected a potential |
|
* deadlock when we tried to queue that waiter. |
|
* Drop the pi_state reference which we took above |
|
* and remove the pointer to the state from the |
|
* waiters futex_q object. |
|
*/ |
|
this->pi_state = NULL; |
|
put_pi_state(pi_state); |
|
futex_requeue_pi_complete(this, ret); |
|
/* |
|
* We stop queueing more waiters and let user space |
|
* deal with the mess. |
|
*/ |
|
break; |
|
} |
|
} |
|
|
|
/* |
|
* We took an extra initial reference to the pi_state in |
|
* futex_proxy_trylock_atomic(). We need to drop it here again. |
|
*/ |
|
put_pi_state(pi_state); |
|
|
|
out_unlock: |
|
double_unlock_hb(hb1, hb2); |
|
wake_up_q(&wake_q); |
|
hb_waiters_dec(hb2); |
|
return ret ? ret : task_count; |
|
} |
|
|
|
/* The key must be already stored in q->key. */ |
|
static inline struct futex_hash_bucket *queue_lock(struct futex_q *q) |
|
__acquires(&hb->lock) |
|
{ |
|
struct futex_hash_bucket *hb; |
|
|
|
hb = hash_futex(&q->key); |
|
|
|
/* |
|
* Increment the counter before taking the lock so that |
|
* a potential waker won't miss a to-be-slept task that is |
|
* waiting for the spinlock. This is safe as all queue_lock() |
|
* users end up calling queue_me(). Similarly, for housekeeping, |
|
* decrement the counter at queue_unlock() when some error has |
|
* occurred and we don't end up adding the task to the list. |
|
*/ |
|
hb_waiters_inc(hb); /* implies smp_mb(); (A) */ |
|
|
|
q->lock_ptr = &hb->lock; |
|
|
|
spin_lock(&hb->lock); |
|
return hb; |
|
} |
|
|
|
static inline void |
|
queue_unlock(struct futex_hash_bucket *hb) |
|
__releases(&hb->lock) |
|
{ |
|
spin_unlock(&hb->lock); |
|
hb_waiters_dec(hb); |
|
} |
|
|
|
static inline void __queue_me(struct futex_q *q, struct futex_hash_bucket *hb) |
|
{ |
|
int prio; |
|
|
|
/* |
|
* The priority used to register this element is |
|
* - either the real thread-priority for the real-time threads |
|
* (i.e. threads with a priority lower than MAX_RT_PRIO) |
|
* - or MAX_RT_PRIO for non-RT threads. |
|
* Thus, all RT-threads are woken first in priority order, and |
|
* the others are woken last, in FIFO order. |
|
*/ |
|
prio = min(current->normal_prio, MAX_RT_PRIO); |
|
|
|
plist_node_init(&q->list, prio); |
|
plist_add(&q->list, &hb->chain); |
|
q->task = current; |
|
} |
|
|
|
/** |
|
* queue_me() - Enqueue the futex_q on the futex_hash_bucket |
|
* @q: The futex_q to enqueue |
|
* @hb: The destination hash bucket |
|
* |
|
* The hb->lock must be held by the caller, and is released here. A call to |
|
* queue_me() is typically paired with exactly one call to unqueue_me(). The |
|
* exceptions involve the PI related operations, which may use unqueue_me_pi() |
|
* or nothing if the unqueue is done as part of the wake process and the unqueue |
|
* state is implicit in the state of woken task (see futex_wait_requeue_pi() for |
|
* an example). |
|
*/ |
|
static inline void queue_me(struct futex_q *q, struct futex_hash_bucket *hb) |
|
__releases(&hb->lock) |
|
{ |
|
__queue_me(q, hb); |
|
spin_unlock(&hb->lock); |
|
} |
|
|
|
/** |
|
* unqueue_me() - Remove the futex_q from its futex_hash_bucket |
|
* @q: The futex_q to unqueue |
|
* |
|
* The q->lock_ptr must not be held by the caller. A call to unqueue_me() must |
|
* be paired with exactly one earlier call to queue_me(). |
|
* |
|
* Return: |
|
* - 1 - if the futex_q was still queued (and we removed unqueued it); |
|
* - 0 - if the futex_q was already removed by the waking thread |
|
*/ |
|
static int unqueue_me(struct futex_q *q) |
|
{ |
|
spinlock_t *lock_ptr; |
|
int ret = 0; |
|
|
|
/* In the common case we don't take the spinlock, which is nice. */ |
|
retry: |
|
/* |
|
* q->lock_ptr can change between this read and the following spin_lock. |
|
* Use READ_ONCE to forbid the compiler from reloading q->lock_ptr and |
|
* optimizing lock_ptr out of the logic below. |
|
*/ |
|
lock_ptr = READ_ONCE(q->lock_ptr); |
|
if (lock_ptr != NULL) { |
|
spin_lock(lock_ptr); |
|
/* |
|
* q->lock_ptr can change between reading it and |
|
* spin_lock(), causing us to take the wrong lock. This |
|
* corrects the race condition. |
|
* |
|
* Reasoning goes like this: if we have the wrong lock, |
|
* q->lock_ptr must have changed (maybe several times) |
|
* between reading it and the spin_lock(). It can |
|
* change again after the spin_lock() but only if it was |
|
* already changed before the spin_lock(). It cannot, |
|
* however, change back to the original value. Therefore |
|
* we can detect whether we acquired the correct lock. |
|
*/ |
|
if (unlikely(lock_ptr != q->lock_ptr)) { |
|
spin_unlock(lock_ptr); |
|
goto retry; |
|
} |
|
__unqueue_futex(q); |
|
|
|
BUG_ON(q->pi_state); |
|
|
|
spin_unlock(lock_ptr); |
|
ret = 1; |
|
} |
|
|
|
return ret; |
|
} |
|
|
|
/* |
|
* PI futexes can not be requeued and must remove themselves from the |
|
* hash bucket. The hash bucket lock (i.e. lock_ptr) is held. |
|
*/ |
|
static void unqueue_me_pi(struct futex_q *q) |
|
{ |
|
__unqueue_futex(q); |
|
|
|
BUG_ON(!q->pi_state); |
|
put_pi_state(q->pi_state); |
|
q->pi_state = NULL; |
|
} |
|
|
|
static int __fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q, |
|
struct task_struct *argowner) |
|
{ |
|
struct futex_pi_state *pi_state = q->pi_state; |
|
struct task_struct *oldowner, *newowner; |
|
u32 uval, curval, newval, newtid; |
|
int err = 0; |
|
|
|
oldowner = pi_state->owner; |
|
|
|
/* |
|
* We are here because either: |
|
* |
|
* - we stole the lock and pi_state->owner needs updating to reflect |
|
* that (@argowner == current), |
|
* |
|
* or: |
|
* |
|
* - someone stole our lock and we need to fix things to point to the |
|
* new owner (@argowner == NULL). |
|
* |
|
* Either way, we have to replace the TID in the user space variable. |
|
* This must be atomic as we have to preserve the owner died bit here. |
|
* |
|
* Note: We write the user space value _before_ changing the pi_state |
|
* because we can fault here. Imagine swapped out pages or a fork |
|
* that marked all the anonymous memory readonly for cow. |
|
* |
|
* Modifying pi_state _before_ the user space value would leave the |
|
* pi_state in an inconsistent state when we fault here, because we |
|
* need to drop the locks to handle the fault. This might be observed |
|
* in the PID checks when attaching to PI state . |
|
*/ |
|
retry: |
|
if (!argowner) { |
|
if (oldowner != current) { |
|
/* |
|
* We raced against a concurrent self; things are |
|
* already fixed up. Nothing to do. |
|
*/ |
|
return 0; |
|
} |
|
|
|
if (__rt_mutex_futex_trylock(&pi_state->pi_mutex)) { |
|
/* We got the lock. pi_state is correct. Tell caller. */ |
|
return 1; |
|
} |
|
|
|
/* |
|
* The trylock just failed, so either there is an owner or |
|
* there is a higher priority waiter than this one. |
|
*/ |
|
newowner = rt_mutex_owner(&pi_state->pi_mutex); |
