2005-04-17 06:20:36 +08:00
|
|
|
/*
|
|
|
|
* Read-Copy Update mechanism for mutual exclusion
|
|
|
|
*
|
|
|
|
* This program is free software; you can redistribute it and/or modify
|
|
|
|
* it under the terms of the GNU General Public License as published by
|
|
|
|
* the Free Software Foundation; either version 2 of the License, or
|
|
|
|
* (at your option) any later version.
|
|
|
|
*
|
|
|
|
* This program is distributed in the hope that it will be useful,
|
|
|
|
* but WITHOUT ANY WARRANTY; without even the implied warranty of
|
|
|
|
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
|
|
|
|
* GNU General Public License for more details.
|
|
|
|
*
|
|
|
|
* You should have received a copy of the GNU General Public License
|
2013-12-04 02:02:52 +08:00
|
|
|
* along with this program; if not, you can access it online at
|
|
|
|
* http://www.gnu.org/licenses/gpl-2.0.html.
|
2005-04-17 06:20:36 +08:00
|
|
|
*
|
2008-01-26 04:08:24 +08:00
|
|
|
* Copyright IBM Corporation, 2001
|
2005-04-17 06:20:36 +08:00
|
|
|
*
|
|
|
|
* Authors: Dipankar Sarma <dipankar@in.ibm.com>
|
|
|
|
* Manfred Spraul <manfred@colorfullife.com>
|
2009-09-19 01:28:19 +08:00
|
|
|
*
|
2005-04-17 06:20:36 +08:00
|
|
|
* Based on the original work by Paul McKenney <paulmck@us.ibm.com>
|
|
|
|
* and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
|
|
|
|
* Papers:
|
|
|
|
* http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
|
|
|
|
* http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
|
|
|
|
*
|
|
|
|
* For detailed explanation of Read-Copy Update mechanism see -
|
2009-09-19 01:28:19 +08:00
|
|
|
* http://lse.sourceforge.net/locking/rcupdate.html
|
2005-04-17 06:20:36 +08:00
|
|
|
*
|
|
|
|
*/
|
|
|
|
#include <linux/types.h>
|
|
|
|
#include <linux/kernel.h>
|
|
|
|
#include <linux/init.h>
|
|
|
|
#include <linux/spinlock.h>
|
|
|
|
#include <linux/smp.h>
|
|
|
|
#include <linux/interrupt.h>
|
|
|
|
#include <linux/sched.h>
|
2011-07-27 07:09:06 +08:00
|
|
|
#include <linux/atomic.h>
|
2005-04-17 06:20:36 +08:00
|
|
|
#include <linux/bitops.h>
|
|
|
|
#include <linux/percpu.h>
|
|
|
|
#include <linux/notifier.h>
|
|
|
|
#include <linux/cpu.h>
|
2006-03-23 19:00:19 +08:00
|
|
|
#include <linux/mutex.h>
|
2011-05-24 02:51:41 +08:00
|
|
|
#include <linux/export.h>
|
2010-03-16 08:03:43 +08:00
|
|
|
#include <linux/hardirq.h>
|
2012-07-03 05:42:01 +08:00
|
|
|
#include <linux/delay.h>
|
2012-10-05 14:59:15 +08:00
|
|
|
#include <linux/module.h>
|
2005-04-17 06:20:36 +08:00
|
|
|
|
2011-06-18 06:53:19 +08:00
|
|
|
#define CREATE_TRACE_POINTS
|
|
|
|
|
|
|
|
#include "rcu.h"
|
|
|
|
|
2013-10-09 11:23:47 +08:00
|
|
|
MODULE_ALIAS("rcupdate");
|
|
|
|
#ifdef MODULE_PARAM_PREFIX
|
|
|
|
#undef MODULE_PARAM_PREFIX
|
|
|
|
#endif
|
|
|
|
#define MODULE_PARAM_PREFIX "rcupdate."
|
|
|
|
|
2012-10-05 14:59:15 +08:00
|
|
|
module_param(rcu_expedited, int, 0);
|
|
|
|
|
2012-04-14 03:54:22 +08:00
|
|
|
#ifdef CONFIG_PREEMPT_RCU
|
|
|
|
|
2012-05-22 02:58:36 +08:00
|
|
|
/*
|
|
|
|
* Preemptible RCU implementation for rcu_read_lock().
