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1737 lines
47 KiB
1737 lines
47 KiB
// SPDX-License-Identifier: GPL-2.0-only |
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/* |
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* RT-Mutexes: simple blocking mutual exclusion locks with PI support |
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* |
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* started by Ingo Molnar and Thomas Gleixner. |
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* |
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* Copyright (C) 2004-2006 Red Hat, Inc., Ingo Molnar <[email protected]> |
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* Copyright (C) 2005-2006 Timesys Corp., Thomas Gleixner <[email protected]> |
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* Copyright (C) 2005 Kihon Technologies Inc., Steven Rostedt |
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* Copyright (C) 2006 Esben Nielsen |
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* Adaptive Spinlocks: |
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* Copyright (C) 2008 Novell, Inc., Gregory Haskins, Sven Dietrich, |
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* and Peter Morreale, |
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* Adaptive Spinlocks simplification: |
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* Copyright (C) 2008 Red Hat, Inc., Steven Rostedt <[email protected]> |
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* |
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* See Documentation/locking/rt-mutex-design.rst for details. |
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*/ |
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#include <linux/sched.h> |
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#include <linux/sched/debug.h> |
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#include <linux/sched/deadline.h> |
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#include <linux/sched/signal.h> |
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#include <linux/sched/rt.h> |
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#include <linux/sched/wake_q.h> |
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#include <linux/ww_mutex.h> |
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#include <trace/events/lock.h> |
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#include "rtmutex_common.h" |
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#ifndef WW_RT |
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# define build_ww_mutex() (false) |
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# define ww_container_of(rtm) NULL |
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static inline int __ww_mutex_add_waiter(struct rt_mutex_waiter *waiter, |
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struct rt_mutex *lock, |
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struct ww_acquire_ctx *ww_ctx) |
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{ |
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return 0; |
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} |
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static inline void __ww_mutex_check_waiters(struct rt_mutex *lock, |
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struct ww_acquire_ctx *ww_ctx) |
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{ |
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} |
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static inline void ww_mutex_lock_acquired(struct ww_mutex *lock, |
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struct ww_acquire_ctx *ww_ctx) |
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{ |
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} |
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static inline int __ww_mutex_check_kill(struct rt_mutex *lock, |
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struct rt_mutex_waiter *waiter, |
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struct ww_acquire_ctx *ww_ctx) |
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{ |
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return 0; |
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} |
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#else |
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# define build_ww_mutex() (true) |
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# define ww_container_of(rtm) container_of(rtm, struct ww_mutex, base) |
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# include "ww_mutex.h" |
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#endif |
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/* |
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* lock->owner state tracking: |
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* |
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* lock->owner holds the task_struct pointer of the owner. Bit 0 |
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* is used to keep track of the "lock has waiters" state. |
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* |
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* owner bit0 |
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* NULL 0 lock is free (fast acquire possible) |
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* NULL 1 lock is free and has waiters and the top waiter |
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* is going to take the lock* |
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* taskpointer 0 lock is held (fast release possible) |
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* taskpointer 1 lock is held and has waiters** |
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* |
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* The fast atomic compare exchange based acquire and release is only |
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* possible when bit 0 of lock->owner is 0. |
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* |
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* (*) It also can be a transitional state when grabbing the lock |
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* with ->wait_lock is held. To prevent any fast path cmpxchg to the lock, |
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* we need to set the bit0 before looking at the lock, and the owner may be |
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* NULL in this small time, hence this can be a transitional state. |
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* |
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* (**) There is a small time when bit 0 is set but there are no |
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* waiters. This can happen when grabbing the lock in the slow path. |
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* To prevent a cmpxchg of the owner releasing the lock, we need to |
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* set this bit before looking at the lock. |
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*/ |
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static __always_inline void |
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rt_mutex_set_owner(struct rt_mutex_base *lock, struct task_struct *owner) |
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{ |
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unsigned long val = (unsigned long)owner; |
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if (rt_mutex_has_waiters(lock)) |
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val |= RT_MUTEX_HAS_WAITERS; |
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WRITE_ONCE(lock->owner, (struct task_struct *)val); |
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} |
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static __always_inline void clear_rt_mutex_waiters(struct rt_mutex_base *lock) |
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{ |
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lock->owner = (struct task_struct *) |
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((unsigned long)lock->owner & ~RT_MUTEX_HAS_WAITERS); |
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} |
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static __always_inline void fixup_rt_mutex_waiters(struct rt_mutex_base *lock) |
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{ |
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unsigned long owner, *p = (unsigned long *) &lock->owner; |
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|
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if (rt_mutex_has_waiters(lock)) |
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return; |
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/* |
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* The rbtree has no waiters enqueued, now make sure that the |
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* lock->owner still has the waiters bit set, otherwise the |
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* following can happen: |
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* |
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* CPU 0 CPU 1 CPU2 |
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* l->owner=T1 |
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* rt_mutex_lock(l) |
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* lock(l->lock) |