|
/* |
|
* If the higher priority waiter has not yet taken over the |
|
* rtmutex then newowner is NULL. We can't return here with |
|
* that state because it's inconsistent vs. the user space |
|
* state. So drop the locks and try again. It's a valid |
|
* situation and not any different from the other retry |
|
* conditions. |
|
*/ |
|
if (unlikely(!newowner)) { |
|
err = -EAGAIN; |
|
goto handle_err; |
|
} |
|
} else { |
|
WARN_ON_ONCE(argowner != current); |
|
if (oldowner == current) { |
|
/* |
|
* We raced against a concurrent self; things are |
|
* already fixed up. Nothing to do. |
|
*/ |
|
return 1; |
|
} |
|
newowner = argowner; |
|
} |
|
|
|
newtid = task_pid_vnr(newowner) | FUTEX_WAITERS; |
|
/* Owner died? */ |
|
if (!pi_state->owner) |
|
newtid |= FUTEX_OWNER_DIED; |
|
|
|
err = get_futex_value_locked(&uval, uaddr); |
|
if (err) |
|
goto handle_err; |
|
|
|
for (;;) { |
|
newval = (uval & FUTEX_OWNER_DIED) | newtid; |
|
|
|
err = cmpxchg_futex_value_locked(&curval, uaddr, uval, newval); |
|
if (err) |
|
goto handle_err; |
|
|
|
if (curval == uval) |
|
break; |
|
uval = curval; |
|
} |
|
|
|
/* |
|
* We fixed up user space. Now we need to fix the pi_state |
|
* itself. |
|
*/ |
|
pi_state_update_owner(pi_state, newowner); |
|
|
|
return argowner == current; |
|
|
|
/* |
|
* In order to reschedule or handle a page fault, we need to drop the |
|
* locks here. In the case of a fault, this gives the other task |
|
* (either the highest priority waiter itself or the task which stole |
|
* the rtmutex) the chance to try the fixup of the pi_state. So once we |
|
* are back from handling the fault we need to check the pi_state after |
|
* reacquiring the locks and before trying to do another fixup. When |
|
* the fixup has been done already we simply return. |
|
* |
|
* Note: we hold both hb->lock and pi_mutex->wait_lock. We can safely |
|
* drop hb->lock since the caller owns the hb -> futex_q relation. |
|
* Dropping the pi_mutex->wait_lock requires the state revalidate. |
|
*/ |
|
handle_err: |
|
raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock); |
|
spin_unlock(q->lock_ptr); |
|
|
|
switch (err) { |
|
case -EFAULT: |
|
err = fault_in_user_writeable(uaddr); |
|
break; |
|
|
|
case -EAGAIN: |
|
cond_resched(); |
|
err = 0; |
|
break; |
|
|
|
default: |
|
WARN_ON_ONCE(1); |
|
break; |
|
} |
|
|
|
spin_lock(q->lock_ptr); |
|
raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock); |
|
|
|
/* |
|
* Check if someone else fixed it for us: |
|
*/ |
|
if (pi_state->owner != oldowner) |
|
return argowner == current; |
|
|
|
/* Retry if err was -EAGAIN or the fault in succeeded */ |
|
if (!err) |
|
goto retry; |
|
|
|
/* |
|
* fault_in_user_writeable() failed so user state is immutable. At |
|
* best we can make the kernel state consistent but user state will |
|
* be most likely hosed and any subsequent unlock operation will be |
|
* rejected due to PI futex rule [10]. |
|
* |
|
* Ensure that the rtmutex owner is also the pi_state owner despite |
|
* the user space value claiming something different. There is no |
|
* point in unlocking the rtmutex if current is the owner as it |
|
* would need to wait until the next waiter has taken the rtmutex |
|
* to guarantee consistent state. Keep it simple. Userspace asked |
|
* for this wreckaged state. |
|
* |
|
* The rtmutex has an owner - either current or some other |
|
* task. See the EAGAIN loop above. |
|
*/ |
|
pi_state_update_owner(pi_state, rt_mutex_owner(&pi_state->pi_mutex)); |
|
|
|
return err; |
|
} |
|
|
|
static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q, |
|
struct task_struct *argowner) |
|
{ |
|
struct futex_pi_state *pi_state = q->pi_state; |
|
int ret; |
|
|
|
lockdep_assert_held(q->lock_ptr); |
|
|
|
raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock); |
|
ret = __fixup_pi_state_owner(uaddr, q, argowner); |
|
raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock); |
|
return ret; |
|
} |
|
|
|
static long futex_wait_restart(struct restart_block *restart); |
|
|
|
/** |
|
* fixup_owner() - Post lock pi_state and corner case management |
|
* @uaddr: user address of the futex |
|
* @q: futex_q (contains pi_state and access to the rt_mutex) |
|
* @locked: if the attempt to take the rt_mutex succeeded (1) or not (0) |
|
* |
|
* After attempting to lock an rt_mutex, this function is called to cleanup |
|
* the pi_state owner as well as handle race conditions that may allow us to |
|
* acquire the lock. Must be called with the hb lock held. |
|
* |
|
* Return: |
|
* - 1 - success, lock taken; |
|
* - 0 - success, lock not taken; |
|
* - <0 - on error (-EFAULT) |
|
*/ |
|
static int fixup_owner(u32 __user *uaddr, struct futex_q *q, int locked) |
|
{ |
|
if (locked) { |
|
/* |
|
* Got the lock. We might not be the anticipated owner if we |
|
* did a lock-steal - fix up the PI-state in that case: |
|
* |
|
* Speculative pi_state->owner read (we don't hold wait_lock); |
|
* since we own the lock pi_state->owner == current is the |
|
* stable state, anything else needs more attention. |
|
*/ |
|
if (q->pi_state->owner != current) |
|
return fixup_pi_state_owner(uaddr, q, current); |
|
return 1; |
|
} |
|
|
|
/* |
|
* If we didn't get the lock; check if anybody stole it from us. In |
|
* that case, we need to fix up the uval to point to them instead of |
|
* us, otherwise bad things happen. [10] |
|
* |
|
* Another speculative read; pi_state->owner == current is unstable |
|
* but needs our attention. |
|
*/ |
|
if (q->pi_state->owner == current) |
|
return fixup_pi_state_owner(uaddr, q, NULL); |
|
|
|
/* |
|
* Paranoia check. If we did not take the lock, then we should not be |
|
* the owner of the rt_mutex. Warn and establish consistent state. |
|
*/ |
|
if (WARN_ON_ONCE(rt_mutex_owner(&q->pi_state->pi_mutex) == current)) |
|
return fixup_pi_state_owner(uaddr, q, current); |
|
|
|
return 0; |
|
} |
|
|
|
/** |
|
* futex_wait_queue_me() - queue_me() and wait for wakeup, timeout, or signal |
|
* @hb: the futex hash bucket, must be locked by the caller |
|
* @q: the futex_q to queue up on |
|
* @timeout: the prepared hrtimer_sleeper, or null for no timeout |
|
*/ |
|
static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q, |
|
struct hrtimer_sleeper *timeout) |
|
{ |
|
/* |
|
* The task state is guaranteed to be set before another task can |
|
* wake it. set_current_state() is implemented using smp_store_mb() and |
|
* queue_me() calls spin_unlock() upon completion, both serializing |
|
* access to the hash list and forcing another memory barrier. |
|
*/ |
|
set_current_state(TASK_INTERRUPTIBLE); |
|
queue_me(q, hb); |
|
|
|
/* Arm the timer */ |
|
if (timeout) |
|
hrtimer_sleeper_start_expires(timeout, HRTIMER_MODE_ABS); |
|
|
|
/* |
|
* If we have been removed from the hash list, then another task |
