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272 lines
7.5 KiB
272 lines
7.5 KiB
// SPDX-License-Identifier: GPL-2.0+ |
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/* |
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* Sleepable Read-Copy Update mechanism for mutual exclusion, |
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* tiny version for non-preemptible single-CPU use. |
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* |
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* Copyright (C) IBM Corporation, 2017 |
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* |
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* Author: Paul McKenney <[email protected]> |
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*/ |
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#include <linux/export.h> |
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#include <linux/mutex.h> |
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#include <linux/preempt.h> |
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#include <linux/rcupdate_wait.h> |
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#include <linux/sched.h> |
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#include <linux/delay.h> |
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#include <linux/srcu.h> |
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#include <linux/rcu_node_tree.h> |
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#include "rcu_segcblist.h" |
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#include "rcu.h" |
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int rcu_scheduler_active __read_mostly; |
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static LIST_HEAD(srcu_boot_list); |
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static bool srcu_init_done; |
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static int init_srcu_struct_fields(struct srcu_struct *ssp) |
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{ |
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ssp->srcu_lock_nesting[0] = 0; |
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ssp->srcu_lock_nesting[1] = 0; |
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init_swait_queue_head(&ssp->srcu_wq); |
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ssp->srcu_cb_head = NULL; |
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ssp->srcu_cb_tail = &ssp->srcu_cb_head; |
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ssp->srcu_gp_running = false; |
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ssp->srcu_gp_waiting = false; |
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ssp->srcu_idx = 0; |
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ssp->srcu_idx_max = 0; |
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INIT_WORK(&ssp->srcu_work, srcu_drive_gp); |
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INIT_LIST_HEAD(&ssp->srcu_work.entry); |
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return 0; |
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} |
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#ifdef CONFIG_DEBUG_LOCK_ALLOC |
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int __init_srcu_struct(struct srcu_struct *ssp, const char *name, |
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struct lock_class_key *key) |
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{ |
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/* Don't re-initialize a lock while it is held. */ |
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debug_check_no_locks_freed((void *)ssp, sizeof(*ssp)); |
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lockdep_init_map(&ssp->dep_map, name, key, 0); |
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return init_srcu_struct_fields(ssp); |
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} |
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EXPORT_SYMBOL_GPL(__init_srcu_struct); |
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#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ |
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/* |
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* init_srcu_struct - initialize a sleep-RCU structure |
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* @ssp: structure to initialize. |
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* |
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* Must invoke this on a given srcu_struct before passing that srcu_struct |
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* to any other function. Each srcu_struct represents a separate domain |
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* of SRCU protection. |
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*/ |
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int init_srcu_struct(struct srcu_struct *ssp) |
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{ |
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return init_srcu_struct_fields(ssp); |
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} |
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EXPORT_SYMBOL_GPL(init_srcu_struct); |
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#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */ |
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/* |
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* cleanup_srcu_struct - deconstruct a sleep-RCU structure |
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* @ssp: structure to clean up. |
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* |
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* Must invoke this after you are finished using a given srcu_struct that |
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* was initialized via init_srcu_struct(), else you leak memory. |
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*/ |
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void cleanup_srcu_struct(struct srcu_struct *ssp) |
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{ |
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WARN_ON(ssp->srcu_lock_nesting[0] || ssp->srcu_lock_nesting[1]); |
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flush_work(&ssp->srcu_work); |
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WARN_ON(ssp->srcu_gp_running); |
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WARN_ON(ssp->srcu_gp_waiting); |
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WARN_ON(ssp->srcu_cb_head); |
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WARN_ON(&ssp->srcu_cb_head != ssp->srcu_cb_tail); |
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WARN_ON(ssp->srcu_idx != ssp->srcu_idx_max); |
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WARN_ON(ssp->srcu_idx & 0x1); |
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} |
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EXPORT_SYMBOL_GPL(cleanup_srcu_struct); |
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/* |
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* Removes the count for the old reader from the appropriate element of |
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* the srcu_struct. |
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*/ |
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void __srcu_read_unlock(struct srcu_struct *ssp, int idx) |
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{ |
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int newval = ssp->srcu_lock_nesting[idx] - 1; |
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WRITE_ONCE(ssp->srcu_lock_nesting[idx], newval); |
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if (!newval && READ_ONCE(ssp->srcu_gp_waiting)) |
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swake_up_one(&ssp->srcu_wq); |
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} |
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EXPORT_SYMBOL_GPL(__srcu_read_unlock); |
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/* |
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* Workqueue handler to drive one grace period and invoke any callbacks |
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* that become ready as a result. Single-CPU and !PREEMPTION operation |
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* means that we get away with murder on synchronization. ;-) |
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*/ |
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void srcu_drive_gp(struct work_struct *wp) |
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{ |
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int idx; |
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struct rcu_head *lh; |
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struct rcu_head *rhp; |
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struct srcu_struct *ssp; |
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ssp = container_of(wp, struct srcu_struct, srcu_work); |
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if (ssp->srcu_gp_running || USHORT_CMP_GE(ssp->srcu_idx, READ_ONCE(ssp->srcu_idx_max))) |
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return; /* Already running or nothing to do. */ |
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/* Remove recently arrived callbacks and wait for readers. */ |
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WRITE_ONCE(ssp->srcu_gp_running, true); |
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local_irq_disable(); |
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lh = ssp->srcu_cb_head; |
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ssp->srcu_cb_head = NULL; |
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ssp->srcu_cb_tail = &ssp->srcu_cb_head; |
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local_irq_enable(); |
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idx = (ssp->srcu_idx & 0x2) / 2; |
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WRITE_ONCE(ssp->srcu_idx, ssp->srcu_idx + 1); |
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WRITE_ONCE(ssp->srcu_gp_waiting, true); /* srcu_read_unlock() wakes! */ |
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swait_event_exclusive(ssp->srcu_wq, !READ_ONCE(ssp->srcu_lock_nesting[idx])); |