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* l->owner = T1 | HAS_WAITERS; |
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* enqueue(T2) |
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* boost() |
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* unlock(l->lock) |
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* block() |
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* |
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* rt_mutex_lock(l) |
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* lock(l->lock) |
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* l->owner = T1 | HAS_WAITERS; |
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* enqueue(T3) |
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* boost() |
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* unlock(l->lock) |
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* block() |
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* signal(->T2) signal(->T3) |
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* lock(l->lock) |
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* dequeue(T2) |
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* deboost() |
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* unlock(l->lock) |
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* lock(l->lock) |
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* dequeue(T3) |
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* ==> wait list is empty |
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* deboost() |
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* unlock(l->lock) |
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* lock(l->lock) |
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* fixup_rt_mutex_waiters() |
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* if (wait_list_empty(l) { |
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* l->owner = owner |
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* owner = l->owner & ~HAS_WAITERS; |
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* ==> l->owner = T1 |
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* } |
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* lock(l->lock) |
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* rt_mutex_unlock(l) fixup_rt_mutex_waiters() |
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* if (wait_list_empty(l) { |
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* owner = l->owner & ~HAS_WAITERS; |
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* cmpxchg(l->owner, T1, NULL) |
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* ===> Success (l->owner = NULL) |
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* |
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* l->owner = owner |
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* ==> l->owner = T1 |
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* } |
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* |
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* With the check for the waiter bit in place T3 on CPU2 will not |
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* overwrite. All tasks fiddling with the waiters bit are |
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* serialized by l->lock, so nothing else can modify the waiters |
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* bit. If the bit is set then nothing can change l->owner either |
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* so the simple RMW is safe. The cmpxchg() will simply fail if it |
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* happens in the middle of the RMW because the waiters bit is |
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* still set. |
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*/ |
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owner = READ_ONCE(*p); |
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if (owner & RT_MUTEX_HAS_WAITERS) |
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WRITE_ONCE(*p, owner & ~RT_MUTEX_HAS_WAITERS); |
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} |
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/* |
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* We can speed up the acquire/release, if there's no debugging state to be |
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* set up. |
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*/ |
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#ifndef CONFIG_DEBUG_RT_MUTEXES |
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static __always_inline bool rt_mutex_cmpxchg_acquire(struct rt_mutex_base *lock, |
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struct task_struct *old, |
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struct task_struct *new) |
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{ |
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return try_cmpxchg_acquire(&lock->owner, &old, new); |
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} |
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static __always_inline bool rt_mutex_cmpxchg_release(struct rt_mutex_base *lock, |
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struct task_struct *old, |
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struct task_struct *new) |
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{ |
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return try_cmpxchg_release(&lock->owner, &old, new); |
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} |
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/* |
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* Callers must hold the ->wait_lock -- which is the whole purpose as we force |
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* all future threads that attempt to [Rmw] the lock to the slowpath. As such |
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* relaxed semantics suffice. |
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*/ |
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static __always_inline void mark_rt_mutex_waiters(struct rt_mutex_base *lock) |
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{ |
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unsigned long owner, *p = (unsigned long *) &lock->owner; |
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do { |
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owner = *p; |
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} while (cmpxchg_relaxed(p, owner, |
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owner | RT_MUTEX_HAS_WAITERS) != owner); |
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} |
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/* |
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* Safe fastpath aware unlock: |
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* 1) Clear the waiters bit |
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* 2) Drop lock->wait_lock |
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* 3) Try to unlock the lock with cmpxchg |
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*/ |
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static __always_inline bool unlock_rt_mutex_safe(struct rt_mutex_base *lock, |
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unsigned long flags) |
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__releases(lock->wait_lock) |
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{ |
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struct task_struct *owner = rt_mutex_owner(lock); |
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clear_rt_mutex_waiters(lock); |
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raw_spin_unlock_irqrestore(&lock->wait_lock, flags); |
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/* |
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* If a new waiter comes in between the unlock and the cmpxchg |
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* we have two situations: |
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* |
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* unlock(wait_lock); |
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* lock(wait_lock); |
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* cmpxchg(p, owner, 0) == owner |
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* mark_rt_mutex_waiters(lock); |
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* acquire(lock); |
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* or: |
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* |
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* unlock(wait_lock); |
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* lock(wait_lock); |
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* mark_rt_mutex_waiters(lock); |
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* |
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* cmpxchg(p, owner, 0) != owner |
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* enqueue_waiter(); |
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* unlock(wait_lock); |
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* lock(wait_lock); |
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* wake waiter(); |
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* unlock(wait_lock); |
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* lock(wait_lock); |
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* acquire(lock); |
