217 lines
6.5 KiB
C
217 lines
6.5 KiB
C
/*
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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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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, you can access it online at
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* http://www.gnu.org/licenses/gpl-2.0.html.
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*
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* Copyright (C) IBM Corporation, 2017
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*
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* Author: Paul McKenney <paulmck@us.ibm.com>
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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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static int init_srcu_struct_fields(struct srcu_struct *sp)
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{
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sp->srcu_lock_nesting[0] = 0;
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sp->srcu_lock_nesting[1] = 0;
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init_swait_queue_head(&sp->srcu_wq);
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sp->srcu_gp_seq = 0;
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rcu_segcblist_init(&sp->srcu_cblist);
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sp->srcu_gp_running = false;
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sp->srcu_gp_waiting = false;
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sp->srcu_idx = 0;
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INIT_WORK(&sp->srcu_work, srcu_drive_gp);
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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 *sp, 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 *)sp, sizeof(*sp));
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lockdep_init_map(&sp->dep_map, name, key, 0);
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return init_srcu_struct_fields(sp);
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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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* @sp: 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 *sp)
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{
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return init_srcu_struct_fields(sp);
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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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* @sp: 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 *sp)
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{
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WARN_ON(sp->srcu_lock_nesting[0] || sp->srcu_lock_nesting[1]);
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flush_work(&sp->srcu_work);
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WARN_ON(rcu_seq_state(sp->srcu_gp_seq));
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WARN_ON(sp->srcu_gp_running);
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WARN_ON(sp->srcu_gp_waiting);
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WARN_ON(!rcu_segcblist_empty(&sp->srcu_cblist));
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}
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EXPORT_SYMBOL_GPL(cleanup_srcu_struct);
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/*
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* Counts the new reader in the appropriate per-CPU element of the
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* srcu_struct. Must be called from process context.
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* Returns an index that must be passed to the matching srcu_read_unlock().
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*/
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int __srcu_read_lock(struct srcu_struct *sp)
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{
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int idx;
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idx = READ_ONCE(sp->srcu_idx);
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WRITE_ONCE(sp->srcu_lock_nesting[idx], sp->srcu_lock_nesting[idx] + 1);
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return idx;
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}
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EXPORT_SYMBOL_GPL(__srcu_read_lock);
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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. Must be called from process context.
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*/
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void __srcu_read_unlock(struct srcu_struct *sp, int idx)
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{
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int newval = sp->srcu_lock_nesting[idx] - 1;
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WRITE_ONCE(sp->srcu_lock_nesting[idx], newval);
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if (!newval && READ_ONCE(sp->srcu_gp_waiting))
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swake_up(&sp->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 !PREEMPT 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_cblist ready_cbs;
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struct srcu_struct *sp;
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struct rcu_head *rhp;
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sp = container_of(wp, struct srcu_struct, srcu_work);
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if (sp->srcu_gp_running || rcu_segcblist_empty(&sp->srcu_cblist))
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return; /* Already running or nothing to do. */
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/* Tag recently arrived callbacks and wait for readers. */
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WRITE_ONCE(sp->srcu_gp_running, true);
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rcu_segcblist_accelerate(&sp->srcu_cblist,
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rcu_seq_snap(&sp->srcu_gp_seq));
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rcu_seq_start(&sp->srcu_gp_seq);
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idx = sp->srcu_idx;
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WRITE_ONCE(sp->srcu_idx, !sp->srcu_idx);
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WRITE_ONCE(sp->srcu_gp_waiting, true); /* srcu_read_unlock() wakes! */
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swait_event(sp->srcu_wq, !READ_ONCE(sp->srcu_lock_nesting[idx]));
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WRITE_ONCE(sp->srcu_gp_waiting, false); /* srcu_read_unlock() cheap. */
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rcu_seq_end(&sp->srcu_gp_seq);
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/* Update callback list based on GP, and invoke ready callbacks. */
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rcu_segcblist_advance(&sp->srcu_cblist,
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rcu_seq_current(&sp->srcu_gp_seq));
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if (rcu_segcblist_ready_cbs(&sp->srcu_cblist)) {
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rcu_cblist_init(&ready_cbs);
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local_irq_disable();
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rcu_segcblist_extract_done_cbs(&sp->srcu_cblist, &ready_cbs);
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local_irq_enable();
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rhp = rcu_cblist_dequeue(&ready_cbs);
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for (; rhp != NULL; rhp = rcu_cblist_dequeue(&ready_cbs)) {
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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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local_irq_disable();
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rcu_segcblist_insert_count(&sp->srcu_cblist, &ready_cbs);
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local_irq_enable();
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}
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WRITE_ONCE(sp->srcu_gp_running, false);
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/*
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* If more callbacks, reschedule ourselves. This can race with
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* a call_srcu() at interrupt level, but the ->srcu_gp_running
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* checks will straighten that out.
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*/
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if (!rcu_segcblist_empty(&sp->srcu_cblist))
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schedule_work(&sp->srcu_work);
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}
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EXPORT_SYMBOL_GPL(srcu_drive_gp);
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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 *sp, struct rcu_head *head,
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rcu_callback_t func)
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{
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unsigned long flags;
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head->func = func;
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local_irq_save(flags);
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rcu_segcblist_enqueue(&sp->srcu_cblist, head, false);
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local_irq_restore(flags);
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if (!READ_ONCE(sp->srcu_gp_running))
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schedule_work(&sp->srcu_work);
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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 *sp)
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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(sp, &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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