|
* has tried to wake us, and we can skip the call to schedule(). |
|
*/ |
|
if (likely(!plist_node_empty(&q->list))) { |
|
/* |
|
* If the timer has already expired, current will already be |
|
* flagged for rescheduling. Only call schedule if there |
|
* is no timeout, or if it has yet to expire. |
|
*/ |
|
if (!timeout || timeout->task) |
|
freezable_schedule(); |
|
} |
|
__set_current_state(TASK_RUNNING); |
|
} |
|
|
|
/** |
|
* futex_wait_setup() - Prepare to wait on a futex |
|
* @uaddr: the futex userspace address |
|
* @val: the expected value |
|
* @flags: futex flags (FLAGS_SHARED, etc.) |
|
* @q: the associated futex_q |
|
* @hb: storage for hash_bucket pointer to be returned to caller |
|
* |
|
* Setup the futex_q and locate the hash_bucket. Get the futex value and |
|
* compare it with the expected value. Handle atomic faults internally. |
|
* Return with the hb lock held on success, and unlocked on failure. |
|
* |
|
* Return: |
|
* - 0 - uaddr contains val and hb has been locked; |
|
* - <1 - -EFAULT or -EWOULDBLOCK (uaddr does not contain val) and hb is unlocked |
|
*/ |
|
static int futex_wait_setup(u32 __user *uaddr, u32 val, unsigned int flags, |
|
struct futex_q *q, struct futex_hash_bucket **hb) |
|
{ |
|
u32 uval; |
|
int ret; |
|
|
|
/* |
|
* Access the page AFTER the hash-bucket is locked. |
|
* Order is important: |
|
* |
|
* Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val); |
|
* Userspace waker: if (cond(var)) { var = new; futex_wake(&var); } |
|
* |
|
* The basic logical guarantee of a futex is that it blocks ONLY |
|
* if cond(var) is known to be true at the time of blocking, for |
|
* any cond. If we locked the hash-bucket after testing *uaddr, that |
|
* would open a race condition where we could block indefinitely with |
|
* cond(var) false, which would violate the guarantee. |
|
* |
|
* On the other hand, we insert q and release the hash-bucket only |
|
* after testing *uaddr. This guarantees that futex_wait() will NOT |
|
* absorb a wakeup if *uaddr does not match the desired values |
|
* while the syscall executes. |
|
*/ |
|
retry: |
|
ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q->key, FUTEX_READ); |
|
if (unlikely(ret != 0)) |
|
return ret; |
|
|
|
retry_private: |
|
*hb = queue_lock(q); |
|
|
|
ret = get_futex_value_locked(&uval, uaddr); |
|
|
|
if (ret) { |
|
queue_unlock(*hb); |
|
|
|
ret = get_user(uval, uaddr); |
|
if (ret) |
|
return ret; |
|
|
|
if (!(flags & FLAGS_SHARED)) |
|
goto retry_private; |
|
|
|
goto retry; |
|
} |
|
|
|
if (uval != val) { |
|
queue_unlock(*hb); |
|
ret = -EWOULDBLOCK; |
|
} |
|
|
|
return ret; |
|
} |
|
|
|
static int futex_wait(u32 __user *uaddr, unsigned int flags, u32 val, |
|
ktime_t *abs_time, u32 bitset) |
|
{ |
|
struct hrtimer_sleeper timeout, *to; |
|
struct restart_block *restart; |
|
struct futex_hash_bucket *hb; |
|
struct futex_q q = futex_q_init; |
|
int ret; |
|
|
|
if (!bitset) |
|
return -EINVAL; |
|
q.bitset = bitset; |
|
|
|
to = futex_setup_timer(abs_time, &timeout, flags, |
|
current->timer_slack_ns); |
|
retry: |
|
/* |
|
* Prepare to wait on uaddr. On success, it holds hb->lock and q |
|
* is initialized. |
|
*/ |
|
ret = futex_wait_setup(uaddr, val, flags, &q, &hb); |
|
if (ret) |
|
goto out; |
|
|
|
/* queue_me and wait for wakeup, timeout, or a signal. */ |
|
futex_wait_queue_me(hb, &q, to); |
|
|
|
/* If we were woken (and unqueued), we succeeded, whatever. */ |
|
ret = 0; |
|
if (!unqueue_me(&q)) |
|
goto out; |
|
ret = -ETIMEDOUT; |
|
if (to && !to->task) |
|
goto out; |
|
|
|
/* |
|
* We expect signal_pending(current), but we might be the |
|
* victim of a spurious wakeup as well. |
|
*/ |
|
if (!signal_pending(current)) |
|
goto retry; |
|
|
|
ret = -ERESTARTSYS; |
|
if (!abs_time) |
|
goto out; |
|
|
|
restart = ¤t->restart_block; |
|
restart->futex.uaddr = uaddr; |
|
restart->futex.val = val; |
|
restart->futex.time = *abs_time; |
|
restart->futex.bitset = bitset; |
|
restart->futex.flags = flags | FLAGS_HAS_TIMEOUT; |
|
|
|
ret = set_restart_fn(restart, futex_wait_restart); |
|
|
|
out: |
|
if (to) { |
|
hrtimer_cancel(&to->timer); |
|
destroy_hrtimer_on_stack(&to->timer); |
|
} |
|
return ret; |
|
} |
|
|
|
|
|
static long futex_wait_restart(struct restart_block *restart) |
|
{ |
|
u32 __user *uaddr = restart->futex.uaddr; |
|
ktime_t t, *tp = NULL; |
|
|
|
if (restart->futex.flags & FLAGS_HAS_TIMEOUT) { |
|
t = restart->futex.time; |
|
tp = &t; |
|
} |
|
restart->fn = do_no_restart_syscall; |
|
|
|
return (long)futex_wait(uaddr, restart->futex.flags, |
|
restart->futex.val, tp, restart->futex.bitset); |
|
} |
|
|
|
|
|
/* |
|
* Userspace tried a 0 -> TID atomic transition of the futex value |
|
* and failed. The kernel side here does the whole locking operation: |
|
* if there are waiters then it will block as a consequence of relying |
|
* on rt-mutexes, it does PI, etc. (Due to races the kernel might see |
|
* a 0 value of the futex too.). |
|
* |
|
* Also serves as futex trylock_pi()'ing, and due semantics. |
|
*/ |
|
static int futex_lock_pi(u32 __user *uaddr, unsigned int flags, |
|
ktime_t *time, int trylock) |
|
{ |
|
struct hrtimer_sleeper timeout, *to; |
|
struct task_struct *exiting = NULL; |
|
struct rt_mutex_waiter rt_waiter; |
|
struct futex_hash_bucket *hb; |
|
struct futex_q q = futex_q_init; |
|
int res, ret; |
|
|
|
if (!IS_ENABLED(CONFIG_FUTEX_PI)) |
|
return -ENOSYS; |
|
|
|
if (refill_pi_state_cache()) |
|
return -ENOMEM; |
|
|
|
to = futex_setup_timer(time, &timeout, flags, 0); |
|
|
|
retry: |
|
ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q.key, FUTEX_WRITE); |
|
if (unlikely(ret != 0)) |
|
goto out; |
|
|
|
retry_private: |
|
hb = queue_lock(&q); |
|
|
|
ret = futex_lock_pi_atomic(uaddr, hb, &q.key, &q.pi_state, current, |
|
&exiting, 0); |
|
if (unlikely(ret)) { |
|
/* |
|
* Atomic work succeeded and we got the lock, |
|
* or failed. Either way, we do _not_ block. |
|
*/ |
|
switch (ret) { |
|
case 1: |
|
/* We got the lock. */ |
|
ret = 0; |
|
goto out_unlock_put_key; |
|
case -EFAULT: |
|
goto uaddr_faulted; |
|
case -EBUSY: |
|
case -EAGAIN: |
|
/* |
|
* Two reasons for this: |
|
* - EBUSY: Task is exiting and we just wait for the |
|
* exit to complete. |
|
* - EAGAIN: The user space value changed. |
|
*/ |
|
queue_unlock(hb); |
|
/* |
|
* Handle the case where the owner is in the middle of |
|
* exiting. Wait for the exit to complete otherwise |
|
* this task might loop forever, aka. live lock. |
|
*/ |
|
wait_for_owner_exiting(ret, exiting); |
|
cond_resched(); |
|
goto retry; |
|
default: |
|
goto out_unlock_put_key; |
|
} |
|
} |
|
|
|
WARN_ON(!q.pi_state); |
|
|
|
/* |
|
* Only actually queue now that the atomic ops are done: |
|
*/ |
|
__queue_me(&q, hb); |
|
|
|
if (trylock) { |
|
ret = rt_mutex_futex_trylock(&q.pi_state->pi_mutex); |