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*/ |
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return rt_mutex_cmpxchg_release(lock, owner, NULL); |
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} |
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#else |
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static __always_inline bool rt_mutex_cmpxchg_acquire(struct rt_mutex_base *lock, |
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struct task_struct *old, |
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struct task_struct *new) |
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{ |
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return false; |
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} |
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static __always_inline bool rt_mutex_cmpxchg_release(struct rt_mutex_base *lock, |
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struct task_struct *old, |
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struct task_struct *new) |
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{ |
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return false; |
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} |
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static __always_inline void mark_rt_mutex_waiters(struct rt_mutex_base *lock) |
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{ |
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lock->owner = (struct task_struct *) |
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((unsigned long)lock->owner | RT_MUTEX_HAS_WAITERS); |
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} |
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/* |
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* Simple slow path only version: lock->owner is protected by lock->wait_lock. |
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*/ |
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static __always_inline bool unlock_rt_mutex_safe(struct rt_mutex_base *lock, |
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unsigned long flags) |
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__releases(lock->wait_lock) |
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{ |
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lock->owner = NULL; |
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raw_spin_unlock_irqrestore(&lock->wait_lock, flags); |
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return true; |
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} |
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#endif |
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static __always_inline int __waiter_prio(struct task_struct *task) |
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{ |
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int prio = task->prio; |
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if (!rt_prio(prio)) |
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return DEFAULT_PRIO; |
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return prio; |
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} |
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static __always_inline void |
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waiter_update_prio(struct rt_mutex_waiter *waiter, struct task_struct *task) |
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{ |
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waiter->prio = __waiter_prio(task); |
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waiter->deadline = task->dl.deadline; |
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} |
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/* |
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* Only use with rt_mutex_waiter_{less,equal}() |
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*/ |
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#define task_to_waiter(p) \ |
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&(struct rt_mutex_waiter){ .prio = __waiter_prio(p), .deadline = (p)->dl.deadline } |
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static __always_inline int rt_mutex_waiter_less(struct rt_mutex_waiter *left, |
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struct rt_mutex_waiter *right) |
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{ |
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if (left->prio < right->prio) |
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return 1; |
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/* |
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* If both waiters have dl_prio(), we check the deadlines of the |
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* associated tasks. |
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* If left waiter has a dl_prio(), and we didn't return 1 above, |
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* then right waiter has a dl_prio() too. |
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*/ |
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if (dl_prio(left->prio)) |
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return dl_time_before(left->deadline, right->deadline); |
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return 0; |
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} |
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static __always_inline int rt_mutex_waiter_equal(struct rt_mutex_waiter *left, |
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struct rt_mutex_waiter *right) |
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{ |
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if (left->prio != right->prio) |
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return 0; |
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/* |
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* If both waiters have dl_prio(), we check the deadlines of the |
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* associated tasks. |
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* If left waiter has a dl_prio(), and we didn't return 0 above, |
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* then right waiter has a dl_prio() too. |
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*/ |
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if (dl_prio(left->prio)) |
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return left->deadline == right->deadline; |
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return 1; |
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} |
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static inline bool rt_mutex_steal(struct rt_mutex_waiter *waiter, |
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struct rt_mutex_waiter *top_waiter) |
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{ |
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if (rt_mutex_waiter_less(waiter, top_waiter)) |
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return true; |
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#ifdef RT_MUTEX_BUILD_SPINLOCKS |
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/* |
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* Note that RT tasks are excluded from same priority (lateral) |
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* steals to prevent the introduction of an unbounded latency. |
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*/ |
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if (rt_prio(waiter->prio) || dl_prio(waiter->prio)) |
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return false; |
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return rt_mutex_waiter_equal(waiter, top_waiter); |
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#else |
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return false; |
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#endif |
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} |
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#define __node_2_waiter(node) \ |
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rb_entry((node), struct rt_mutex_waiter, tree_entry) |
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static __always_inline bool __waiter_less(struct rb_node *a, const struct rb_node *b) |
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{ |
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struct rt_mutex_waiter *aw = __node_2_waiter(a); |
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struct rt_mutex_waiter *bw = __node_2_waiter(b); |
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if (rt_mutex_waiter_less(aw, bw)) |
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return 1; |
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if (!build_ww_mutex()) |
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return 0; |
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if (rt_mutex_waiter_less(bw, aw)) |
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return 0; |
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/* NOTE: relies on waiter->ww_ctx being set before insertion */ |
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if (aw->ww_ctx) { |
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if (!bw->ww_ctx) |
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return 1; |
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return (signed long)(aw->ww_ctx->stamp - |
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bw->ww_ctx->stamp) < 0; |
