242 lines
6.2 KiB
C
242 lines
6.2 KiB
C
/*
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* Read-Copy Update mechanism for mutual exclusion, the Bloatwatch edition.
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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 IBM Corporation, 2008
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*
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* Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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*
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* For detailed explanation of Read-Copy Update mechanism see -
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* Documentation/RCU
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*/
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#include <linux/completion.h>
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#include <linux/interrupt.h>
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#include <linux/notifier.h>
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#include <linux/rcupdate_wait.h>
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#include <linux/kernel.h>
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#include <linux/export.h>
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#include <linux/mutex.h>
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#include <linux/sched.h>
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#include <linux/types.h>
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#include <linux/init.h>
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#include <linux/time.h>
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#include <linux/cpu.h>
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#include <linux/prefetch.h>
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#include "rcu.h"
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/* Global control variables for rcupdate callback mechanism. */
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struct rcu_ctrlblk {
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struct rcu_head *rcucblist; /* List of pending callbacks (CBs). */
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struct rcu_head **donetail; /* ->next pointer of last "done" CB. */
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struct rcu_head **curtail; /* ->next pointer of last CB. */
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};
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/* Definition for rcupdate control block. */
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static struct rcu_ctrlblk rcu_sched_ctrlblk = {
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.donetail = &rcu_sched_ctrlblk.rcucblist,
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.curtail = &rcu_sched_ctrlblk.rcucblist,
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};
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static struct rcu_ctrlblk rcu_bh_ctrlblk = {
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.donetail = &rcu_bh_ctrlblk.rcucblist,
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.curtail = &rcu_bh_ctrlblk.rcucblist,
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};
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void rcu_barrier_bh(void)
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{
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wait_rcu_gp(call_rcu_bh);
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}
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EXPORT_SYMBOL(rcu_barrier_bh);
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void rcu_barrier_sched(void)
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{
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wait_rcu_gp(call_rcu_sched);
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}
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EXPORT_SYMBOL(rcu_barrier_sched);
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/*
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* Helper function for rcu_sched_qs() and rcu_bh_qs().
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* Also irqs are disabled to avoid confusion due to interrupt handlers
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* invoking call_rcu().
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*/
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static int rcu_qsctr_help(struct rcu_ctrlblk *rcp)
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{
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if (rcp->donetail != rcp->curtail) {
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rcp->donetail = rcp->curtail;
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return 1;
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}
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return 0;
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}
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/*
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* Record an rcu quiescent state. And an rcu_bh quiescent state while we
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* are at it, given that any rcu quiescent state is also an rcu_bh
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* quiescent state. Use "+" instead of "||" to defeat short circuiting.
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*/
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void rcu_sched_qs(void)
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{
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unsigned long flags;
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local_irq_save(flags);
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if (rcu_qsctr_help(&rcu_sched_ctrlblk) +
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rcu_qsctr_help(&rcu_bh_ctrlblk))
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raise_softirq(RCU_SOFTIRQ);
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local_irq_restore(flags);
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}
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/*
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* Record an rcu_bh quiescent state.
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*/
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void rcu_bh_qs(void)
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{
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unsigned long flags;
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local_irq_save(flags);
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if (rcu_qsctr_help(&rcu_bh_ctrlblk))
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raise_softirq(RCU_SOFTIRQ);
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local_irq_restore(flags);
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}
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/*
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* Check to see if the scheduling-clock interrupt came from an extended
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* quiescent state, and, if so, tell RCU about it. This function must
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* be called from hardirq context. It is normally called from the
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* scheduling-clock interrupt.
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*/
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void rcu_check_callbacks(int user)
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{
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if (user)
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rcu_sched_qs();
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else if (!in_softirq())
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rcu_bh_qs();
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if (user)
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rcu_note_voluntary_context_switch(current);
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}
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/*
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* Invoke the RCU callbacks on the specified rcu_ctrlkblk structure
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* whose grace period has elapsed.
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*/
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static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
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{
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struct rcu_head *next, *list;
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unsigned long flags;
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/* Move the ready-to-invoke callbacks to a local list. */
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local_irq_save(flags);
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if (rcp->donetail == &rcp->rcucblist) {
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/* No callbacks ready, so just leave. */
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local_irq_restore(flags);
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return;
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}
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list = rcp->rcucblist;
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rcp->rcucblist = *rcp->donetail;
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*rcp->donetail = NULL;
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if (rcp->curtail == rcp->donetail)
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rcp->curtail = &rcp->rcucblist;
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rcp->donetail = &rcp->rcucblist;
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local_irq_restore(flags);
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/* Invoke the callbacks on the local list. */
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while (list) {
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next = list->next;
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prefetch(next);
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debug_rcu_head_unqueue(list);
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local_bh_disable();
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__rcu_reclaim("", list);
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local_bh_enable();
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list = next;
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}
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}
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static __latent_entropy void rcu_process_callbacks(struct softirq_action *unused)
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{
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__rcu_process_callbacks(&rcu_sched_ctrlblk);
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__rcu_process_callbacks(&rcu_bh_ctrlblk);
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}
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/*
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* Wait for a grace period to elapse. But it is illegal to invoke
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* synchronize_sched() from within an RCU read-side critical section.
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* Therefore, any legal call to synchronize_sched() is a quiescent
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* state, and so on a UP system, synchronize_sched() need do nothing.
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* Ditto for synchronize_rcu_bh(). (But Lai Jiangshan points out the
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* benefits of doing might_sleep() to reduce latency.)
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*
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* Cool, huh? (Due to Josh Triplett.)
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*/
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void synchronize_sched(void)
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{
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RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
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lock_is_held(&rcu_lock_map) ||
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lock_is_held(&rcu_sched_lock_map),
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"Illegal synchronize_sched() in RCU read-side critical section");
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}
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EXPORT_SYMBOL_GPL(synchronize_sched);
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/*
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* Helper function for call_rcu() and call_rcu_bh().
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*/
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static void __call_rcu(struct rcu_head *head,
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rcu_callback_t func,
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struct rcu_ctrlblk *rcp)
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{
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unsigned long flags;
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debug_rcu_head_queue(head);
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head->func = func;
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head->next = NULL;
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local_irq_save(flags);
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*rcp->curtail = head;
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rcp->curtail = &head->next;
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local_irq_restore(flags);
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if (unlikely(is_idle_task(current))) {
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/* force scheduling for rcu_sched_qs() */
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resched_cpu(0);
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}
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}
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/*
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* Post an RCU callback to be invoked after the end of an RCU-sched grace
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* period. But since we have but one CPU, that would be after any
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* quiescent state.
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*/
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void call_rcu_sched(struct rcu_head *head, rcu_callback_t func)
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{
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__call_rcu(head, func, &rcu_sched_ctrlblk);
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}
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EXPORT_SYMBOL_GPL(call_rcu_sched);
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/*
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* Post an RCU bottom-half callback to be invoked after any subsequent
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* quiescent state.
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*/
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void call_rcu_bh(struct rcu_head *head, rcu_callback_t func)
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{
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__call_rcu(head, func, &rcu_bh_ctrlblk);
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}
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EXPORT_SYMBOL_GPL(call_rcu_bh);
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void __init rcu_init(void)
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{
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open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
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rcu_early_boot_tests();
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}
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