|
|
|
|
* Just increment ->rcu_read_lock_nesting, shared state will be updated
|
|
|
|
* if we block.
|
|
|
|
*/
|
|
|
|
void __rcu_read_lock(void)
|
|
|
|
{
|
|
|
|
current->rcu_read_lock_nesting++;
|
|
|
|
barrier(); /* critical section after entry code. */
|
|
|
|
}
|
|
|
|
EXPORT_SYMBOL_GPL(__rcu_read_lock);
|
|
|
|
|
|
|
|
/*
|
|
|
|
* Preemptible RCU implementation for rcu_read_unlock().
|
|
|
|
* Decrement ->rcu_read_lock_nesting. If the result is zero (outermost
|
|
|
|
* rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then
|
|
|
|
* invoke rcu_read_unlock_special() to clean up after a context switch
|
|
|
|
* in an RCU read-side critical section and other special cases.
|
|
|
|
*/
|
|
|
|
void __rcu_read_unlock(void)
|
|
|
|
{
|
|
|
|
struct task_struct *t = current;
|
|
|
|
|
|
|
|
if (t->rcu_read_lock_nesting != 1) {
|
|
|
|
--t->rcu_read_lock_nesting;
|
|
|
|
} else {
|
|
|
|
barrier(); /* critical section before exit code. */
|
|
|
|
t->rcu_read_lock_nesting = INT_MIN;
|
2012-07-03 05:42:01 +08:00
|
|
|
#ifdef CONFIG_PROVE_RCU_DELAY
|
|
|
|
udelay(10); /* Make preemption more probable. */
|
|
|
|
#endif /* #ifdef CONFIG_PROVE_RCU_DELAY */
|
2012-05-22 02:58:36 +08:00
|
|
|
barrier(); /* assign before ->rcu_read_unlock_special load */
|
|
|
|
if (unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))
|
|
|
|
rcu_read_unlock_special(t);
|
|
|
|
barrier(); /* ->rcu_read_unlock_special load before assign */
|
|
|
|
t->rcu_read_lock_nesting = 0;
|
|
|
|
}
|
|
|
|
#ifdef CONFIG_PROVE_LOCKING
|
|
|
|
{
|
|
|
|
int rrln = ACCESS_ONCE(t->rcu_read_lock_nesting);
|
|
|
|
|
|
|
|
WARN_ON_ONCE(rrln < 0 && rrln > INT_MIN / 2);
|
|
|
|
}
|
|
|
|
#endif /* #ifdef CONFIG_PROVE_LOCKING */
|
|
|
|
}
|
|
|
|
EXPORT_SYMBOL_GPL(__rcu_read_unlock);
|
|
|
|
|
2013-04-12 01:15:52 +08:00
|
|
|
#endif /* #ifdef CONFIG_PREEMPT_RCU */
|
2012-04-14 03:54:22 +08:00
|
|
|
|
2009-09-24 07:18:13 +08:00
|
|
|
#ifdef CONFIG_DEBUG_LOCK_ALLOC
|
|
|
|
static struct lock_class_key rcu_lock_key;
|
|
|
|
struct lockdep_map rcu_lock_map =
|
|
|
|
STATIC_LOCKDEP_MAP_INIT("rcu_read_lock", &rcu_lock_key);
|
|
|
|
EXPORT_SYMBOL_GPL(rcu_lock_map);
|
rcu: Introduce lockdep-based checking to RCU read-side primitives
Inspection is proving insufficient to catch all RCU misuses,
which is understandable given that rcu_dereference() might be
protected by any of four different flavors of RCU (RCU, RCU-bh,
RCU-sched, and SRCU), and might also/instead be protected by any
of a number of locking primitives. It is therefore time to
enlist the aid of lockdep.
This set of patches is inspired by earlier work by Peter
Zijlstra and Thomas Gleixner, and takes the following approach:
o Set up separate lockdep classes for RCU, RCU-bh, and RCU-sched.
o Set up separate lockdep classes for each instance of SRCU.
o Create primitives that check for being in an RCU read-side
critical section. These return exact answers if lockdep is
fully enabled, but if unsure, report being in an RCU read-side
critical section. (We want to avoid false positives!)