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} |
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return 0; |
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} |
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static __always_inline void |
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rt_mutex_enqueue(struct rt_mutex_base *lock, struct rt_mutex_waiter *waiter) |
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{ |
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rb_add_cached(&waiter->tree_entry, &lock->waiters, __waiter_less); |
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} |
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static __always_inline void |
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rt_mutex_dequeue(struct rt_mutex_base *lock, struct rt_mutex_waiter *waiter) |
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{ |
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if (RB_EMPTY_NODE(&waiter->tree_entry)) |
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return; |
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rb_erase_cached(&waiter->tree_entry, &lock->waiters); |
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RB_CLEAR_NODE(&waiter->tree_entry); |
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} |
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#define __node_2_pi_waiter(node) \ |
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rb_entry((node), struct rt_mutex_waiter, pi_tree_entry) |
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static __always_inline bool |
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__pi_waiter_less(struct rb_node *a, const struct rb_node *b) |
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{ |
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return rt_mutex_waiter_less(__node_2_pi_waiter(a), __node_2_pi_waiter(b)); |
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} |
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static __always_inline void |
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rt_mutex_enqueue_pi(struct task_struct *task, struct rt_mutex_waiter *waiter) |
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{ |
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rb_add_cached(&waiter->pi_tree_entry, &task->pi_waiters, __pi_waiter_less); |
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} |
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static __always_inline void |
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rt_mutex_dequeue_pi(struct task_struct *task, struct rt_mutex_waiter *waiter) |
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{ |
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if (RB_EMPTY_NODE(&waiter->pi_tree_entry)) |
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return; |
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rb_erase_cached(&waiter->pi_tree_entry, &task->pi_waiters); |
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RB_CLEAR_NODE(&waiter->pi_tree_entry); |
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} |
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static __always_inline void rt_mutex_adjust_prio(struct task_struct *p) |
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{ |
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struct task_struct *pi_task = NULL; |
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lockdep_assert_held(&p->pi_lock); |
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if (task_has_pi_waiters(p)) |
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pi_task = task_top_pi_waiter(p)->task; |
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rt_mutex_setprio(p, pi_task); |
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} |
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/* RT mutex specific wake_q wrappers */ |
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static __always_inline void rt_mutex_wake_q_add_task(struct rt_wake_q_head *wqh, |
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struct task_struct *task, |
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unsigned int wake_state) |
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{ |
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if (IS_ENABLED(CONFIG_PREEMPT_RT) && wake_state == TASK_RTLOCK_WAIT) { |
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if (IS_ENABLED(CONFIG_PROVE_LOCKING)) |
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WARN_ON_ONCE(wqh->rtlock_task); |
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get_task_struct(task); |
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wqh->rtlock_task = task; |
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} else { |
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wake_q_add(&wqh->head, task); |
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} |
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} |
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static __always_inline void rt_mutex_wake_q_add(struct rt_wake_q_head *wqh, |
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struct rt_mutex_waiter *w) |
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{ |
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rt_mutex_wake_q_add_task(wqh, w->task, w->wake_state); |
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} |
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static __always_inline void rt_mutex_wake_up_q(struct rt_wake_q_head *wqh) |
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{ |
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if (IS_ENABLED(CONFIG_PREEMPT_RT) && wqh->rtlock_task) { |
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wake_up_state(wqh->rtlock_task, TASK_RTLOCK_WAIT); |
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put_task_struct(wqh->rtlock_task); |
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wqh->rtlock_task = NULL; |
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} |
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if (!wake_q_empty(&wqh->head)) |
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wake_up_q(&wqh->head); |
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|
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/* Pairs with preempt_disable() in mark_wakeup_next_waiter() */ |
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preempt_enable(); |
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} |
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/* |
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* Deadlock detection is conditional: |
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* |
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* If CONFIG_DEBUG_RT_MUTEXES=n, deadlock detection is only conducted |
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* if the detect argument is == RT_MUTEX_FULL_CHAINWALK. |
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* |
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* If CONFIG_DEBUG_RT_MUTEXES=y, deadlock detection is always |
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* conducted independent of the detect argument. |
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* |
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* If the waiter argument is NULL this indicates the deboost path and |
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* deadlock detection is disabled independent of the detect argument |
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* and the config settings. |
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*/ |
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static __always_inline bool |
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rt_mutex_cond_detect_deadlock(struct rt_mutex_waiter *waiter, |
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enum rtmutex_chainwalk chwalk) |
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{ |
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if (IS_ENABLED(CONFIG_DEBUG_RT_MUTEXES)) |
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return waiter != NULL; |
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return chwalk == RT_MUTEX_FULL_CHAINWALK; |
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} |
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static __always_inline struct rt_mutex_base *task_blocked_on_lock(struct task_struct *p) |
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{ |
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return p->pi_blocked_on ? p->pi_blocked_on->lock : NULL; |
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} |
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|
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/* |
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* Adjust the priority chain. Also used for deadlock detection. |
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* Decreases task's usage by one - may thus free the task. |
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* |
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* @task: the task owning the mutex (owner) for which a chain walk is |
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* probably needed |
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* @chwalk: do we have to carry out deadlock detection? |
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* @orig_lock: the mutex (can be NULL if we are walking the chain to recheck |
