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![Paul E. McKenney](/assets/img/avatar_default.png)
RCU, RCU-bh, and RCU-sched read-side critical sections are forbidden in the inner idle loop, that is, between the rcu_idle_enter() and the rcu_idle_exit() -- RCU will happily ignore any such read-side critical sections. However, things like powertop need tracepoints in the inner idle loop. This commit therefore provides an RCU_NONIDLE() macro that can be used to wrap code in the idle loop that requires RCU read-side critical sections. Suggested-by: Steven Rostedt <rostedt@goodmis.org> Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org> Acked-by: Deepthi Dharwar <deepthi@linux.vnet.ibm.com>
379 lines
10 KiB
C
379 lines
10 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/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/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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#ifdef CONFIG_RCU_TRACE
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#include <trace/events/rcu.h>
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#endif /* #else #ifdef CONFIG_RCU_TRACE */
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#include "rcu.h"
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/* Forward declarations for rcutiny_plugin.h. */
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struct rcu_ctrlblk;
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static void invoke_rcu_callbacks(void);
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static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp);
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static void rcu_process_callbacks(struct softirq_action *unused);
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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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static long long rcu_dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
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/* Common code for rcu_idle_enter() and rcu_irq_exit(), see kernel/rcutree.c. */
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static void rcu_idle_enter_common(long long oldval)
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{
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if (rcu_dynticks_nesting) {
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RCU_TRACE(trace_rcu_dyntick("--=",
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oldval, rcu_dynticks_nesting));
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return;
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}
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RCU_TRACE(trace_rcu_dyntick("Start", oldval, rcu_dynticks_nesting));
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if (!is_idle_task(current)) {
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struct task_struct *idle = idle_task(smp_processor_id());
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RCU_TRACE(trace_rcu_dyntick("Error on entry: not idle task",
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oldval, rcu_dynticks_nesting));
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ftrace_dump(DUMP_ALL);
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WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
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current->pid, current->comm,
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idle->pid, idle->comm); /* must be idle task! */
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}
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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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* Enter idle, which is an extended quiescent state if we have fully
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* entered that mode (i.e., if the new value of dynticks_nesting is zero).
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*/
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void rcu_idle_enter(void)
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{
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unsigned long flags;
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long long oldval;
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local_irq_save(flags);
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oldval = rcu_dynticks_nesting;
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WARN_ON_ONCE((rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK) == 0);
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if ((rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK) ==
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DYNTICK_TASK_NEST_VALUE)
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rcu_dynticks_nesting = 0;
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else
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rcu_dynticks_nesting -= DYNTICK_TASK_NEST_VALUE;
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rcu_idle_enter_common(oldval);
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local_irq_restore(flags);
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}
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EXPORT_SYMBOL_GPL(rcu_idle_enter);
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/*
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* Exit an interrupt handler towards idle.
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*/
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void rcu_irq_exit(void)
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{
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unsigned long flags;
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long long oldval;
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local_irq_save(flags);
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oldval = rcu_dynticks_nesting;
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rcu_dynticks_nesting--;
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WARN_ON_ONCE(rcu_dynticks_nesting < 0);
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rcu_idle_enter_common(oldval);
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local_irq_restore(flags);
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}
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/* Common code for rcu_idle_exit() and rcu_irq_enter(), see kernel/rcutree.c. */
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static void rcu_idle_exit_common(long long oldval)
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{
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if (oldval) {
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RCU_TRACE(trace_rcu_dyntick("++=",
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oldval, rcu_dynticks_nesting));
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return;
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}
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RCU_TRACE(trace_rcu_dyntick("End", oldval, rcu_dynticks_nesting));
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if (!is_idle_task(current)) {
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struct task_struct *idle = idle_task(smp_processor_id());
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RCU_TRACE(trace_rcu_dyntick("Error on exit: not idle task",
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oldval, rcu_dynticks_nesting));
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ftrace_dump(DUMP_ALL);
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WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
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current->pid, current->comm,
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idle->pid, idle->comm); /* must be idle task! */
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}
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}
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/*
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* Exit idle, so that we are no longer in an extended quiescent state.
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*/
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void rcu_idle_exit(void)
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{
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unsigned long flags;
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long long oldval;
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local_irq_save(flags);
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oldval = rcu_dynticks_nesting;
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WARN_ON_ONCE(rcu_dynticks_nesting < 0);
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if (rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK)
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rcu_dynticks_nesting += DYNTICK_TASK_NEST_VALUE;
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else
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rcu_dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
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rcu_idle_exit_common(oldval);
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local_irq_restore(flags);
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}
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EXPORT_SYMBOL_GPL(rcu_idle_exit);
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/*
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* Enter an interrupt handler, moving away from idle.
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*/
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void rcu_irq_enter(void)
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{
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unsigned long flags;
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long long oldval;
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local_irq_save(flags);
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oldval = rcu_dynticks_nesting;
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rcu_dynticks_nesting++;
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WARN_ON_ONCE(rcu_dynticks_nesting == 0);
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rcu_idle_exit_common(oldval);
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local_irq_restore(flags);
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}
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#ifdef CONFIG_PROVE_RCU
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/*
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* Test whether RCU thinks that the current CPU is idle.
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*/
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int rcu_is_cpu_idle(void)
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{
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return !rcu_dynticks_nesting;
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}
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EXPORT_SYMBOL(rcu_is_cpu_idle);
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#endif /* #ifdef CONFIG_PROVE_RCU */
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/*
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* Test whether the current CPU was interrupted from idle. Nested
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* interrupts don't count, we must be running at the first interrupt
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* level.
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*/
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int rcu_is_cpu_rrupt_from_idle(void)
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{
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return rcu_dynticks_nesting <= 0;
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}
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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->rcucblist != NULL &&
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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(int cpu)
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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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invoke_rcu_callbacks();
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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(int cpu)
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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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invoke_rcu_callbacks();
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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 cpu, int user)
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{
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if (user || rcu_is_cpu_rrupt_from_idle())
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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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char *rn = NULL;
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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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RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, 0, -1));
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RCU_TRACE(trace_rcu_batch_end(rcp->name, 0,
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ACCESS_ONCE(rcp->rcucblist),
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need_resched(),
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is_idle_task(current),
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rcu_is_callbacks_kthread()));
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return;
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}
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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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RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, rcp->qlen, -1));
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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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RCU_TRACE(rn = rcp->name);
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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(rn, 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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RCU_TRACE(trace_rcu_batch_end(rcp->name, cb_count, 0, need_resched(),
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is_idle_task(current),
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rcu_is_callbacks_kthread()));
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}
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static 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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rcu_preempt_process_callbacks();
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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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rcu_lockdep_assert(!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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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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