The primitives are:
For RCU: rcu_read_lock_held(void)
For RCU-bh: rcu_read_lock_bh_held(void)
For RCU-sched: rcu_read_lock_sched_held(void)
For SRCU: srcu_read_lock_held(struct srcu_struct *sp)
o Add rcu_dereference_check(), which takes a second argument
in which one places a boolean expression based on the above
primitives and/or lockdep_is_held().
o A new kernel configuration parameter, CONFIG_PROVE_RCU, enables
rcu_dereference_check(). This depends on CONFIG_PROVE_LOCKING,
and should be quite helpful during the transition period while
CONFIG_PROVE_RCU-unaware patches are in flight.
The existing rcu_dereference() primitive does no checking, but
upcoming patches will change that.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference: <1266887105-1528-1-git-send-email-paulmck@linux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2010-02-23 09:04:45 +08:00
|
|
|
|
|
|
|
static struct lock_class_key rcu_bh_lock_key;
|
|
|
|
struct lockdep_map rcu_bh_lock_map =
|
|
|
|
STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_bh", &rcu_bh_lock_key);
|
|
|
|
EXPORT_SYMBOL_GPL(rcu_bh_lock_map);
|
|
|
|
|
|
|
|
static struct lock_class_key rcu_sched_lock_key;
|
|
|
|
struct lockdep_map rcu_sched_lock_map =
|
|
|
|
STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_sched", &rcu_sched_lock_key);
|
|
|
|
EXPORT_SYMBOL_GPL(rcu_sched_lock_map);
|
2010-03-16 08:03:43 +08:00
|
|
|
|
2013-10-29 00:22:24 +08:00
|
|
|
static struct lock_class_key rcu_callback_key;
|
|
|
|
struct lockdep_map rcu_callback_map =
|
|
|
|
STATIC_LOCKDEP_MAP_INIT("rcu_callback", &rcu_callback_key);
|
|
|
|
EXPORT_SYMBOL_GPL(rcu_callback_map);
|
|
|
|
|
2013-08-31 13:04:07 +08:00
|
|
|
int notrace debug_lockdep_rcu_enabled(void)
|
2010-04-16 03:50:39 +08:00
|
|
|
{
|
|
|
|
return rcu_scheduler_active && debug_locks &&
|
|
|
|
current->lockdep_recursion == 0;
|
|
|
|
}
|
|
|
|
EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled);
|
|
|
|
|
2010-03-16 08:03:43 +08:00
|
|
|
/**
|
2010-04-29 05:39:09 +08:00
|
|
|
* rcu_read_lock_bh_held() - might we be in RCU-bh read-side critical section?
|
2010-03-16 08:03:43 +08:00
|
|
|
*
|
|
|
|
* Check for bottom half being disabled, which covers both the
|
|
|
|
* CONFIG_PROVE_RCU and not cases. Note that if someone uses
|
|
|
|
* rcu_read_lock_bh(), but then later enables BH, lockdep (if enabled)
|
2010-04-29 05:39:09 +08:00
|
|
|
* will show the situation. This is useful for debug checks in functions
|
|
|
|
* that require that they be called within an RCU read-side critical
|
|
|
|
* section.
|
2010-03-16 08:03:43 +08:00
|
|
|
*
|
|
|
|
* Check debug_lockdep_rcu_enabled() to prevent false positives during boot.
|
2012-01-24 04:41:26 +08:00
|
|
|
*
|
|
|
|
* Note that rcu_read_lock() is disallowed if the CPU is either idle or
|
|
|
|
* offline from an RCU perspective, so check for those as well.