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* things for a task that has just got its priority adjusted, and |
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* is waiting on a mutex) |
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* @next_lock: the mutex on which the owner of @orig_lock was blocked before |
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* we dropped its pi_lock. Is never dereferenced, only used for |
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* comparison to detect lock chain changes. |
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* @orig_waiter: rt_mutex_waiter struct for the task that has just donated |
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* its priority to the mutex owner (can be NULL in the case |
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* depicted above or if the top waiter is gone away and we are |
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* actually deboosting the owner) |
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* @top_task: the current top waiter |
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* |
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* Returns 0 or -EDEADLK. |
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* |
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* Chain walk basics and protection scope |
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* |
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* [R] refcount on task |
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* [P] task->pi_lock held |
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* [L] rtmutex->wait_lock held |
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* |
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* Step Description Protected by |
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* function arguments: |
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* @task [R] |
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* @orig_lock if != NULL @top_task is blocked on it |
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* @next_lock Unprotected. Cannot be |
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* dereferenced. Only used for |
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* comparison. |
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* @orig_waiter if != NULL @top_task is blocked on it |
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* @top_task current, or in case of proxy |
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* locking protected by calling |
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* code |
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* again: |
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* loop_sanity_check(); |
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* retry: |
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* [1] lock(task->pi_lock); [R] acquire [P] |
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* [2] waiter = task->pi_blocked_on; [P] |
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* [3] check_exit_conditions_1(); [P] |
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* [4] lock = waiter->lock; [P] |
|
* [5] if (!try_lock(lock->wait_lock)) { [P] try to acquire [L] |
|
* unlock(task->pi_lock); release [P] |
|
* goto retry; |
|
* } |
|
* [6] check_exit_conditions_2(); [P] + [L] |
|
* [7] requeue_lock_waiter(lock, waiter); [P] + [L] |
|
* [8] unlock(task->pi_lock); release [P] |
|
* put_task_struct(task); release [R] |
|
* [9] check_exit_conditions_3(); [L] |
|
* [10] task = owner(lock); [L] |
|
* get_task_struct(task); [L] acquire [R] |
|
* lock(task->pi_lock); [L] acquire [P] |
|
* [11] requeue_pi_waiter(tsk, waiters(lock));[P] + [L] |
|
* [12] check_exit_conditions_4(); [P] + [L] |
|
* [13] unlock(task->pi_lock); release [P] |
|
* unlock(lock->wait_lock); release [L] |
|
* goto again; |
|
*/ |
|
static int __sched rt_mutex_adjust_prio_chain(struct task_struct *task, |
|
enum rtmutex_chainwalk chwalk, |
|
struct rt_mutex_base *orig_lock, |
|
struct rt_mutex_base *next_lock, |
|
struct rt_mutex_waiter *orig_waiter, |
|
struct task_struct *top_task) |
|
{ |
|
struct rt_mutex_waiter *waiter, *top_waiter = orig_waiter; |
|
struct rt_mutex_waiter *prerequeue_top_waiter; |
|
int ret = 0, depth = 0; |
|
struct rt_mutex_base *lock; |
|
bool detect_deadlock; |
|
bool requeue = true; |
|
|
|
detect_deadlock = rt_mutex_cond_detect_deadlock(orig_waiter, chwalk); |
|
|
|
/* |
|
* The (de)boosting is a step by step approach with a lot of |
|
* pitfalls. We want this to be preemptible and we want hold a |
|
* maximum of two locks per step. So we have to check |
|
* carefully whether things change under us. |
|
*/ |
|
again: |
|
/* |
|
* We limit the lock chain length for each invocation. |
|
*/ |
|
if (++depth > max_lock_depth) { |
|
static int prev_max; |
|
|
|
/* |
|
* Print this only once. If the admin changes the limit, |
|
* print a new message when reaching the limit again. |
|
*/ |
|
if (prev_max != max_lock_depth) { |
|
prev_max = max_lock_depth; |
|
printk(KERN_WARNING "Maximum lock depth %d reached " |
|
"task: %s (%d)\n", max_lock_depth, |
|
top_task->comm, task_pid_nr(top_task)); |
|
} |
|
put_task_struct(task); |
|
|
|
return -EDEADLK; |
|
} |
|
|
|
/* |
|
* We are fully preemptible here and only hold the refcount on |
|
* @task. So everything can have changed under us since the |
|
* caller or our own code below (goto retry/again) dropped all |
|
* locks. |
|
*/ |
|
retry: |
|
/* |
|
* [1] Task cannot go away as we did a get_task() before ! |
|
*/ |
|
raw_spin_lock_irq(&task->pi_lock); |
|
|
|
/* |
|
* [2] Get the waiter on which @task is blocked on. |
|
*/ |
|
waiter = task->pi_blocked_on; |
|
|
|
/* |
|
* [3] check_exit_conditions_1() protected by task->pi_lock. |
|
*/ |
|
|
|
/* |
|
* Check whether the end of the boosting chain has been |
|
* reached or the state of the chain has changed while we |
|
* dropped the locks. |
|
*/ |
|
if (!waiter) |
|
goto out_unlock_pi; |
|
|
|
/* |
|
* Check the orig_waiter state. After we dropped the locks, |
|
* the previous owner of the lock might have released the lock. |
|
*/ |
|
if (orig_waiter && !rt_mutex_owner(orig_lock)) |
|
goto out_unlock_pi; |
|
|
|
/* |
|
* We dropped all locks after taking a refcount on @task, so |
|
* the task might have moved on in the lock chain or even left |
|
* the chain completely and blocks now on an unrelated lock or |
|
* on @orig_lock. |
|
* |
|
* We stored the lock on which @task was blocked in @next_lock, |
|
* so we can detect the chain change. |
|
*/ |
|
if (next_lock != waiter->lock) |
|
goto out_unlock_pi; |
|
|
|
/* |
|
* There could be 'spurious' loops in the lock graph due to ww_mutex, |
|
* consider: |
|
* |
|
* P1: A, ww_A, ww_B |
|
* P2: ww_B, ww_A |
|
* P3: A |
|
* |
|
* P3 should not return -EDEADLK because it gets trapped in the cycle |
|
* created by P1 and P2 (which will resolve -- and runs into |
|
* max_lock_depth above). Therefore disable detect_deadlock such that |
|
* the below termination condition can trigger once all relevant tasks |
|
* are boosted. |
|
* |
|
* Even when we start with ww_mutex we can disable deadlock detection, |
|
* since we would supress a ww_mutex induced deadlock at [6] anyway. |
|
* Supressing it here however is not sufficient since we might still |
|
* hit [6] due to adjustment driven iteration. |
|
* |
|
* NOTE: if someone were to create a deadlock between 2 ww_classes we'd |
|
* utterly fail to report it; lockdep should. |
|
*/ |
|
if (IS_ENABLED(CONFIG_PREEMPT_RT) && waiter->ww_ctx && detect_deadlock) |
|
detect_deadlock = false; |
|
|
|
/* |
|
* Drop out, when the task has no waiters. Note, |
|
* top_waiter can be NULL, when we are in the deboosting |
|
* mode! |
|
*/ |
|
if (top_waiter) { |
|
if (!task_has_pi_waiters(task)) |
|
goto out_unlock_pi; |
|
/* |
|
* If deadlock detection is off, we stop here if we |
|
* are not the top pi waiter of the task. If deadlock |
|
* detection is enabled we continue, but stop the |
|
* requeueing in the chain walk. |
|
*/ |
|
if (top_waiter != task_top_pi_waiter(task)) { |
|
if (!detect_deadlock) |
|
goto out_unlock_pi; |
|
else |
|
requeue = false; |
|
} |
|
} |
|
|
|
/* |
|
* If the waiter priority is the same as the task priority |
|
* then there is no further priority adjustment necessary. If |
|
* deadlock detection is off, we stop the chain walk. If its |
|
* enabled we continue, but stop the requeueing in the chain |
|
* walk. |
|
*/ |
|
if (rt_mutex_waiter_equal(waiter, task_to_waiter(task))) { |
|
if (!detect_deadlock) |
|
goto out_unlock_pi; |
|
else |
|
requeue = false; |
|
} |
|
|
|
/* |
|
* [4] Get the next lock |
|
*/ |
|
lock = waiter->lock; |
|
/* |
|
* [5] We need to trylock here as we are holding task->pi_lock, |
|
* which is the reverse lock order versus the other rtmutex |
|
* operations. |
|
*/ |
|
if (!raw_spin_trylock(&lock->wait_lock)) { |
|
raw_spin_unlock_irq(&task->pi_lock); |
|
cpu_relax(); |
|
goto retry; |
|
} |
|
|
|
/* |
|
* [6] check_exit_conditions_2() protected by task->pi_lock and |
|
* lock->wait_lock. |
|
* |
|
* Deadlock detection. If the lock is the same as the original |
|
* lock which caused us to walk the lock chain or if the |
|
* current lock is owned by the task which initiated the chain |
|
* walk, we detected a deadlock. |
|
*/ |
|
if (lock == orig_lock || rt_mutex_owner(lock) == top_task) { |
|
ret = -EDEADLK; |
|
|
|
/* |
|
* When the deadlock is due to ww_mutex; also see above. Don't |
|