|
/* Fixup the trylock return value: */ |
|
ret = ret ? 0 : -EWOULDBLOCK; |
|
goto no_block; |
|
} |
|
|
|
rt_mutex_init_waiter(&rt_waiter); |
|
|
|
/* |
|
* On PREEMPT_RT_FULL, when hb->lock becomes an rt_mutex, we must not |
|
* hold it while doing rt_mutex_start_proxy(), because then it will |
|
* include hb->lock in the blocking chain, even through we'll not in |
|
* fact hold it while blocking. This will lead it to report -EDEADLK |
|
* and BUG when futex_unlock_pi() interleaves with this. |
|
* |
|
* Therefore acquire wait_lock while holding hb->lock, but drop the |
|
* latter before calling __rt_mutex_start_proxy_lock(). This |
|
* interleaves with futex_unlock_pi() -- which does a similar lock |
|
* handoff -- such that the latter can observe the futex_q::pi_state |
|
* before __rt_mutex_start_proxy_lock() is done. |
|
*/ |
|
raw_spin_lock_irq(&q.pi_state->pi_mutex.wait_lock); |
|
spin_unlock(q.lock_ptr); |
|
/* |
|
* __rt_mutex_start_proxy_lock() unconditionally enqueues the @rt_waiter |
|
* such that futex_unlock_pi() is guaranteed to observe the waiter when |
|
* it sees the futex_q::pi_state. |
|
*/ |
|
ret = __rt_mutex_start_proxy_lock(&q.pi_state->pi_mutex, &rt_waiter, current); |
|
raw_spin_unlock_irq(&q.pi_state->pi_mutex.wait_lock); |
|
|
|
if (ret) { |
|
if (ret == 1) |
|
ret = 0; |
|
goto cleanup; |
|
} |
|
|
|
if (unlikely(to)) |
|
hrtimer_sleeper_start_expires(to, HRTIMER_MODE_ABS); |
|
|
|
ret = rt_mutex_wait_proxy_lock(&q.pi_state->pi_mutex, to, &rt_waiter); |
|
|
|
cleanup: |
|
spin_lock(q.lock_ptr); |
|
/* |
|
* If we failed to acquire the lock (deadlock/signal/timeout), we must |
|
* first acquire the hb->lock before removing the lock from the |
|
* rt_mutex waitqueue, such that we can keep the hb and rt_mutex wait |
|
* lists consistent. |
|
* |
|
* In particular; it is important that futex_unlock_pi() can not |
|
* observe this inconsistency. |
|
*/ |
|
if (ret && !rt_mutex_cleanup_proxy_lock(&q.pi_state->pi_mutex, &rt_waiter)) |
|
ret = 0; |
|
|
|
no_block: |
|
/* |
|
* Fixup the pi_state owner and possibly acquire the lock if we |
|
* haven't already. |
|
*/ |
|
res = fixup_owner(uaddr, &q, !ret); |
|
/* |
|
* If fixup_owner() returned an error, propagate that. If it acquired |
|
* the lock, clear our -ETIMEDOUT or -EINTR. |
|
*/ |
|
if (res) |
|
ret = (res < 0) ? res : 0; |
|
|
|
unqueue_me_pi(&q); |
|
spin_unlock(q.lock_ptr); |
|
goto out; |
|
|
|
out_unlock_put_key: |
|
queue_unlock(hb); |
|
|
|
out: |
|
if (to) { |
|
hrtimer_cancel(&to->timer); |
|
destroy_hrtimer_on_stack(&to->timer); |
|
} |
|
return ret != -EINTR ? ret : -ERESTARTNOINTR; |
|
|
|
uaddr_faulted: |
|
queue_unlock(hb); |
|
|
|
ret = fault_in_user_writeable(uaddr); |
|
if (ret) |
|
goto out; |
|
|
|
if (!(flags & FLAGS_SHARED)) |
|
goto retry_private; |
|
|
|
goto retry; |
|
} |
|
|
|
/* |
|
* Userspace attempted a TID -> 0 atomic transition, and failed. |
|
* This is the in-kernel slowpath: we look up the PI state (if any), |
|
* and do the rt-mutex unlock. |
|
*/ |
|
static int futex_unlock_pi(u32 __user *uaddr, unsigned int flags) |
|
{ |
|
u32 curval, uval, vpid = task_pid_vnr(current); |
|
union futex_key key = FUTEX_KEY_INIT; |
|
struct futex_hash_bucket *hb; |
|
struct futex_q *top_waiter; |
|
int ret; |
|
|
|
if (!IS_ENABLED(CONFIG_FUTEX_PI)) |
|
return -ENOSYS; |
|
|
|
retry: |
|
if (get_user(uval, uaddr)) |
|
return -EFAULT; |
|
/* |
|
* We release only a lock we actually own: |
|
*/ |
|
if ((uval & FUTEX_TID_MASK) != vpid) |
|
return -EPERM; |
|
|
|
ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, FUTEX_WRITE); |
|
if (ret) |
|
return ret; |
|
|
|
hb = hash_futex(&key); |
|
spin_lock(&hb->lock); |
|
|
|
/* |
|
* Check waiters first. We do not trust user space values at |
|
* all and we at least want to know if user space fiddled |
|
* with the futex value instead of blindly unlocking. |
|
*/ |
|
top_waiter = futex_top_waiter(hb, &key); |
|
if (top_waiter) { |
|
struct futex_pi_state *pi_state = top_waiter->pi_state; |
|
|
|
ret = -EINVAL; |
|
if (!pi_state) |
|
goto out_unlock; |
|
|
|
/* |
|
* If current does not own the pi_state then the futex is |
|
* inconsistent and user space fiddled with the futex value. |
|
*/ |
|
if (pi_state->owner != current) |
|
goto out_unlock; |
|
|
|
get_pi_state(pi_state); |
|
/* |
|
* By taking wait_lock while still holding hb->lock, we ensure |
|
* there is no point where we hold neither; and therefore |
|
* wake_futex_pi() must observe a state consistent with what we |
|
* observed. |
|
* |
|
* In particular; this forces __rt_mutex_start_proxy() to |
|
* complete such that we're guaranteed to observe the |
|
* rt_waiter. Also see the WARN in wake_futex_pi(). |
|
*/ |
|
raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock); |
|
spin_unlock(&hb->lock); |
|
|
|
/* drops pi_state->pi_mutex.wait_lock */ |
|
ret = wake_futex_pi(uaddr, uval, pi_state); |
|
|
|
put_pi_state(pi_state); |
|
|
|
/* |
|
* Success, we're done! No tricky corner cases. |
|
*/ |
|
if (!ret) |
|
return ret; |
|
/* |
|
* The atomic access to the futex value generated a |
|
* pagefault, so retry the user-access and the wakeup: |
|
*/ |
|
if (ret == -EFAULT) |
|
goto pi_faulted; |
|
/* |
|
* A unconditional UNLOCK_PI op raced against a waiter |
|
* setting the FUTEX_WAITERS bit. Try again. |
|
*/ |
|
if (ret == -EAGAIN) |
|
goto pi_retry; |
|
/* |
|
* wake_futex_pi has detected invalid state. Tell user |
|
* space. |
|
*/ |
|
return ret; |
|
} |
|
|
|
/* |
|
* We have no kernel internal state, i.e. no waiters in the |
|
* kernel. Waiters which are about to queue themselves are stuck |
|
* on hb->lock. So we can safely ignore them. We do neither |
|
* preserve the WAITERS bit not the OWNER_DIED one. We are the |
|
* owner. |
|
*/ |
|
if ((ret = cmpxchg_futex_value_locked(&curval, uaddr, uval, 0))) { |
|
spin_unlock(&hb->lock); |
|
switch (ret) { |
|
case -EFAULT: |
|
goto pi_faulted; |
|
|
|
case -EAGAIN: |
|
goto pi_retry; |
|
|
|
default: |
|
WARN_ON_ONCE(1); |
|
return ret; |
|
} |
|
} |
|
|
|
/* |
|
* If uval has changed, let user space handle it. |
|
*/ |
|
ret = (curval == uval) ? 0 : -EAGAIN; |
|
|
|
out_unlock: |
|
spin_unlock(&hb->lock); |
|
return ret; |
|
|
|
pi_retry: |
|
cond_resched(); |
|
goto retry; |
|
|
|
pi_faulted: |
|
|
|
ret = fault_in_user_writeable(uaddr); |
|
if (!ret) |
|
goto retry; |
|
|
|
return ret; |
|
} |
|
|
|
/** |
|
* handle_early_requeue_pi_wakeup() - Handle early wakeup on the initial futex |
|
* @hb: the hash_bucket futex_q was original enqueued on |
|
* @q: the futex_q woken while waiting to be requeued |
|
* @timeout: the timeout associated with the wait (NULL if none) |
|
* |
|
* Determine the cause for the early wakeup. |
|
* |
|
* Return: |
|
* -EWOULDBLOCK or -ETIMEDOUT or -ERESTARTNOINTR |
|
*/ |
|
static inline |
|