|
2010-03-16 08:03:43 +08:00
|
|
|
*/
|
|
|
|
int rcu_read_lock_bh_held(void)
|
|
|
|
{
|
|
|
|
if (!debug_lockdep_rcu_enabled())
|
|
|
|
return 1;
|
2013-09-14 08:20:11 +08:00
|
|
|
if (!rcu_is_watching())
|
2011-10-08 07:25:18 +08:00
|
|
|
return 0;
|
2012-01-24 04:41:26 +08:00
|
|
|
if (!rcu_lockdep_current_cpu_online())
|
|
|
|
return 0;
|
2010-10-06 05:03:02 +08:00
|
|
|
return in_softirq() || irqs_disabled();
|
2010-03-16 08:03:43 +08:00
|
|
|
}
|
|
|
|
EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held);
|
|
|
|
|
|
|
|
#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
|
|
|
|
|
2011-05-27 13:14:36 +08:00
|
|
|
struct rcu_synchronize {
|
|
|
|
struct rcu_head head;
|
|
|
|
struct completion completion;
|
|
|
|
};
|
|
|
|
|
2008-02-14 07:03:15 +08:00
|
|
|
/*
|
|
|
|
* Awaken the corresponding synchronize_rcu() instance now that a
|
|
|
|
* grace period has elapsed.
|
|
|
|
*/
|
2011-05-27 13:14:36 +08:00
|
|
|
static void wakeme_after_rcu(struct rcu_head *head)
|
2006-03-08 13:55:33 +08:00
|
|
|
{
|
2008-01-26 04:08:24 +08:00
|
|
|
struct rcu_synchronize *rcu;
|
|
|
|
|
|
|
|
rcu = container_of(head, struct rcu_synchronize, head);
|
|
|
|
complete(&rcu->completion);
|
2006-03-08 13:55:33 +08:00
|
|
|
}
|
2010-05-07 00:28:41 +08:00
|
|
|
|
2011-05-27 13:14:36 +08:00
|
|
|
void wait_rcu_gp(call_rcu_func_t crf)
|
|
|
|
{
|
|
|
|
struct rcu_synchronize rcu;
|
|
|
|
|
|
|
|
init_rcu_head_on_stack(&rcu.head);
|
|
|
|
init_completion(&rcu.completion);
|
|
|
|
/* Will wake me after RCU finished. */
|
|
|
|
crf(&rcu.head, wakeme_after_rcu);
|
|
|
|
/* Wait for it. */
|
|
|
|
wait_for_completion(&rcu.completion);
|
|
|
|
destroy_rcu_head_on_stack(&rcu.head);
|
|
|
|
}
|
|
|
|
EXPORT_SYMBOL_GPL(wait_rcu_gp);
|
|
|
|
|
2010-04-17 20:48:42 +08:00
|
|
|
#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
|
|
|
|
static inline void debug_init_rcu_head(struct rcu_head *head)
|
|
|
|
{
|
|
|
|
debug_object_init(head, &rcuhead_debug_descr);
|
|
|
|
}
|
|
|
|
|
|
|
|
static inline void debug_rcu_head_free(struct rcu_head *head)
|
|
|
|
{
|
|
|
|
debug_object_free(head, &rcuhead_debug_descr);
|
|
|
|
}
|
|
|
|
|
|
|
|
/*
|
|
|
|
* fixup_activate is called when:
|
|
|
|
* - an active object is activated
|
|
|
|
* - an unknown object is activated (might be a statically initialized object)
|
|
|
|
* Activation is performed internally by call_rcu().
|
|
|
|
*/
|
|
|
|
static int rcuhead_fixup_activate(void *addr, enum debug_obj_state state)
|
|
|
|
{
|
|
|
|
struct rcu_head *head = addr;
|
|
|
|
|
|
|
|
switch (state) {
|
|
|
|
|
|
|
|
case ODEBUG_STATE_NOTAVAILABLE:
|
|
|
|
/*
|
|
|
|
* This is not really a fixup. We just make sure that it is
|
|
|
|
* tracked in the object tracker.