* report the deadlock and instead let the ww_mutex wound/die |
|
* logic pick which of the contending threads gets -EDEADLK. |
|
* |
|
* NOTE: assumes the cycle only contains a single ww_class; any |
|
* other configuration and we fail to report; also, see |
|
* lockdep. |
|
*/ |
|
if (IS_ENABLED(CONFIG_PREEMPT_RT) && orig_waiter && orig_waiter->ww_ctx) |
|
ret = 0; |
|
|
|
raw_spin_unlock(&lock->wait_lock); |
|
goto out_unlock_pi; |
|
} |
|
|
|
/* |
|
* If we just follow the lock chain for deadlock detection, no |
|
* need to do all the requeue operations. To avoid a truckload |
|
* of conditionals around the various places below, just do the |
|
* minimum chain walk checks. |
|
*/ |
|
if (!requeue) { |
|
/* |
|
* No requeue[7] here. Just release @task [8] |
|
*/ |
|
raw_spin_unlock(&task->pi_lock); |
|
put_task_struct(task); |
|
|
|
/* |
|
* [9] check_exit_conditions_3 protected by lock->wait_lock. |
|
* If there is no owner of the lock, end of chain. |
|
*/ |
|
if (!rt_mutex_owner(lock)) { |
|
raw_spin_unlock_irq(&lock->wait_lock); |
|
return 0; |
|
} |
|
|
|
/* [10] Grab the next task, i.e. owner of @lock */ |
|
task = get_task_struct(rt_mutex_owner(lock)); |
|
raw_spin_lock(&task->pi_lock); |
|
|
|
/* |
|
* No requeue [11] here. We just do deadlock detection. |
|
* |
|
* [12] Store whether owner is blocked |
|
* itself. Decision is made after dropping the locks |
|
*/ |
|
next_lock = task_blocked_on_lock(task); |
|
/* |
|
* Get the top waiter for the next iteration |
|
*/ |
|
top_waiter = rt_mutex_top_waiter(lock); |
|
|
|
/* [13] Drop locks */ |
|
raw_spin_unlock(&task->pi_lock); |
|
raw_spin_unlock_irq(&lock->wait_lock); |
|
|
|
/* If owner is not blocked, end of chain. */ |
|
if (!next_lock) |
|
goto out_put_task; |
|
goto again; |
|
} |
|
|
|
/* |
|
* Store the current top waiter before doing the requeue |
|
* operation on @lock. We need it for the boost/deboost |
|
* decision below. |
|
*/ |
|
prerequeue_top_waiter = rt_mutex_top_waiter(lock); |
|
|
|
/* [7] Requeue the waiter in the lock waiter tree. */ |
|
rt_mutex_dequeue(lock, waiter); |
|
|
|
/* |
|
* Update the waiter prio fields now that we're dequeued. |
|
* |
|
* These values can have changed through either: |
|
* |
|
* sys_sched_set_scheduler() / sys_sched_setattr() |
|
* |
|
* or |
|
* |
|
* DL CBS enforcement advancing the effective deadline. |
|
* |
|
* Even though pi_waiters also uses these fields, and that tree is only |
|
* updated in [11], we can do this here, since we hold [L], which |
|
* serializes all pi_waiters access and rb_erase() does not care about |
|
* the values of the node being removed. |
|
*/ |
|
waiter_update_prio(waiter, task); |
|
|
|
rt_mutex_enqueue(lock, waiter); |
|
|
|
/* [8] Release the task */ |
|
raw_spin_unlock(&task->pi_lock); |
|
put_task_struct(task); |
|
|
|
/* |
|
* [9] check_exit_conditions_3 protected by lock->wait_lock. |
|
* |
|
* We must abort the chain walk if there is no lock owner even |
|
* in the dead lock detection case, as we have nothing to |
|
* follow here. This is the end of the chain we are walking. |
|
*/ |
|
if (!rt_mutex_owner(lock)) { |
|
/* |
|
* If the requeue [7] above changed the top waiter, |
|
* then we need to wake the new top waiter up to try |
|
* to get the lock. |
|
*/ |
|
if (prerequeue_top_waiter != rt_mutex_top_waiter(lock)) |
|
wake_up_state(waiter->task, waiter->wake_state); |
|
raw_spin_unlock_irq(&lock->wait_lock); |
|
return 0; |
|
} |
|
|
|
/* [10] Grab the next task, i.e. the owner of @lock */ |
|
task = get_task_struct(rt_mutex_owner(lock)); |
|
raw_spin_lock(&task->pi_lock); |
|
|
|
/* [11] requeue the pi waiters if necessary */ |
|
if (waiter == rt_mutex_top_waiter(lock)) { |
|
/* |
|
* The waiter became the new top (highest priority) |
|
* waiter on the lock. Replace the previous top waiter |
|
* in the owner tasks pi waiters tree with this waiter |
|
* and adjust the priority of the owner. |
|
*/ |
|
rt_mutex_dequeue_pi(task, prerequeue_top_waiter); |
|
rt_mutex_enqueue_pi(task, waiter); |
|
rt_mutex_adjust_prio(task); |
|
|
|
} else if (prerequeue_top_waiter == waiter) { |
|
/* |
|
* The waiter was the top waiter on the lock, but is |
|
* no longer the top priority waiter. Replace waiter in |
|
* the owner tasks pi waiters tree with the new top |
|
* (highest priority) waiter and adjust the priority |
|
* of the owner. |
|
* The new top waiter is stored in @waiter so that |
|
* @waiter == @top_waiter evaluates to true below and |
|
* we continue to deboost the rest of the chain. |
|
*/ |
|
rt_mutex_dequeue_pi(task, waiter); |
|
waiter = rt_mutex_top_waiter(lock); |
|
rt_mutex_enqueue_pi(task, waiter); |
|
rt_mutex_adjust_prio(task); |
|
} else { |
|
/* |
|
* Nothing changed. No need to do any priority |
|
* adjustment. |
|
*/ |
|
} |
|
|
|
/* |
|
* [12] check_exit_conditions_4() protected by task->pi_lock |
|
* and lock->wait_lock. The actual decisions are made after we |
|
* dropped the locks. |
|
* |
|
* Check whether the task which owns the current lock is pi |
|
* blocked itself. If yes we store a pointer to the lock for |
|
* the lock chain change detection above. After we dropped |
|
* task->pi_lock next_lock cannot be dereferenced anymore. |
|
*/ |
|
next_lock = task_blocked_on_lock(task); |
|
/* |
|
* Store the top waiter of @lock for the end of chain walk |
|
* decision below. |
|
*/ |
|
top_waiter = rt_mutex_top_waiter(lock); |
|
|
|
/* [13] Drop the locks */ |
|
raw_spin_unlock(&task->pi_lock); |
|
raw_spin_unlock_irq(&lock->wait_lock); |
|
|
|
/* |
|
* Make the actual exit decisions [12], based on the stored |
|
* values. |
|
* |
|
* We reached the end of the lock chain. Stop right here. No |
|
* point to go back just to figure that out. |
|
*/ |
|
if (!next_lock) |
|
goto out_put_task; |
|
|
|
/* |
|
* If the current waiter is not the top waiter on the lock, |
|
* then we can stop the chain walk here if we are not in full |
|
* deadlock detection mode. |
|
*/ |
|
if (!detect_deadlock && waiter != top_waiter) |
|
goto out_put_task; |
|
|
|
goto again; |
|
|
|
out_unlock_pi: |
|
raw_spin_unlock_irq(&task->pi_lock); |
|
out_put_task: |
|
put_task_struct(task); |
|
|
|
return ret; |
|
} |
|
|
|
/* |
|
* Try to take an rt-mutex |
|
* |
|
* Must be called with lock->wait_lock held and interrupts disabled |
|
* |
|
* @lock: The lock to be acquired. |
|
* @task: The task which wants to acquire the lock |
|
* @waiter: The waiter that is queued to the lock's wait tree if the |
|
* callsite called task_blocked_on_lock(), otherwise NULL |
|
*/ |
|
static int __sched |
|
try_to_take_rt_mutex(struct rt_mutex_base *lock, struct task_struct *task, |
|
struct rt_mutex_waiter *waiter) |
|
{ |
|
lockdep_assert_held(&lock->wait_lock); |
|
|
|
/* |
|
* Before testing whether we can acquire @lock, we set the |
|
* RT_MUTEX_HAS_WAITERS bit in @lock->owner. This forces all |
|
* other tasks which try to modify @lock into the slow path |
|
* and they serialize on @lock->wait_lock. |
|
* |
|
* The RT_MUTEX_HAS_WAITERS bit can have a transitional state |
|
* as explained at the top of this file if and only if: |
|
* |
|
* - There is a lock owner. The caller must fixup the |
|
* transient state if it does a trylock or leaves the lock |
|
* function due to a signal or timeout. |
|
* |
|
* - @task acquires the lock and there are no other |
|
* waiters. This is undone in rt_mutex_set_owner(@task) at |
|
* the end of this function. |
|
*/ |
|
mark_rt_mutex_waiters(lock); |
|
|
|
/* |
|
* If @lock has an owner, give up. |
|
*/ |
|
if (rt_mutex_owner(lock)) |
|
return 0; |
|
|
|
/* |
|
* If @waiter != NULL, @task has already enqueued the waiter |
|
* into @lock waiter tree. If @waiter == NULL then this is a |
|
* trylock attempt. |
|
*/ |
|
if (waiter) { |
|
struct rt_mutex_waiter *top_waiter = rt_mutex_top_waiter(lock); |
|
|
|
/* |
|
* If waiter is the highest priority waiter of @lock, |
|
* or allowed to steal it, take it over. |
|
*/ |
|
if (waiter == top_waiter || rt_mutex_steal(waiter, top_waiter)) { |
|
/* |
|
* We can acquire the lock. Remove the waiter from the |
|
* lock waiters tree. |
|
*/ |
|
rt_mutex_dequeue(lock, waiter); |
|
} else { |
|
return 0; |
|
} |
|
} else { |
|
/* |
|
* If the lock has waiters already we check whether @task is |
|
* eligible to take over the lock. |
|
* |
|
* If there are no other waiters, @task can acquire |
|
* the lock. @task->pi_blocked_on is NULL, so it does |
|
* not need to be dequeued. |
|
*/ |
|
if (rt_mutex_has_waiters(lock)) { |
|
/* Check whether the trylock can steal it. */ |
|
if (!rt_mutex_steal(task_to_waiter(task), |
|
rt_mutex_top_waiter(lock))) |
|
return 0; |
|
|
|
/* |
|
* The current top waiter stays enqueued. We |
|
* don't have to change anything in the lock |
|
* waiters order. |
|
*/ |
|
} else { |
|
/* |
|
* No waiters. Take the lock without the |
|
* pi_lock dance.@task->pi_blocked_on is NULL |
|
* and we have no waiters to enqueue in @task |
|
* pi waiters tree. |
|
*/ |
|
goto takeit; |
|
} |
|
} |
|
|
|
/* |
|
* Clear @task->pi_blocked_on. Requires protection by |
|
* @task->pi_lock. Redundant operation for the @waiter == NULL |
|
* case, but conditionals are more expensive than a redundant |
|
* store. |
|
*/ |
|
raw_spin_lock(&task->pi_lock); |
|
task->pi_blocked_on = NULL; |
|
/* |
|
* Finish the lock acquisition. @task is the new owner. If |
|
* other waiters exist we have to insert the highest priority |
|
* waiter into @task->pi_waiters tree. |
|
*/ |
|
if (rt_mutex_has_waiters(lock)) |
|
rt_mutex_enqueue_pi(task, rt_mutex_top_waiter(lock)); |
|
raw_spin_unlock(&task->pi_lock); |
|
|
|