int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb, |
|
struct futex_q *q, |
|
struct hrtimer_sleeper *timeout) |
|
{ |
|
int ret; |
|
|
|
/* |
|
* With the hb lock held, we avoid races while we process the wakeup. |
|
* We only need to hold hb (and not hb2) to ensure atomicity as the |
|
* wakeup code can't change q.key from uaddr to uaddr2 if we hold hb. |
|
* It can't be requeued from uaddr2 to something else since we don't |
|
* support a PI aware source futex for requeue. |
|
*/ |
|
WARN_ON_ONCE(&hb->lock != q->lock_ptr); |
|
|
|
/* |
|
* We were woken prior to requeue by a timeout or a signal. |
|
* Unqueue the futex_q and determine which it was. |
|
*/ |
|
plist_del(&q->list, &hb->chain); |
|
hb_waiters_dec(hb); |
|
|
|
/* Handle spurious wakeups gracefully */ |
|
ret = -EWOULDBLOCK; |
|
if (timeout && !timeout->task) |
|
ret = -ETIMEDOUT; |
|
else if (signal_pending(current)) |
|
ret = -ERESTARTNOINTR; |
|
return ret; |
|
} |
|
|
|
/** |
|
* futex_wait_requeue_pi() - Wait on uaddr and take uaddr2 |
|
* @uaddr: the futex we initially wait on (non-pi) |
|
* @flags: futex flags (FLAGS_SHARED, FLAGS_CLOCKRT, etc.), they must be |
|
* the same type, no requeueing from private to shared, etc. |
|
* @val: the expected value of uaddr |
|
* @abs_time: absolute timeout |
|
* @bitset: 32 bit wakeup bitset set by userspace, defaults to all |
|
* @uaddr2: the pi futex we will take prior to returning to user-space |
|
* |
|
* The caller will wait on uaddr and will be requeued by futex_requeue() to |
|
* uaddr2 which must be PI aware and unique from uaddr. Normal wakeup will wake |
|
* on uaddr2 and complete the acquisition of the rt_mutex prior to returning to |
|
* userspace. This ensures the rt_mutex maintains an owner when it has waiters; |
|
* without one, the pi logic would not know which task to boost/deboost, if |
|
* there was a need to. |
|
* |
|
* We call schedule in futex_wait_queue_me() when we enqueue and return there |
|
* via the following-- |
|
* 1) wakeup on uaddr2 after an atomic lock acquisition by futex_requeue() |
|
* 2) wakeup on uaddr2 after a requeue |
|
* 3) signal |
|
* 4) timeout |
|
* |
|
* If 3, cleanup and return -ERESTARTNOINTR. |
|
* |
|
* If 2, we may then block on trying to take the rt_mutex and return via: |
|
* 5) successful lock |
|
* 6) signal |
|
* 7) timeout |
|
* 8) other lock acquisition failure |
|
* |
|
* If 6, return -EWOULDBLOCK (restarting the syscall would do the same). |
|
* |
|
* If 4 or 7, we cleanup and return with -ETIMEDOUT. |
|
* |
|
* Return: |
|
* - 0 - On success; |
|
* - <0 - On error |
|
*/ |
|
static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags, |
|
u32 val, ktime_t *abs_time, u32 bitset, |
|
u32 __user *uaddr2) |
|
{ |
|
struct hrtimer_sleeper timeout, *to; |
|
struct rt_mutex_waiter rt_waiter; |
|
struct futex_hash_bucket *hb; |
|
union futex_key key2 = FUTEX_KEY_INIT; |
|
struct futex_q q = futex_q_init; |
|
struct rt_mutex_base *pi_mutex; |
|
int res, ret; |
|
|
|
if (!IS_ENABLED(CONFIG_FUTEX_PI)) |
|
return -ENOSYS; |
|
|
|
if (uaddr == uaddr2) |
|
return -EINVAL; |
|
|
|
if (!bitset) |
|
return -EINVAL; |
|
|
|
to = futex_setup_timer(abs_time, &timeout, flags, |
|
current->timer_slack_ns); |
|
|
|
/* |
|
* The waiter is allocated on our stack, manipulated by the requeue |
|
* code while we sleep on uaddr. |
|
*/ |
|
rt_mutex_init_waiter(&rt_waiter); |
|
|
|
ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, FUTEX_WRITE); |
|
if (unlikely(ret != 0)) |
|
goto out; |
|
|
|
q.bitset = bitset; |
|
q.rt_waiter = &rt_waiter; |
|
q.requeue_pi_key = &key2; |
|
|
|
/* |
|
* Prepare to wait on uaddr. On success, it holds hb->lock and q |
|
* is initialized. |
|
*/ |
|
ret = futex_wait_setup(uaddr, val, flags, &q, &hb); |
|
if (ret) |
|
goto out; |
|
|
|
/* |
|
* The check above which compares uaddrs is not sufficient for |
|
* shared futexes. We need to compare the keys: |
|
*/ |
|
if (match_futex(&q.key, &key2)) { |
|
queue_unlock(hb); |
|
ret = -EINVAL; |
|
goto out; |
|
} |
|
|
|
/* Queue the futex_q, drop the hb lock, wait for wakeup. */ |
|
futex_wait_queue_me(hb, &q, to); |
|
|
|
switch (futex_requeue_pi_wakeup_sync(&q)) { |
|
case Q_REQUEUE_PI_IGNORE: |
|
/* The waiter is still on uaddr1 */ |
|
spin_lock(&hb->lock); |
|
ret = handle_early_requeue_pi_wakeup(hb, &q, to); |
|
spin_unlock(&hb->lock); |
|
break; |
|
|
|
case Q_REQUEUE_PI_LOCKED: |
|
/* The requeue acquired the lock */ |
|
if (q.pi_state && (q.pi_state->owner != current)) { |
|
spin_lock(q.lock_ptr); |
|
ret = fixup_owner(uaddr2, &q, true); |
|
/* |
|
* Drop the reference to the pi state which the |
|
* requeue_pi() code acquired for us. |
|
*/ |
|
put_pi_state(q.pi_state); |
|
spin_unlock(q.lock_ptr); |
|
/* |
|
* Adjust the return value. It's either -EFAULT or |
|
* success (1) but the caller expects 0 for success. |
|
*/ |
|
ret = ret < 0 ? ret : 0; |
|
} |
|
break; |
|
|
|
case Q_REQUEUE_PI_DONE: |
|
/* Requeue completed. Current is 'pi_blocked_on' the rtmutex */ |
|
pi_mutex = &q.pi_state->pi_mutex; |
|
ret = rt_mutex_wait_proxy_lock(pi_mutex, to, &rt_waiter); |
|
|
|
/* Current is not longer pi_blocked_on */ |
|
spin_lock(q.lock_ptr); |
|
if (ret && !rt_mutex_cleanup_proxy_lock(pi_mutex, &rt_waiter)) |
|
ret = 0; |
|
|
|
debug_rt_mutex_free_waiter(&rt_waiter); |
|
/* |
|
* Fixup the pi_state owner and possibly acquire the lock if we |
|
* haven't already. |
|
*/ |
|
res = fixup_owner(uaddr2, &q, !ret); |
|
/* |
|
* If fixup_owner() returned an error, propagate that. If it |
|
* acquired the lock, clear -ETIMEDOUT or -EINTR. |
|
*/ |
|
if (res) |
|
ret = (res < 0) ? res : 0; |
|
|
|
unqueue_me_pi(&q); |
|
spin_unlock(q.lock_ptr); |
|
|
|
if (ret == -EINTR) { |
|
/* |
|
* We've already been requeued, but cannot restart |
|
* by calling futex_lock_pi() directly. We could |
|
* restart this syscall, but it would detect that |
|
* the user space "val" changed and return |
|
* -EWOULDBLOCK. Save the overhead of the restart |
|
* and return -EWOULDBLOCK directly. |
|
*/ |
|
ret = -EWOULDBLOCK; |
|
} |
|
break; |
|
default: |
|
BUG(); |
|
} |
|
|
|
out: |
|
if (to) { |
|
hrtimer_cancel(&to->timer); |
|
destroy_hrtimer_on_stack(&to->timer); |
|
} |
|
return ret; |
|
} |
|
|
|
/* |
|
* Support for robust futexes: the kernel cleans up held futexes at |
|
* thread exit time. |
|
* |
|
* Implementation: user-space maintains a per-thread list of locks it |
|
* is holding. Upon do_exit(), the kernel carefully walks this list, |
|
* and marks all locks that are owned by this thread with the |
|
* FUTEX_OWNER_DIED bit, and wakes up a waiter (if any). The list is |
|
* always manipulated with the lock held, so the list is private and |
|
* per-thread. Userspace also maintains a per-thread 'list_op_pending' |
|
* field, to allow the kernel to clean up if the thread dies after |