|
|
|
|
*/
|
|
|
|
debug_object_init(head, &rcuhead_debug_descr);
|
|
|
|
debug_object_activate(head, &rcuhead_debug_descr);
|
|
|
|
return 0;
|
|
|
|
default:
|
|
|
|
return 1;
|
|
|
|
}
|
|
|
|
}
|
|
|
|
|
|
|
|
/**
|
|
|
|
* init_rcu_head_on_stack() - initialize on-stack rcu_head for debugobjects
|
|
|
|
* @head: pointer to rcu_head structure to be initialized
|
|
|
|
*
|
|
|
|
* This function informs debugobjects of a new rcu_head structure that
|
|
|
|
* has been allocated as an auto variable on the stack. This function
|
|
|
|
* is not required for rcu_head structures that are statically defined or
|
|
|
|
* that are dynamically allocated on the heap. This function has no
|
|
|
|
* effect for !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
|
|
|
|
*/
|
|
|
|
void init_rcu_head_on_stack(struct rcu_head *head)
|
|
|
|
{
|
|
|
|
debug_object_init_on_stack(head, &rcuhead_debug_descr);
|
|
|
|
}
|
|
|
|
EXPORT_SYMBOL_GPL(init_rcu_head_on_stack);
|
|
|
|
|
|
|
|
/**
|
|
|
|
* destroy_rcu_head_on_stack() - destroy on-stack rcu_head for debugobjects
|
|
|
|
* @head: pointer to rcu_head structure to be initialized
|
|
|
|
*
|
|
|
|
* This function informs debugobjects that an on-stack rcu_head structure
|
|
|
|
* is about to go out of scope. As with init_rcu_head_on_stack(), this
|
|
|
|
* function is not required for rcu_head structures that are statically
|
|
|
|
* defined or that are dynamically allocated on the heap. Also as with
|
|
|
|
* init_rcu_head_on_stack(), this function has no effect for
|
|
|
|
* !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
|
|
|
|
*/
|
|
|
|
void destroy_rcu_head_on_stack(struct rcu_head *head)
|
|
|
|
{
|
|
|
|
debug_object_free(head, &rcuhead_debug_descr);
|
|
|
|
}
|
|
|
|
EXPORT_SYMBOL_GPL(destroy_rcu_head_on_stack);
|
|
|
|
|
|
|
|
struct debug_obj_descr rcuhead_debug_descr = {
|
|
|
|
.name = "rcu_head",
|
|
|
|
.fixup_activate = rcuhead_fixup_activate,
|
|
|
|
};
|
|
|
|
EXPORT_SYMBOL_GPL(rcuhead_debug_descr);
|
|
|
|
#endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */
|
2011-10-02 22:44:32 +08:00
|
|
|
|
|
|
|
#if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) || defined(CONFIG_RCU_TRACE)
|
2013-07-13 04:50:28 +08:00
|
|
|
void do_trace_rcu_torture_read(const char *rcutorturename, struct rcu_head *rhp,
|
2012-11-15 08:26:40 +08:00
|
|
|
unsigned long secs,
|
|
|
|
unsigned long c_old, unsigned long c)
|
2011-10-02 22:44:32 +08:00
|
|
|
{
|
2012-11-15 08:26:40 +08:00
|
|
|
trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c);
|
2011-10-02 22:44:32 +08:00
|
|
|
}
|
|
|
|
EXPORT_SYMBOL_GPL(do_trace_rcu_torture_read);
|
|
|
|
#else
|
2012-11-15 08:26:40 +08:00
|
|
|
#define do_trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c) \
|
|
|
|
do { } while (0)
|
2011-10-02 22:44:32 +08:00
|
|
|
#endif
|
2012-10-20 03:49:17 +08:00
|
|
|
|
|
|
|
#ifdef CONFIG_RCU_STALL_COMMON
|
|
|
|
|
|
|
|
#ifdef CONFIG_PROVE_RCU
|
|
|
|
#define RCU_STALL_DELAY_DELTA (5 * HZ)
|
|
|
|
#else
|
|
|
|
#define RCU_STALL_DELAY_DELTA 0
|
|
|
|
#endif
|
|
|
|
|
|
|
|
int rcu_cpu_stall_suppress __read_mostly; /* 1 = suppress stall warnings. */
|
2013-08-19 03:14:32 +08:00
|
|
|
static int rcu_cpu_stall_timeout __read_mostly = CONFIG_RCU_CPU_STALL_TIMEOUT;
|
2012-10-20 03:49:17 +08:00
|
|
|
|
|
|
|
module_param(rcu_cpu_stall_suppress, int, 0644);
|
|
|
|
module_param(rcu_cpu_stall_timeout, int, 0644);
|
|
|
|
|
|
|
|
int rcu_jiffies_till_stall_check(void)
|
|
|
|
{
|
|
|
|
int till_stall_check = ACCESS_ONCE(rcu_cpu_stall_timeout);
|
|
|
|
|
|
|
|
/*
|
|
|
|
* Limit check must be consistent with the Kconfig limits
|
|
|
|
* for CONFIG_RCU_CPU_STALL_TIMEOUT.