takeit: |
|
/* |
|
* This either preserves the RT_MUTEX_HAS_WAITERS bit if there |
|
* are still waiters or clears it. |
|
*/ |
|
rt_mutex_set_owner(lock, task); |
|
|
|
return 1; |
|
} |
|
|
|
/* |
|
* Task blocks on lock. |
|
* |
|
* Prepare waiter and propagate pi chain |
|
* |
|
* This must be called with lock->wait_lock held and interrupts disabled |
|
*/ |
|
static int __sched task_blocks_on_rt_mutex(struct rt_mutex_base *lock, |
|
struct rt_mutex_waiter *waiter, |
|
struct task_struct *task, |
|
struct ww_acquire_ctx *ww_ctx, |
|
enum rtmutex_chainwalk chwalk) |
|
{ |
|
struct task_struct *owner = rt_mutex_owner(lock); |
|
struct rt_mutex_waiter *top_waiter = waiter; |
|
struct rt_mutex_base *next_lock; |
|
int chain_walk = 0, res; |
|
|
|
lockdep_assert_held(&lock->wait_lock); |
|
|
|
/* |
|
* Early deadlock detection. We really don't want the task to |
|
* enqueue on itself just to untangle the mess later. It's not |
|
* only an optimization. We drop the locks, so another waiter |
|
* can come in before the chain walk detects the deadlock. So |
|
* the other will detect the deadlock and return -EDEADLOCK, |
|
* which is wrong, as the other waiter is not in a deadlock |
|
* situation. |
|
* |
|
* Except for ww_mutex, in that case the chain walk must already deal |
|
* with spurious cycles, see the comments at [3] and [6]. |
|
*/ |
|
if (owner == task && !(build_ww_mutex() && ww_ctx)) |
|
return -EDEADLK; |
|
|
|
raw_spin_lock(&task->pi_lock); |
|
waiter->task = task; |
|
waiter->lock = lock; |
|
waiter_update_prio(waiter, task); |
|
|
|
/* Get the top priority waiter on the lock */ |
|
if (rt_mutex_has_waiters(lock)) |
|
top_waiter = rt_mutex_top_waiter(lock); |
|
rt_mutex_enqueue(lock, waiter); |
|
|
|
task->pi_blocked_on = waiter; |
|
|
|
raw_spin_unlock(&task->pi_lock); |
|
|
|
if (build_ww_mutex() && ww_ctx) { |
|
struct rt_mutex *rtm; |
|
|
|
/* Check whether the waiter should back out immediately */ |
|
rtm = container_of(lock, struct rt_mutex, rtmutex); |
|
res = __ww_mutex_add_waiter(waiter, rtm, ww_ctx); |
|
if (res) { |
|
raw_spin_lock(&task->pi_lock); |
|
rt_mutex_dequeue(lock, waiter); |
|
task->pi_blocked_on = NULL; |
|
raw_spin_unlock(&task->pi_lock); |
|
return res; |
|
} |
|
} |
|
|
|
if (!owner) |
|
return 0; |
|
|
|
raw_spin_lock(&owner->pi_lock); |
|
if (waiter == rt_mutex_top_waiter(lock)) { |
|
rt_mutex_dequeue_pi(owner, top_waiter); |
|
rt_mutex_enqueue_pi(owner, waiter); |
|
|
|
rt_mutex_adjust_prio(owner); |
|
if (owner->pi_blocked_on) |
|
chain_walk = 1; |
|
} else if (rt_mutex_cond_detect_deadlock(waiter, chwalk)) { |
|
chain_walk = 1; |
|
} |
|
|
|
/* Store the lock on which owner is blocked or NULL */ |
|
next_lock = task_blocked_on_lock(owner); |
|
|
|
raw_spin_unlock(&owner->pi_lock); |
|
/* |
|
* Even if full deadlock detection is on, if the owner is not |
|
* blocked itself, we can avoid finding this out in the chain |
|
* walk. |
|
*/ |
|
if (!chain_walk || !next_lock) |
|
return 0; |
|
|
|
/* |
|
* The owner can't disappear while holding a lock, |
|
* so the owner struct is protected by wait_lock. |
|
* Gets dropped in rt_mutex_adjust_prio_chain()! |
|
*/ |
|
get_task_struct(owner); |
|
|
|
raw_spin_unlock_irq(&lock->wait_lock); |
|
|
|
res = rt_mutex_adjust_prio_chain(owner, chwalk, lock, |
|
next_lock, waiter, task); |
|
|
|
raw_spin_lock_irq(&lock->wait_lock); |
|
|
|
return res; |
|
} |
|
|
|
/* |
|
* Remove the top waiter from the current tasks pi waiter tree and |
|
* queue it up. |
|
* |
|
* Called with lock->wait_lock held and interrupts disabled. |
|
*/ |
|
static void __sched mark_wakeup_next_waiter(struct rt_wake_q_head *wqh, |
|
struct rt_mutex_base *lock) |
|
{ |
|
struct rt_mutex_waiter *waiter; |
|
|
|
raw_spin_lock(¤t->pi_lock); |
|
|
|
waiter = rt_mutex_top_waiter(lock); |
|
|
|
/* |
|
* Remove it from current->pi_waiters and deboost. |
|
* |
|
* We must in fact deboost here in order to ensure we call |
|
* rt_mutex_setprio() to update p->pi_top_task before the |
|
* task unblocks. |
|
*/ |
|
rt_mutex_dequeue_pi(current, waiter); |
|
rt_mutex_adjust_prio(current); |
|
|
|
/* |
|
* As we are waking up the top waiter, and the waiter stays |
|
* queued on the lock until it gets the lock, this lock |
|
* obviously has waiters. Just set the bit here and this has |
|
* the added benefit of forcing all new tasks into the |
|
* slow path making sure no task of lower priority than |
|
* the top waiter can steal this lock. |
|
*/ |
|
lock->owner = (void *) RT_MUTEX_HAS_WAITERS; |
|
|
|
/* |
|
* We deboosted before waking the top waiter task such that we don't |
|
* run two tasks with the 'same' priority (and ensure the |
|
* p->pi_top_task pointer points to a blocked task). This however can |
|
* lead to priority inversion if we would get preempted after the |
|
* deboost but before waking our donor task, hence the preempt_disable() |
|
* before unlock. |
|
* |
|
* Pairs with preempt_enable() in rt_mutex_wake_up_q(); |
|
*/ |
|
preempt_disable(); |
|
rt_mutex_wake_q_add(wqh, waiter); |
|
raw_spin_unlock(¤t->pi_lock); |
|
} |
|
|
|
static int __sched __rt_mutex_slowtrylock(struct rt_mutex_base *lock) |
|
{ |
|
int ret = try_to_take_rt_mutex(lock, current, NULL); |
|
|
|
/* |
|
* try_to_take_rt_mutex() sets the lock waiters bit |
|
* unconditionally. Clean this up. |
|
*/ |
|
fixup_rt_mutex_waiters(lock); |
|
|
|
return ret; |
|
} |
|
|
|
/* |
|
* Slow path try-lock function: |
|
*/ |
|
static int __sched rt_mutex_slowtrylock(struct rt_mutex_base *lock) |
|
{ |
|
unsigned long flags; |
|
int ret; |
|
|
|
/* |
|
* If the lock already has an owner we fail to get the lock. |
|
* This can be done without taking the @lock->wait_lock as |
|
* it is only being read, and this is a trylock anyway. |
|
*/ |
|
if (rt_mutex_owner(lock)) |
|
return 0; |
|
|
|
/* |
|
* The mutex has currently no owner. Lock the wait lock and try to |
|
* acquire the lock. We use irqsave here to support early boot calls. |
|
*/ |
|
raw_spin_lock_irqsave(&lock->wait_lock, flags); |
|
|
|
ret = __rt_mutex_slowtrylock(lock); |
|
|
|
raw_spin_unlock_irqrestore(&lock->wait_lock, flags); |
|
|
|
return ret; |
|
} |
|
|
|
static __always_inline int __rt_mutex_trylock(struct rt_mutex_base *lock) |
|
{ |
|
if (likely(rt_mutex_cmpxchg_acquire(lock, NULL, current))) |
|
return 1; |
|
|
|
return rt_mutex_slowtrylock(lock); |
|
} |
|
|
|
/* |
|
* Slow path to release a rt-mutex. |
|
*/ |
|
static void __sched rt_mutex_slowunlock(struct rt_mutex_base *lock) |
|
{ |
|
DEFINE_RT_WAKE_Q(wqh); |
|
unsigned long flags; |
|
|
|
/* irqsave required to support early boot calls */ |
|
raw_spin_lock_irqsave(&lock->wait_lock, flags); |
|
|
|
debug_rt_mutex_unlock(lock); |
|
|
|
/* |
|
* We must be careful here if the fast path is enabled. If we |
|
* have no waiters queued we cannot set owner to NULL here |
|
* because of: |
|
* |
|
* foo->lock->owner = NULL; |
|
* rtmutex_lock(foo->lock); <- fast path |
|
* free = atomic_dec_and_test(foo->refcnt); |
|
* rtmutex_unlock(foo->lock); <- fast path |
|
* if (free) |
|
* kfree(foo); |
|
* raw_spin_unlock(foo->lock->wait_lock); |
|
* |
|
* So for the fastpath enabled kernel: |
|
* |
|
* Nothing can set the waiters bit as long as we hold |
|
* lock->wait_lock. So we do the following sequence: |
|
* |
|
* owner = rt_mutex_owner(lock); |
|
* clear_rt_mutex_waiters(lock); |
|
* raw_spin_unlock(&lock->wait_lock); |
|
* if (cmpxchg(&lock->owner, owner, 0) == owner) |
|
* return; |
|
* goto retry; |
|
* |
|
* The fastpath disabled variant is simple as all access to |
|
* lock->owner is serialized by lock->wait_lock: |
|
* |
|
* lock->owner = NULL; |
|
* raw_spin_unlock(&lock->wait_lock); |
|
*/ |
|
while (!rt_mutex_has_waiters(lock)) { |
|
/* Drops lock->wait_lock ! */ |
|
if (unlock_rt_mutex_safe(lock, flags) == true) |
|
return; |
|
/* Relock the rtmutex and try again */ |
|
raw_spin_lock_irqsave(&lock->wait_lock, flags); |
|
} |
|
|
|
/* |
|
* The wakeup next waiter path does not suffer from the above |
|
* race. See the comments there. |
|
* |
|
* Queue the next waiter for wakeup once we release the wait_lock. |
|
*/ |
|
mark_wakeup_next_waiter(&wqh, lock); |
|
raw_spin_unlock_irqrestore(&lock->wait_lock, flags); |
|
|
|
rt_mutex_wake_up_q(&wqh); |
|
} |
|
|
|
static __always_inline void __rt_mutex_unlock(struct rt_mutex_base *lock) |
|
{ |
|
if (likely(rt_mutex_cmpxchg_release(lock, current, NULL))) |
|
return; |
|
|
|
rt_mutex_slowunlock(lock); |
|
} |
|
|
|
#ifdef CONFIG_SMP |
|
static bool rtmutex_spin_on_owner(struct rt_mutex_base *lock, |
|
struct rt_mutex_waiter *waiter, |
|
struct task_struct *owner) |
|
{ |
|
bool res = true; |
|
|
|
rcu_read_lock(); |
|
for (;;) { |
|
/* If owner changed, trylock again. */ |
|
if (owner != rt_mutex_owner(lock)) |
|
break; |
|
/* |
|
* Ensure that @owner is dereferenced after checking that |
|
* the lock owner still matches @owner. If that fails, |
|
* @owner might point to freed memory. If it still matches, |
|
* the rcu_read_lock() ensures the memory stays valid. |
|
*/ |
|
barrier(); |
|
/* |
|
* Stop spinning when: |
|
* - the lock owner has been scheduled out |
|
* - current is not longer the top waiter |
|
* - current is requested to reschedule (redundant |
|
* for CONFIG_PREEMPT_RCU=y) |
|
* - the VCPU on which owner runs is preempted |
|
*/ |
|
if (!owner_on_cpu(owner) || need_resched() || |
|
!rt_mutex_waiter_is_top_waiter(lock, waiter)) { |
|
res = false; |
|
break; |
|
} |
|
cpu_relax(); |
|
} |
|
rcu_read_unlock(); |
|
return res; |
|
} |
|
#else |
|
static bool rtmutex_spin_on_owner(struct rt_mutex_base *lock, |
|