|
* acquiring the lock, but just before it could have added itself to |
|
* the list. There can only be one such pending lock. |
|
*/ |
|
|
|
/** |
|
* sys_set_robust_list() - Set the robust-futex list head of a task |
|
* @head: pointer to the list-head |
|
* @len: length of the list-head, as userspace expects |
|
*/ |
|
SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head, |
|
size_t, len) |
|
{ |
|
if (!futex_cmpxchg_enabled) |
|
return -ENOSYS; |
|
/* |
|
* The kernel knows only one size for now: |
|
*/ |
|
if (unlikely(len != sizeof(*head))) |
|
return -EINVAL; |
|
|
|
current->robust_list = head; |
|
|
|
return 0; |
|
} |
|
|
|
/** |
|
* sys_get_robust_list() - Get the robust-futex list head of a task |
|
* @pid: pid of the process [zero for current task] |
|
* @head_ptr: pointer to a list-head pointer, the kernel fills it in |
|
* @len_ptr: pointer to a length field, the kernel fills in the header size |
|
*/ |
|
SYSCALL_DEFINE3(get_robust_list, int, pid, |
|
struct robust_list_head __user * __user *, head_ptr, |
|
size_t __user *, len_ptr) |
|
{ |
|
struct robust_list_head __user *head; |
|
unsigned long ret; |
|
struct task_struct *p; |
|
|
|
if (!futex_cmpxchg_enabled) |
|
return -ENOSYS; |
|
|
|
rcu_read_lock(); |
|
|
|
ret = -ESRCH; |
|
if (!pid) |
|
p = current; |
|
else { |
|
p = find_task_by_vpid(pid); |
|
if (!p) |
|
goto err_unlock; |
|
} |
|
|
|
ret = -EPERM; |
|
if (!ptrace_may_access(p, PTRACE_MODE_READ_REALCREDS)) |
|
goto err_unlock; |
|
|
|
head = p->robust_list; |
|
rcu_read_unlock(); |
|
|
|
if (put_user(sizeof(*head), len_ptr)) |
|
return -EFAULT; |
|
return put_user(head, head_ptr); |
|
|
|
err_unlock: |
|
rcu_read_unlock(); |
|
|
|
return ret; |
|
} |
|
|
|
/* Constants for the pending_op argument of handle_futex_death */ |
|
#define HANDLE_DEATH_PENDING true |
|
#define HANDLE_DEATH_LIST false |
|
|
|
/* |
|
* Process a futex-list entry, check whether it's owned by the |
|
* dying task, and do notification if so: |
|
*/ |
|
static int handle_futex_death(u32 __user *uaddr, struct task_struct *curr, |
|
bool pi, bool pending_op) |
|
{ |
|
u32 uval, nval, mval; |
|
int err; |
|
|
|
/* Futex address must be 32bit aligned */ |
|
if ((((unsigned long)uaddr) % sizeof(*uaddr)) != 0) |
|
return -1; |
|
|
|
retry: |
|
if (get_user(uval, uaddr)) |
|
return -1; |
|
|
|
/* |
|
* Special case for regular (non PI) futexes. The unlock path in |
|
* user space has two race scenarios: |
|
* |
|
* 1. The unlock path releases the user space futex value and |
|
* before it can execute the futex() syscall to wake up |
|
* waiters it is killed. |
|
* |
|
* 2. A woken up waiter is killed before it can acquire the |
|
* futex in user space. |
|
* |
|
* In both cases the TID validation below prevents a wakeup of |
|
* potential waiters which can cause these waiters to block |
|
* forever. |
|
* |
|
* In both cases the following conditions are met: |
|
* |
|
* 1) task->robust_list->list_op_pending != NULL |
|
* @pending_op == true |
|
* 2) User space futex value == 0 |
|
* 3) Regular futex: @pi == false |
|
* |
|
* If these conditions are met, it is safe to attempt waking up a |
|
* potential waiter without touching the user space futex value and |
|
* trying to set the OWNER_DIED bit. The user space futex value is |
|
* uncontended and the rest of the user space mutex state is |
|
* consistent, so a woken waiter will just take over the |
|
* uncontended futex. Setting the OWNER_DIED bit would create |
|
* inconsistent state and malfunction of the user space owner died |
|
* handling. |
|
*/ |
|
if (pending_op && !pi && !uval) { |
|
futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY); |
|
return 0; |
|
} |
|
|
|
if ((uval & FUTEX_TID_MASK) != task_pid_vnr(curr)) |
|
return 0; |
|
|
|
/* |
|
* Ok, this dying thread is truly holding a futex |
|
* of interest. Set the OWNER_DIED bit atomically |
|
* via cmpxchg, and if the value had FUTEX_WAITERS |
|
* set, wake up a waiter (if any). (We have to do a |
|
* futex_wake() even if OWNER_DIED is already set - |
|
* to handle the rare but possible case of recursive |
|
* thread-death.) The rest of the cleanup is done in |
|
* userspace. |
|
*/ |
|
mval = (uval & FUTEX_WAITERS) | FUTEX_OWNER_DIED; |
|
|
|
/* |
|
* We are not holding a lock here, but we want to have |
|
* the pagefault_disable/enable() protection because |
|
* we want to handle the fault gracefully. If the |
|
* access fails we try to fault in the futex with R/W |
|
* verification via get_user_pages. get_user() above |
|
* does not guarantee R/W access. If that fails we |
|
* give up and leave the futex locked. |
|
*/ |
|
if ((err = cmpxchg_futex_value_locked(&nval, uaddr, uval, mval))) { |
|
switch (err) { |
|
case -EFAULT: |
|
if (fault_in_user_writeable(uaddr)) |
|
return -1; |
|
goto retry; |
|
|
|
case -EAGAIN: |
|
cond_resched(); |
|
goto retry; |
|
|
|
default: |
|
WARN_ON_ONCE(1); |
|
return err; |
|
} |
|
} |
|
|
|
if (nval != uval) |
|
goto retry; |
|
|
|
/* |
|
* Wake robust non-PI futexes here. The wakeup of |
|
* PI futexes happens in exit_pi_state(): |
|
*/ |
|
if (!pi && (uval & FUTEX_WAITERS)) |
|
futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY); |
|
|
|
return 0; |
|
} |
|
|
|
/* |
|
* Fetch a robust-list pointer. Bit 0 signals PI futexes: |
|
*/ |
|
static inline int fetch_robust_entry(struct robust_list __user **entry, |
|
struct robust_list __user * __user *head, |
|
unsigned int *pi) |
|
{ |
|
unsigned long uentry; |
|
|
|
if (get_user(uentry, (unsigned long __user *)head)) |
|
return -EFAULT; |
|
|
|
*entry = (void __user *)(uentry & ~1UL); |
|
*pi = uentry & 1; |
|
|
|
return 0; |
|
} |
|
|
|
/* |
|
* Walk curr->robust_list (very carefully, it's a userspace list!) |
|
* and mark any locks found there dead, and notify any waiters. |
|
* |
|
* We silently return on any sign of list-walking problem. |
|
*/ |
|
static void exit_robust_list(struct task_struct *curr) |
|
{ |
|
struct robust_list_head __user *head = curr->robust_list; |
|
struct robust_list __user *entry, *next_entry, *pending; |
|
unsigned int limit = ROBUST_LIST_LIMIT, pi, pip; |
|
unsigned int next_pi; |
|
unsigned long futex_offset; |
|
int rc; |
|
|
|
if (!futex_cmpxchg_enabled) |
|
return; |
|
|
|
/* |
|
* Fetch the list head (which was registered earlier, via |
|
* sys_set_robust_list()): |
|
*/ |
|
if (fetch_robust_entry(&entry, &head->list.next, &pi)) |
|
return; |
|
/* |
|
* Fetch the relative futex offset: |
|
*/ |
|
if (get_user(futex_offset, &head->futex_offset)) |
|
return; |
|
/* |
|
* Fetch any possibly pending lock-add first, and handle it |
|
* if it exists: |
|
*/ |
|
if (fetch_robust_entry(&pending, &head->list_op_pending, &pip)) |
|
return; |
|
|
|
next_entry = NULL; /* avoid warning with gcc */ |
|
while (entry != &head->list) { |
|
/* |
|
