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b24efdfdf6
If the RCU callback-processing kthread has nothing to do, it parks in a wait_event(). If RCU remains idle for more than two minutes, the kernel complains about this. This commit changes from wait_event() to wait_event_interruptible() to prevent the kernel from complaining just because RCU is idle. Reported-by: Russell King <rmk+kernel@arm.linux.org.uk> Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Tested-by: Thomas Weber <weber@corscience.de> Tested-by: Russell King <rmk+kernel@arm.linux.org.uk>
325 lines
8.4 KiB
C
325 lines
8.4 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, write to the Free Software
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* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
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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/moduleparam.h>
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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.h>
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#include <linux/kernel.h>
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#include <linux/module.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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/* Controls for rcu_kthread() kthread, replacing RCU_SOFTIRQ used previously. */
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static struct task_struct *rcu_kthread_task;
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static DECLARE_WAIT_QUEUE_HEAD(rcu_kthread_wq);
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static unsigned long have_rcu_kthread_work;
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static void invoke_rcu_kthread(void);
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/* Forward declarations for rcutiny_plugin.h. */
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struct rcu_ctrlblk;
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static void rcu_process_callbacks(struct rcu_ctrlblk *rcp);
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static int rcu_kthread(void *arg);
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static void __call_rcu(struct rcu_head *head,
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void (*func)(struct rcu_head *rcu),
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struct rcu_ctrlblk *rcp);
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#include "rcutiny_plugin.h"
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#ifdef CONFIG_NO_HZ
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static long rcu_dynticks_nesting = 1;
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/*
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* Enter dynticks-idle mode, which is an extended quiescent state
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* if we have fully entered that mode (i.e., if the new value of
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* dynticks_nesting is zero).
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*/
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void rcu_enter_nohz(void)
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{
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if (--rcu_dynticks_nesting == 0)
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rcu_sched_qs(0); /* implies rcu_bh_qsctr_inc(0) */
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}
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/*
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* Exit dynticks-idle mode, so that we are no longer in an extended
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* quiescent state.
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*/
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void rcu_exit_nohz(void)
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{
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rcu_dynticks_nesting++;
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}
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#endif /* #ifdef CONFIG_NO_HZ */
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/*
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* Helper function for rcu_qsctr_inc() and rcu_bh_qsctr_inc().
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* Also disable irqs 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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unsigned long flags;
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local_irq_save(flags);
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if (rcp->rcucblist != NULL &&
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rcp->donetail != rcp->curtail) {
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rcp->donetail = rcp->curtail;
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local_irq_restore(flags);
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return 1;
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}
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local_irq_restore(flags);
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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(int cpu)
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{
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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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invoke_rcu_kthread();
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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(int cpu)
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{
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if (rcu_qsctr_help(&rcu_bh_ctrlblk))
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invoke_rcu_kthread();
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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.
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*/
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void rcu_check_callbacks(int cpu, int user)
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{
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if (user ||
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(idle_cpu(cpu) &&
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!in_softirq() &&
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hardirq_count() <= (1 << HARDIRQ_SHIFT)))
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rcu_sched_qs(cpu);
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else if (!in_softirq())
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rcu_bh_qs(cpu);
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rcu_preempt_check_callbacks();
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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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RCU_TRACE(int cb_count = 0);
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/* If no RCU callbacks ready to invoke, just return. */
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if (&rcp->rcucblist == rcp->donetail)
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return;
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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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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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rcu_preempt_remove_callbacks(rcp);
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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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list->func(list);
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local_bh_enable();
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list = next;
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RCU_TRACE(cb_count++);
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}
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RCU_TRACE(rcu_trace_sub_qlen(rcp, cb_count));
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}
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/*
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* This kthread invokes RCU callbacks whose grace periods have
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* elapsed. It is awakened as needed, and takes the place of the
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* RCU_SOFTIRQ that was used previously for this purpose.
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* This is a kthread, but it is never stopped, at least not until
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* the system goes down.
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*/
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static int rcu_kthread(void *arg)
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{
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unsigned long work;
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unsigned long morework;
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unsigned long flags;
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for (;;) {
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wait_event_interruptible(rcu_kthread_wq,
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have_rcu_kthread_work != 0);
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morework = rcu_boost();
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local_irq_save(flags);
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work = have_rcu_kthread_work;
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have_rcu_kthread_work = morework;
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local_irq_restore(flags);
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if (work) {
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rcu_process_callbacks(&rcu_sched_ctrlblk);
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rcu_process_callbacks(&rcu_bh_ctrlblk);
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rcu_preempt_process_callbacks();
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}
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schedule_timeout_interruptible(1); /* Leave CPU for others. */
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}
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return 0; /* Not reached, but needed to shut gcc up. */
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}
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/*
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* Wake up rcu_kthread() to process callbacks now eligible for invocation
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* or to boost readers.
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*/
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static void invoke_rcu_kthread(void)
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{
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unsigned long flags;
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local_irq_save(flags);
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have_rcu_kthread_work = 1;
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wake_up(&rcu_kthread_wq);
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local_irq_restore(flags);
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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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* But we want to make this a static inline later. The cond_resched()
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* currently makes this problematic.
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*/
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void synchronize_sched(void)
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{
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cond_resched();
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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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void (*func)(struct rcu_head *rcu),
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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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RCU_TRACE(rcp->qlen++);
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local_irq_restore(flags);
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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, void (*func)(struct rcu_head *rcu))
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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, void (*func)(struct rcu_head *rcu))
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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 rcu_barrier_bh(void)
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{
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struct rcu_synchronize rcu;
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init_rcu_head_on_stack(&rcu.head);
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init_completion(&rcu.completion);
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/* Will wake me after RCU finished. */
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call_rcu_bh(&rcu.head, wakeme_after_rcu);
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/* Wait for it. */
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wait_for_completion(&rcu.completion);
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destroy_rcu_head_on_stack(&rcu.head);
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}
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EXPORT_SYMBOL_GPL(rcu_barrier_bh);
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void rcu_barrier_sched(void)
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{
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struct rcu_synchronize rcu;
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init_rcu_head_on_stack(&rcu.head);
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init_completion(&rcu.completion);
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/* Will wake me after RCU finished. */
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call_rcu_sched(&rcu.head, wakeme_after_rcu);
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/* Wait for it. */
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wait_for_completion(&rcu.completion);
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destroy_rcu_head_on_stack(&rcu.head);
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}
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EXPORT_SYMBOL_GPL(rcu_barrier_sched);
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/*
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* Spawn the kthread that invokes RCU callbacks.
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*/
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static int __init rcu_spawn_kthreads(void)
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{
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struct sched_param sp;
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rcu_kthread_task = kthread_run(rcu_kthread, NULL, "rcu_kthread");
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sp.sched_priority = RCU_BOOST_PRIO;
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sched_setscheduler_nocheck(rcu_kthread_task, SCHED_FIFO, &sp);
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return 0;
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}
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early_initcall(rcu_spawn_kthreads);
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