|
|
|
|
*/
|
|
|
|
if (till_stall_check < 3) {
|
|
|
|
ACCESS_ONCE(rcu_cpu_stall_timeout) = 3;
|
|
|
|
till_stall_check = 3;
|
|
|
|
} else if (till_stall_check > 300) {
|
|
|
|
ACCESS_ONCE(rcu_cpu_stall_timeout) = 300;
|
|
|
|
till_stall_check = 300;
|
|
|
|
}
|
|
|
|
return till_stall_check * HZ + RCU_STALL_DELAY_DELTA;
|
|
|
|
}
|
|
|
|
|
2014-04-27 14:15:35 +08:00
|
|
|
void rcu_sysrq_start(void)
|
|
|
|
{
|
|
|
|
if (!rcu_cpu_stall_suppress)
|
|
|
|
rcu_cpu_stall_suppress = 2;
|
|
|
|
}
|
|
|
|
|
|
|
|
void rcu_sysrq_end(void)
|
|
|
|
{
|
|
|
|
if (rcu_cpu_stall_suppress == 2)
|
|
|
|
rcu_cpu_stall_suppress = 0;
|
|
|
|
}
|
|
|
|
|
2012-10-20 03:49:17 +08:00
|
|
|
static int rcu_panic(struct notifier_block *this, unsigned long ev, void *ptr)
|
|
|
|
{
|
|
|
|
rcu_cpu_stall_suppress = 1;
|
|
|
|
return NOTIFY_DONE;
|
|
|
|
}
|
|
|
|
|
|
|
|
static struct notifier_block rcu_panic_block = {
|
|
|
|
.notifier_call = rcu_panic,
|
|
|
|
};
|
|
|
|
|
|
|
|
static int __init check_cpu_stall_init(void)
|
|
|
|
{
|
|
|
|
atomic_notifier_chain_register(&panic_notifier_list, &rcu_panic_block);
|
|
|
|
return 0;
|
|
|
|
}
|
|
|
|
early_initcall(check_cpu_stall_init);
|
|
|
|
|
|
|
|
#endif /* #ifdef CONFIG_RCU_STALL_COMMON */
|
sched,rcu: Make cond_resched() report RCU quiescent states
Given a CPU running a loop containing cond_resched(), with no
other tasks runnable on that CPU, RCU will eventually report RCU
CPU stall warnings due to lack of quiescent states. Fortunately,
every call to cond_resched() is a perfectly good quiescent state.
Unfortunately, invoking rcu_note_context_switch() is a bit heavyweight
for cond_resched(), especially given the need to disable preemption,
and, for RCU-preempt, interrupts as well.
This commit therefore maintains a per-CPU counter that causes
cond_resched(), cond_resched_lock(), and cond_resched_softirq() to call
rcu_note_context_switch(), but only about once per 256 invocations.
This ratio was chosen in keeping with the relative time constants of
RCU grace periods.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2014-03-17 12:36:25 +08:00
|
|
|
|
|
|
|
/*
|
|
|
|
* Hooks for cond_resched() and friends to avoid RCU CPU stall warnings.
|
|
|
|
*/
|
|
|
|
|
|
|
|
DEFINE_PER_CPU(int, rcu_cond_resched_count);
|
|
|
|
|
|
|
|
/*
|
|
|
|
* Report a set of RCU quiescent states, for use by cond_resched()
|
|
|
|
* and friends. Out of line due to being called infrequently.
|
|
|
|
*/
|
|
|
|
void rcu_resched(void)
|
|
|
|
{
|
|
|
|
preempt_disable();
|
|
|
|
__this_cpu_write(rcu_cond_resched_count, 0);
|
|
|
|
rcu_note_context_switch(smp_processor_id());
|
|
|
|
preempt_enable();
|
|
|
|
}
|