* Fetch the next entry in the list before calling |
|
* handle_futex_death: |
|
*/ |
|
rc = fetch_robust_entry(&next_entry, &entry->next, &next_pi); |
|
/* |
|
* A pending lock might already be on the list, so |
|
* don't process it twice: |
|
*/ |
|
if (entry != pending) { |
|
if (handle_futex_death((void __user *)entry + futex_offset, |
|
curr, pi, HANDLE_DEATH_LIST)) |
|
return; |
|
} |
|
if (rc) |
|
return; |
|
entry = next_entry; |
|
pi = next_pi; |
|
/* |
|
* Avoid excessively long or circular lists: |
|
*/ |
|
if (!--limit) |
|
break; |
|
|
|
cond_resched(); |
|
} |
|
|
|
if (pending) { |
|
handle_futex_death((void __user *)pending + futex_offset, |
|
curr, pip, HANDLE_DEATH_PENDING); |
|
} |
|
} |
|
|
|
static void futex_cleanup(struct task_struct *tsk) |
|
{ |
|
if (unlikely(tsk->robust_list)) { |
|
exit_robust_list(tsk); |
|
tsk->robust_list = NULL; |
|
} |
|
|
|
#ifdef CONFIG_COMPAT |
|
if (unlikely(tsk->compat_robust_list)) { |
|
compat_exit_robust_list(tsk); |
|
tsk->compat_robust_list = NULL; |
|
} |
|
#endif |
|
|
|
if (unlikely(!list_empty(&tsk->pi_state_list))) |
|
exit_pi_state_list(tsk); |
|
} |
|
|
|
/** |
|
* futex_exit_recursive - Set the tasks futex state to FUTEX_STATE_DEAD |
|
* @tsk: task to set the state on |
|
* |
|
* Set the futex exit state of the task lockless. The futex waiter code |
|
* observes that state when a task is exiting and loops until the task has |
|
* actually finished the futex cleanup. The worst case for this is that the |
|
* waiter runs through the wait loop until the state becomes visible. |
|
* |
|
* This is called from the recursive fault handling path in do_exit(). |
|
* |
|
* This is best effort. Either the futex exit code has run already or |
|
* not. If the OWNER_DIED bit has been set on the futex then the waiter can |
|
* take it over. If not, the problem is pushed back to user space. If the |
|
* futex exit code did not run yet, then an already queued waiter might |
|
* block forever, but there is nothing which can be done about that. |
|
*/ |
|
void futex_exit_recursive(struct task_struct *tsk) |
|
{ |
|
/* If the state is FUTEX_STATE_EXITING then futex_exit_mutex is held */ |
|
if (tsk->futex_state == FUTEX_STATE_EXITING) |
|
mutex_unlock(&tsk->futex_exit_mutex); |
|
tsk->futex_state = FUTEX_STATE_DEAD; |
|
} |
|
|
|
static void futex_cleanup_begin(struct task_struct *tsk) |
|
{ |
|
/* |
|
* Prevent various race issues against a concurrent incoming waiter |
|
* including live locks by forcing the waiter to block on |
|
* tsk->futex_exit_mutex when it observes FUTEX_STATE_EXITING in |
|
* attach_to_pi_owner(). |
|
*/ |
|
mutex_lock(&tsk->futex_exit_mutex); |
|
|
|
/* |
|
* Switch the state to FUTEX_STATE_EXITING under tsk->pi_lock. |
|
* |
|
* This ensures that all subsequent checks of tsk->futex_state in |
|
* attach_to_pi_owner() must observe FUTEX_STATE_EXITING with |
|
* tsk->pi_lock held. |
|
* |
|
* It guarantees also that a pi_state which was queued right before |
|
* the state change under tsk->pi_lock by a concurrent waiter must |
|
* be observed in exit_pi_state_list(). |
|
*/ |
|
raw_spin_lock_irq(&tsk->pi_lock); |
|
tsk->futex_state = FUTEX_STATE_EXITING; |
|
raw_spin_unlock_irq(&tsk->pi_lock); |
|
} |
|
|
|
static void futex_cleanup_end(struct task_struct *tsk, int state) |
|
{ |
|
/* |
|
* Lockless store. The only side effect is that an observer might |
|
* take another loop until it becomes visible. |
|
*/ |
|
tsk->futex_state = state; |
|
/* |
|
* Drop the exit protection. This unblocks waiters which observed |
|
* FUTEX_STATE_EXITING to reevaluate the state. |
|
*/ |
|
mutex_unlock(&tsk->futex_exit_mutex); |
|
} |
|
|
|
void futex_exec_release(struct task_struct *tsk) |
|
{ |
|
/* |
|
* The state handling is done for consistency, but in the case of |
|
* exec() there is no way to prevent further damage as the PID stays |
|
* the same. But for the unlikely and arguably buggy case that a |
|
* futex is held on exec(), this provides at least as much state |
|
* consistency protection which is possible. |
|
*/ |
|
futex_cleanup_begin(tsk); |
|
futex_cleanup(tsk); |
|
/* |
|
* Reset the state to FUTEX_STATE_OK. The task is alive and about |
|
* exec a new binary. |
|
*/ |
|
futex_cleanup_end(tsk, FUTEX_STATE_OK); |
|
} |
|
|
|
void futex_exit_release(struct task_struct *tsk) |
|
{ |
|
futex_cleanup_begin(tsk); |
|
futex_cleanup(tsk); |
|
futex_cleanup_end(tsk, FUTEX_STATE_DEAD); |
|
} |
|
|
|
long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout, |
|
u32 __user *uaddr2, u32 val2, u32 val3) |
|
{ |
|
int cmd = op & FUTEX_CMD_MASK; |
|
unsigned int flags = 0; |
|
|
|
if (!(op & FUTEX_PRIVATE_FLAG)) |
|
flags |= FLAGS_SHARED; |
|
|
|
if (op & FUTEX_CLOCK_REALTIME) { |
|
flags |= FLAGS_CLOCKRT; |
|
if (cmd != FUTEX_WAIT_BITSET && cmd != FUTEX_WAIT_REQUEUE_PI && |
|
cmd != FUTEX_LOCK_PI2) |
|
return -ENOSYS; |
|
} |
|
|
|
switch (cmd) { |
|
case FUTEX_LOCK_PI: |
|
case FUTEX_LOCK_PI2: |
|
case FUTEX_UNLOCK_PI: |
|
case FUTEX_TRYLOCK_PI: |
|
case FUTEX_WAIT_REQUEUE_PI: |
|
case FUTEX_CMP_REQUEUE_PI: |
|
if (!futex_cmpxchg_enabled) |
|
return -ENOSYS; |
|
} |
|
|
|
switch (cmd) { |
|
case FUTEX_WAIT: |
|
val3 = FUTEX_BITSET_MATCH_ANY; |
|
fallthrough; |
|
case FUTEX_WAIT_BITSET: |
|
return futex_wait(uaddr, flags, val, timeout, val3); |
|
case FUTEX_WAKE: |
|
val3 = FUTEX_BITSET_MATCH_ANY; |
|
fallthrough; |
|
case FUTEX_WAKE_BITSET: |
|
return futex_wake(uaddr, flags, val, val3); |
|
case FUTEX_REQUEUE: |
|
return futex_requeue(uaddr, flags, uaddr2, val, val2, NULL, 0); |
|
case FUTEX_CMP_REQUEUE: |
|
return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 0); |
|
case FUTEX_WAKE_OP: |
|
return futex_wake_op(uaddr, flags, uaddr2, val, val2, val3); |
|
case FUTEX_LOCK_PI: |
|
flags |= FLAGS_CLOCKRT; |
|
fallthrough; |
|
case FUTEX_LOCK_PI2: |
|
return futex_lock_pi(uaddr, flags, timeout, 0); |
|
case FUTEX_UNLOCK_PI: |
|
return futex_unlock_pi(uaddr, flags); |
|
case FUTEX_TRYLOCK_PI: |
|
return futex_lock_pi(uaddr, flags, NULL, 1); |
|
case FUTEX_WAIT_REQUEUE_PI: |
|
val3 = FUTEX_BITSET_MATCH_ANY; |
|
return futex_wait_requeue_pi(uaddr, flags, val, timeout, val3, |
|
uaddr2); |
|
case FUTEX_CMP_REQUEUE_PI: |
|
return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 1); |
|
} |
|
return -ENOSYS; |
|
} |
|
|
|
static __always_inline bool futex_cmd_has_timeout(u32 cmd) |
|
{ |
|
switch (cmd) { |
|
case FUTEX_WAIT: |
|
case FUTEX_LOCK_PI: |
|
case FUTEX_LOCK_PI2: |
|
case FUTEX_WAIT_BITSET: |
|
case FUTEX_WAIT_REQUEUE_PI: |
|
return true; |
|
} |
|
return false; |
|
} |
|
|
|
static __always_inline int |
|
futex_init_timeout(u32 cmd, u32 op, struct timespec64 *ts, ktime_t *t) |
|
{ |
|
if (!timespec64_valid(ts)) |
|
return -EINVAL; |
|
|
|
*t = timespec64_to_ktime(*ts); |
|
if (cmd == FUTEX_WAIT) |
|
*t = ktime_add_safe(ktime_get(), *t); |