struct rt_mutex_waiter *waiter, |
|
struct task_struct *owner) |
|
{ |
|
return false; |
|
} |
|
#endif |
|
|
|
#ifdef RT_MUTEX_BUILD_MUTEX |
|
/* |
|
* Functions required for: |
|
* - rtmutex, futex on all kernels |
|
* - mutex and rwsem substitutions on RT kernels |
|
*/ |
|
|
|
/* |
|
* Remove a waiter from a lock and give up |
|
* |
|
* Must be called with lock->wait_lock held and interrupts disabled. It must |
|
* have just failed to try_to_take_rt_mutex(). |
|
*/ |
|
static void __sched remove_waiter(struct rt_mutex_base *lock, |
|
struct rt_mutex_waiter *waiter) |
|
{ |
|
bool is_top_waiter = (waiter == rt_mutex_top_waiter(lock)); |
|
struct task_struct *owner = rt_mutex_owner(lock); |
|
struct rt_mutex_base *next_lock; |
|
|
|
lockdep_assert_held(&lock->wait_lock); |
|
|
|
raw_spin_lock(¤t->pi_lock); |
|
rt_mutex_dequeue(lock, waiter); |
|
current->pi_blocked_on = NULL; |
|
raw_spin_unlock(¤t->pi_lock); |
|
|
|
/* |
|
* Only update priority if the waiter was the highest priority |
|
* waiter of the lock and there is an owner to update. |
|
*/ |
|
if (!owner || !is_top_waiter) |
|
return; |
|
|
|
raw_spin_lock(&owner->pi_lock); |
|
|
|
rt_mutex_dequeue_pi(owner, waiter); |
|
|
|
if (rt_mutex_has_waiters(lock)) |
|
rt_mutex_enqueue_pi(owner, rt_mutex_top_waiter(lock)); |
|
|
|
rt_mutex_adjust_prio(owner); |
|
|
|
/* Store the lock on which owner is blocked or NULL */ |
|
next_lock = task_blocked_on_lock(owner); |
|
|
|
raw_spin_unlock(&owner->pi_lock); |
|
|
|
/* |
|
* Don't walk the chain, if the owner task is not blocked |
|
* itself. |
|
*/ |
|
if (!next_lock) |
|
return; |
|
|
|
/* gets dropped in rt_mutex_adjust_prio_chain()! */ |
|
get_task_struct(owner); |
|
|
|
raw_spin_unlock_irq(&lock->wait_lock); |
|
|
|
rt_mutex_adjust_prio_chain(owner, RT_MUTEX_MIN_CHAINWALK, lock, |
|
next_lock, NULL, current); |
|
|
|
raw_spin_lock_irq(&lock->wait_lock); |
|
} |
|
|
|
/** |
|
* rt_mutex_slowlock_block() - Perform the wait-wake-try-to-take loop |
|
* @lock: the rt_mutex to take |
|
* @ww_ctx: WW mutex context pointer |
|
* @state: the state the task should block in (TASK_INTERRUPTIBLE |
|
* or TASK_UNINTERRUPTIBLE) |
|
* @timeout: the pre-initialized and started timer, or NULL for none |
|
* @waiter: the pre-initialized rt_mutex_waiter |
|
* |
|
* Must be called with lock->wait_lock held and interrupts disabled |
|
*/ |
|
static int __sched rt_mutex_slowlock_block(struct rt_mutex_base *lock, |
|
struct ww_acquire_ctx *ww_ctx, |
|
unsigned int state, |
|
struct hrtimer_sleeper *timeout, |
|
struct rt_mutex_waiter *waiter) |
|
{ |
|
struct rt_mutex *rtm = container_of(lock, struct rt_mutex, rtmutex); |
|
struct task_struct *owner; |
|
int ret = 0; |
|
|
|
for (;;) { |
|
/* Try to acquire the lock: */ |
|
if (try_to_take_rt_mutex(lock, current, waiter)) |
|
break; |
|
|
|
if (timeout && !timeout->task) { |
|
ret = -ETIMEDOUT; |
|
break; |
|
} |
|
if (signal_pending_state(state, current)) { |
|
ret = -EINTR; |
|
break; |
|
} |
|
|
|
if (build_ww_mutex() && ww_ctx) { |
|
ret = __ww_mutex_check_kill(rtm, waiter, ww_ctx); |
|
if (ret) |
|
break; |
|
} |
|
|
|
if (waiter == rt_mutex_top_waiter(lock)) |
|
owner = rt_mutex_owner(lock); |
|
else |
|
owner = NULL; |
|
raw_spin_unlock_irq(&lock->wait_lock); |
|
|
|
if (!owner || !rtmutex_spin_on_owner(lock, waiter, owner)) |
|
schedule(); |
|
|
|
raw_spin_lock_irq(&lock->wait_lock); |
|
set_current_state(state); |
|
} |
|
|
|
__set_current_state(TASK_RUNNING); |
|
return ret; |
|
} |
|
|
|
static void __sched rt_mutex_handle_deadlock(int res, int detect_deadlock, |
|
struct rt_mutex_waiter *w) |
|
{ |
|
/* |
|
* If the result is not -EDEADLOCK or the caller requested |
|
* deadlock detection, nothing to do here. |
|
*/ |
|
if (res != -EDEADLOCK || detect_deadlock) |
|
return; |
|
|
|
if (build_ww_mutex() && w->ww_ctx) |
|
return; |
|
|
|
/* |
|
* Yell loudly and stop the task right here. |
|
*/ |
|
WARN(1, "rtmutex deadlock detected\n"); |
|
while (1) { |
|
set_current_state(TASK_INTERRUPTIBLE); |
|
schedule(); |
|
} |
|
} |
|
|
|
/** |
|
* __rt_mutex_slowlock - Locking slowpath invoked with lock::wait_lock held |
|
* @lock: The rtmutex to block lock |
|
* @ww_ctx: WW mutex context pointer |
|
* @state: The task state for sleeping |
|
* @chwalk: Indicator whether full or partial chainwalk is requested |
|
* @waiter: Initializer waiter for blocking |
|
*/ |
|
static int __sched __rt_mutex_slowlock(struct rt_mutex_base *lock, |
|
struct ww_acquire_ctx *ww_ctx, |
|
unsigned int state, |
|
enum rtmutex_chainwalk chwalk, |
|
struct rt_mutex_waiter *waiter) |
|
{ |
|
struct rt_mutex *rtm = container_of(lock, struct rt_mutex, rtmutex); |
|
struct ww_mutex *ww = ww_container_of(rtm); |
|
int ret; |
|
|
|
lockdep_assert_held(&lock->wait_lock); |
|
|
|
/* Try to acquire the lock again: */ |
|
if (try_to_take_rt_mutex(lock, current, NULL)) { |
|
if (build_ww_mutex() && ww_ctx) { |
|
__ww_mutex_check_waiters(rtm, ww_ctx); |
|
ww_mutex_lock_acquired(ww, ww_ctx); |
|
} |
|
return 0; |
|
} |
|
|
|
set_current_state(state); |
|
|
|
trace_contention_begin(lock, LCB_F_RT); |
|
|
|
ret = task_blocks_on_rt_mutex(lock, waiter, current, ww_ctx, chwalk); |
|
if (likely(!ret)) |
|
ret = rt_mutex_slowlock_block(lock, ww_ctx, state, NULL, waiter); |
|
|
|
if (likely(!ret)) { |
|
/* acquired the lock */ |
|
if (build_ww_mutex() && ww_ctx) { |
|
if (!ww_ctx->is_wait_die) |
|
__ww_mutex_check_waiters(rtm, ww_ctx); |
|
ww_mutex_lock_acquired(ww, ww_ctx); |
|
} |
|
} else { |
|
__set_current_state(TASK_RUNNING); |
|
remove_waiter(lock, waiter); |
|
rt_mutex_handle_deadlock(ret, chwalk, waiter); |
|
} |
|
|
|
/* |
|
* try_to_take_rt_mutex() sets the waiter bit |
|
* unconditionally. We might have to fix that up. |
|
*/ |
|
fixup_rt_mutex_waiters(lock); |
|
|
|
trace_contention_end(lock, ret); |
|
|
|
return ret; |
|
} |
|
|
|
static inline int __rt_mutex_slowlock_locked(struct rt_mutex_base *lock, |
|
struct ww_acquire_ctx *ww_ctx, |
|
unsigned int state) |
|
{ |
|
struct rt_mutex_waiter waiter; |
|
int ret; |
|
|
|
rt_mutex_init_waiter(&waiter); |
|
waiter.ww_ctx = ww_ctx; |
|
|
|
ret = __rt_mutex_slowlock(lock, ww_ctx, state, RT_MUTEX_MIN_CHAINWALK, |
|
&waiter); |
|
|
|
debug_rt_mutex_free_waiter(&waiter); |
|
return ret; |
|
} |
|
|
|
/* |
|
* rt_mutex_slowlock - Locking slowpath invoked when fast path fails |
|
* @lock: The rtmutex to block lock |
|
* @ww_ctx: WW mutex context pointer |
|
* @state: The task state for sleeping |
|
*/ |
|
static int __sched rt_mutex_slowlock(struct rt_mutex_base *lock, |
|
struct ww_acquire_ctx *ww_ctx, |
|
unsigned int state) |
|
{ |
|
unsigned long flags; |
|
int ret; |
|
|
|
/* |
|
* Technically we could use raw_spin_[un]lock_irq() here, but this can |
|
* be called in early boot if the cmpxchg() fast path is disabled |
|
* (debug, no architecture support). In this case we will acquire the |
|
* rtmutex with lock->wait_lock held. But we cannot unconditionally |
|
* enable interrupts in that early boot case. So we need to use the |
|
* irqsave/restore variants. |
|
*/ |
|
raw_spin_lock_irqsave(&lock->wait_lock, flags); |
|
ret = __rt_mutex_slowlock_locked(lock, ww_ctx, state); |
|
raw_spin_unlock_irqrestore(&lock->wait_lock, flags); |
|
|
|
return ret; |
|
} |
|
|
|
static __always_inline int __rt_mutex_lock(struct rt_mutex_base *lock, |
|
unsigned int state) |
|
{ |
|
if (likely(rt_mutex_cmpxchg_acquire(lock, NULL, current))) |
|
return 0; |
|
|
|
return rt_mutex_slowlock(lock, NULL, state); |
|
} |
|
#endif /* RT_MUTEX_BUILD_MUTEX */ |
|
|
|
#ifdef RT_MUTEX_BUILD_SPINLOCKS |
|
/* |
|
* Functions required for spin/rw_lock substitution on RT kernels |
|
*/ |
|
|
|
/** |
|
* rtlock_slowlock_locked - Slow path lock acquisition for RT locks |
|
* @lock: The underlying RT mutex |
|
*/ |
|
static void __sched rtlock_slowlock_locked(struct rt_mutex_base *lock) |
|
{ |
|
struct rt_mutex_waiter waiter; |
|
struct task_struct *owner; |
|
|
|
lockdep_assert_held(&lock->wait_lock); |
|
|
|
if (try_to_take_rt_mutex(lock, current, NULL)) |
|
return; |
|
|
|
rt_mutex_init_rtlock_waiter(&waiter); |
|
|
|
/* Save current state and set state to TASK_RTLOCK_WAIT */ |
|
current_save_and_set_rtlock_wait_state(); |
|
|
|
trace_contention_begin(lock, LCB_F_RT); |
|
|
|
task_blocks_on_rt_mutex(lock, &waiter, current, NULL, RT_MUTEX_MIN_CHAINWALK); |
|
|
|
for (;;) { |
|
/* Try to acquire the lock again */ |
|
if (try_to_take_rt_mutex(lock, current, &waiter)) |
|
break; |
|
|
|
if (&waiter == rt_mutex_top_waiter(lock)) |
|
owner = rt_mutex_owner(lock); |
|
else |
|
owner = NULL; |
|
raw_spin_unlock_irq(&lock->wait_lock); |
|
|
|
if (!owner || !rtmutex_spin_on_owner(lock, &waiter, owner)) |
|
schedule_rtlock(); |
|
|
|
raw_spin_lock_irq(&lock->wait_lock); |
|
set_current_state(TASK_RTLOCK_WAIT); |
|
} |
|
|
|
/* Restore the task state */ |
|
current_restore_rtlock_saved_state(); |
|
|
|
/* |
|
* try_to_take_rt_mutex() sets the waiter bit unconditionally. |
|
* We might have to fix that up: |
|
*/ |
|
fixup_rt_mutex_waiters(lock); |
|
debug_rt_mutex_free_waiter(&waiter); |
|
|
|
trace_contention_end(lock, 0); |
|
} |
|
|
|
static __always_inline void __sched rtlock_slowlock(struct rt_mutex_base *lock) |
|
{ |
|
unsigned long flags; |
|
|
|
raw_spin_lock_irqsave(&lock->wait_lock, flags); |
|
rtlock_slowlock_locked(lock); |
|
raw_spin_unlock_irqrestore(&lock->wait_lock, flags); |
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} |
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#endif /* RT_MUTEX_BUILD_SPINLOCKS */
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