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WRITE_ONCE(ssp->srcu_gp_waiting, false); /* srcu_read_unlock() cheap. */ |
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WRITE_ONCE(ssp->srcu_idx, ssp->srcu_idx + 1); |
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/* Invoke the callbacks we removed above. */ |
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while (lh) { |
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rhp = lh; |
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lh = lh->next; |
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local_bh_disable(); |
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rhp->func(rhp); |
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local_bh_enable(); |
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} |
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/* |
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* Enable rescheduling, and if there are more callbacks, |
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* reschedule ourselves. This can race with a call_srcu() |
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* at interrupt level, but the ->srcu_gp_running checks will |
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* straighten that out. |
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*/ |
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WRITE_ONCE(ssp->srcu_gp_running, false); |
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if (USHORT_CMP_LT(ssp->srcu_idx, READ_ONCE(ssp->srcu_idx_max))) |
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schedule_work(&ssp->srcu_work); |
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} |
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EXPORT_SYMBOL_GPL(srcu_drive_gp); |
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static void srcu_gp_start_if_needed(struct srcu_struct *ssp) |
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{ |
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unsigned short cookie; |
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cookie = get_state_synchronize_srcu(ssp); |
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if (USHORT_CMP_GE(READ_ONCE(ssp->srcu_idx_max), cookie)) |
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return; |
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WRITE_ONCE(ssp->srcu_idx_max, cookie); |
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if (!READ_ONCE(ssp->srcu_gp_running)) { |
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if (likely(srcu_init_done)) |
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schedule_work(&ssp->srcu_work); |
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else if (list_empty(&ssp->srcu_work.entry)) |
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list_add(&ssp->srcu_work.entry, &srcu_boot_list); |
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} |
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} |
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/* |
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* Enqueue an SRCU callback on the specified srcu_struct structure, |
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* initiating grace-period processing if it is not already running. |
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*/ |
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void call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp, |
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rcu_callback_t func) |
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{ |
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unsigned long flags; |
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rhp->func = func; |
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rhp->next = NULL; |
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local_irq_save(flags); |
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*ssp->srcu_cb_tail = rhp; |
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ssp->srcu_cb_tail = &rhp->next; |
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local_irq_restore(flags); |
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srcu_gp_start_if_needed(ssp); |
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} |
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EXPORT_SYMBOL_GPL(call_srcu); |
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/* |
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* synchronize_srcu - wait for prior SRCU read-side critical-section completion |
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*/ |
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void synchronize_srcu(struct srcu_struct *ssp) |
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{ |
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struct rcu_synchronize rs; |
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init_rcu_head_on_stack(&rs.head); |
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init_completion(&rs.completion); |
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call_srcu(ssp, &rs.head, wakeme_after_rcu); |
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wait_for_completion(&rs.completion); |
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destroy_rcu_head_on_stack(&rs.head); |
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} |
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EXPORT_SYMBOL_GPL(synchronize_srcu); |
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/* |
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* get_state_synchronize_srcu - Provide an end-of-grace-period cookie |
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*/ |
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unsigned long get_state_synchronize_srcu(struct srcu_struct *ssp) |
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{ |
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unsigned long ret; |
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barrier(); |
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ret = (READ_ONCE(ssp->srcu_idx) + 3) & ~0x1; |
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barrier(); |
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return ret & USHRT_MAX; |
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} |
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EXPORT_SYMBOL_GPL(get_state_synchronize_srcu); |
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/* |
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* start_poll_synchronize_srcu - Provide cookie and start grace period |
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* |
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* The difference between this and get_state_synchronize_srcu() is that |
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* this function ensures that the poll_state_synchronize_srcu() will |
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* eventually return the value true. |
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*/ |
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unsigned long start_poll_synchronize_srcu(struct srcu_struct *ssp) |
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{ |
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unsigned long ret = get_state_synchronize_srcu(ssp); |
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srcu_gp_start_if_needed(ssp); |
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return ret; |
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} |
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EXPORT_SYMBOL_GPL(start_poll_synchronize_srcu); |
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/* |
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* poll_state_synchronize_srcu - Has cookie's grace period ended? |
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*/ |
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bool poll_state_synchronize_srcu(struct srcu_struct *ssp, unsigned long cookie) |
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{ |
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bool ret = USHORT_CMP_GE(READ_ONCE(ssp->srcu_idx), cookie); |
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barrier(); |
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return ret; |
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} |
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EXPORT_SYMBOL_GPL(poll_state_synchronize_srcu); |
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/* Lockdep diagnostics. */ |
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void __init rcu_scheduler_starting(void) |
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{ |
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rcu_scheduler_active = RCU_SCHEDULER_RUNNING; |
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} |
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/* |
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* Queue work for srcu_struct structures with early boot callbacks. |
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* The work won't actually execute until the workqueue initialization |
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* phase that takes place after the scheduler starts. |
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*/ |
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void __init srcu_init(void) |
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{ |
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struct srcu_struct *ssp; |
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srcu_init_done = true; |
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while (!list_empty(&srcu_boot_list)) { |
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ssp = list_first_entry(&srcu_boot_list, |
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struct srcu_struct, srcu_work.entry); |
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list_del_init(&ssp->srcu_work.entry); |
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schedule_work(&ssp->srcu_work); |
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} |
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}
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