|
else if (cmd != FUTEX_LOCK_PI && !(op & FUTEX_CLOCK_REALTIME)) |
|
*t = timens_ktime_to_host(CLOCK_MONOTONIC, *t); |
|
return 0; |
|
} |
|
|
|
SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val, |
|
const struct __kernel_timespec __user *, utime, |
|
u32 __user *, uaddr2, u32, val3) |
|
{ |
|
int ret, cmd = op & FUTEX_CMD_MASK; |
|
ktime_t t, *tp = NULL; |
|
struct timespec64 ts; |
|
|
|
if (utime && futex_cmd_has_timeout(cmd)) { |
|
if (unlikely(should_fail_futex(!(op & FUTEX_PRIVATE_FLAG)))) |
|
return -EFAULT; |
|
if (get_timespec64(&ts, utime)) |
|
return -EFAULT; |
|
ret = futex_init_timeout(cmd, op, &ts, &t); |
|
if (ret) |
|
return ret; |
|
tp = &t; |
|
} |
|
|
|
return do_futex(uaddr, op, val, tp, uaddr2, (unsigned long)utime, val3); |
|
} |
|
|
|
#ifdef CONFIG_COMPAT |
|
/* |
|
* Fetch a robust-list pointer. Bit 0 signals PI futexes: |
|
*/ |
|
static inline int |
|
compat_fetch_robust_entry(compat_uptr_t *uentry, struct robust_list __user **entry, |
|
compat_uptr_t __user *head, unsigned int *pi) |
|
{ |
|
if (get_user(*uentry, head)) |
|
return -EFAULT; |
|
|
|
*entry = compat_ptr((*uentry) & ~1); |
|
*pi = (unsigned int)(*uentry) & 1; |
|
|
|
return 0; |
|
} |
|
|
|
static void __user *futex_uaddr(struct robust_list __user *entry, |
|
compat_long_t futex_offset) |
|
{ |
|
compat_uptr_t base = ptr_to_compat(entry); |
|
void __user *uaddr = compat_ptr(base + futex_offset); |
|
|
|
return uaddr; |
|
} |
|
|
|
/* |
|
* Walk curr->robust_list (very carefully, it's a userspace list!) |
|
* and mark any locks found there dead, and notify any waiters. |
|
* |
|
* We silently return on any sign of list-walking problem. |
|
*/ |
|
static void compat_exit_robust_list(struct task_struct *curr) |
|
{ |
|
struct compat_robust_list_head __user *head = curr->compat_robust_list; |
|
struct robust_list __user *entry, *next_entry, *pending; |
|
unsigned int limit = ROBUST_LIST_LIMIT, pi, pip; |
|
unsigned int next_pi; |
|
compat_uptr_t uentry, next_uentry, upending; |
|
compat_long_t futex_offset; |
|
int rc; |
|
|
|
if (!futex_cmpxchg_enabled) |
|
return; |
|
|
|
/* |
|
* Fetch the list head (which was registered earlier, via |
|
* sys_set_robust_list()): |
|
*/ |
|
if (compat_fetch_robust_entry(&uentry, &entry, &head->list.next, &pi)) |
|
return; |
|
/* |
|
* Fetch the relative futex offset: |
|
*/ |
|
if (get_user(futex_offset, &head->futex_offset)) |
|
return; |
|
/* |
|
* Fetch any possibly pending lock-add first, and handle it |
|
* if it exists: |
|
*/ |
|
if (compat_fetch_robust_entry(&upending, &pending, |
|
&head->list_op_pending, &pip)) |
|
return; |
|
|
|
next_entry = NULL; /* avoid warning with gcc */ |
|
while (entry != (struct robust_list __user *) &head->list) { |
|
/* |
|
* Fetch the next entry in the list before calling |
|
* handle_futex_death: |
|
*/ |
|
rc = compat_fetch_robust_entry(&next_uentry, &next_entry, |
|
(compat_uptr_t __user *)&entry->next, &next_pi); |
|
/* |
|
* A pending lock might already be on the list, so |
|
* dont process it twice: |
|
*/ |
|
if (entry != pending) { |
|
void __user *uaddr = futex_uaddr(entry, futex_offset); |
|
|
|
if (handle_futex_death(uaddr, curr, pi, |
|
HANDLE_DEATH_LIST)) |
|
return; |
|
} |
|
if (rc) |
|
return; |
|
uentry = next_uentry; |
|
entry = next_entry; |
|
pi = next_pi; |
|
/* |
|
* Avoid excessively long or circular lists: |
|
*/ |
|
if (!--limit) |
|
break; |
|
|
|
cond_resched(); |
|
} |
|
if (pending) { |
|
void __user *uaddr = futex_uaddr(pending, futex_offset); |
|
|
|
handle_futex_death(uaddr, curr, pip, HANDLE_DEATH_PENDING); |
|
} |
|
} |
|
|
|
COMPAT_SYSCALL_DEFINE2(set_robust_list, |
|
struct compat_robust_list_head __user *, head, |
|
compat_size_t, len) |
|
{ |
|
if (!futex_cmpxchg_enabled) |
|
return -ENOSYS; |
|
|
|
if (unlikely(len != sizeof(*head))) |
|
return -EINVAL; |
|
|
|
current->compat_robust_list = head; |
|
|
|
return 0; |
|
} |
|
|
|
COMPAT_SYSCALL_DEFINE3(get_robust_list, int, pid, |
|
compat_uptr_t __user *, head_ptr, |
|
compat_size_t __user *, len_ptr) |
|
{ |
|
struct compat_robust_list_head __user *head; |
|
unsigned long ret; |
|
struct task_struct *p; |
|
|
|
if (!futex_cmpxchg_enabled) |
|
return -ENOSYS; |
|
|
|
rcu_read_lock(); |
|
|
|
ret = -ESRCH; |
|
if (!pid) |
|
p = current; |
|
else { |
|
p = find_task_by_vpid(pid); |
|
if (!p) |
|
goto err_unlock; |
|
} |
|
|
|
ret = -EPERM; |
|
if (!ptrace_may_access(p, PTRACE_MODE_READ_REALCREDS)) |
|
goto err_unlock; |
|
|
|
head = p->compat_robust_list; |
|
rcu_read_unlock(); |
|
|
|
if (put_user(sizeof(*head), len_ptr)) |
|
return -EFAULT; |
|
return put_user(ptr_to_compat(head), head_ptr); |
|
|
|
err_unlock: |
|
rcu_read_unlock(); |
|
|
|
return ret; |
|
} |
|
#endif /* CONFIG_COMPAT */ |
|
|
|
#ifdef CONFIG_COMPAT_32BIT_TIME |
|
SYSCALL_DEFINE6(futex_time32, u32 __user *, uaddr, int, op, u32, val, |
|
const struct old_timespec32 __user *, utime, u32 __user *, uaddr2, |
|
u32, val3) |
|
{ |
|
int ret, cmd = op & FUTEX_CMD_MASK; |
|
ktime_t t, *tp = NULL; |
|
struct timespec64 ts; |
|
|
|
if (utime && futex_cmd_has_timeout(cmd)) { |
|
if (get_old_timespec32(&ts, utime)) |
|
return -EFAULT; |
|
ret = futex_init_timeout(cmd, op, &ts, &t); |
|
if (ret) |
|
return ret; |
|
tp = &t; |
|
} |
|
|
|
return do_futex(uaddr, op, val, tp, uaddr2, (unsigned long)utime, val3); |
|
} |
|
#endif /* CONFIG_COMPAT_32BIT_TIME */ |
|
|
|
static void __init futex_detect_cmpxchg(void) |
|
{ |
|
#ifndef CONFIG_HAVE_FUTEX_CMPXCHG |
|
u32 curval; |
|
|
|
/* |
|
* This will fail and we want it. Some arch implementations do |
|
* runtime detection of the futex_atomic_cmpxchg_inatomic() |
|
* functionality. We want to know that before we call in any |
|
* of the complex code paths. Also we want to prevent |
|
* registration of robust lists in that case. NULL is |
|
* guaranteed to fault and we get -EFAULT on functional |
|
* implementation, the non-functional ones will return |
|
* -ENOSYS. |
|
*/ |
|
if (cmpxchg_futex_value_locked(&curval, NULL, 0, 0) == -EFAULT) |
|
futex_cmpxchg_enabled = 1; |
|
#endif |
|
} |
|
|
|
static int __init futex_init(void) |
|
{ |
|
unsigned int futex_shift; |
|
unsigned long i; |
|
|
|
#if CONFIG_BASE_SMALL |
|
futex_hashsize = 16; |
|
#else |
|
futex_hashsize = roundup_pow_of_two(256 * num_possible_cpus()); |
|
#endif |
|
|
|
futex_queues = alloc_large_system_hash("futex", sizeof(*futex_queues), |
|
futex_hashsize, 0, |
|
futex_hashsize < 256 ? HASH_SMALL : 0, |
|
&futex_shift, NULL, |
|
futex_hashsize, futex_hashsize); |
|
futex_hashsize = 1UL << futex_shift; |
|
|
|
futex_detect_cmpxchg(); |
|
|
|
for (i = 0; i < futex_hashsize; i++) { |
|
atomic_set(&futex_queues[i].waiters, 0); |
|
plist_head_init(&futex_queues[i].chain); |
|
spin_lock_init(&futex_queues[i].lock); |
|
} |
|
|
|
return 0; |
|
} |
|
core_initcall(futex_init);
|
|
|