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[PATCH] cond_resched() fix

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Fix a bug identified by Zou Nan hai <nanhai.zou@intel.com>:

If the system is in state SYSTEM_BOOTING, and need_resched() is true,
cond_resched() returns true even though it didn't reschedule.  Consequently
need_resched() remains true and JBD locks up.

Fix that by teaching cond_resched() to only return true if it really did call
schedule().

cond_resched_lock() and cond_resched_softirq() have a problem too.  If we're
in SYSTEM_BOOTING state and need_resched() is true, these functions will drop
the lock and will then try to call schedule(), but the SYSTEM_BOOTING state
will prevent schedule() from being called.  So on return, need_resched() will
still be true, but cond_resched_lock() has to return 1 to tell the caller that
the lock was dropped.  The caller will probably lock up.

Bottom line: if these functions dropped the lock, they _must_ call schedule()
to clear need_resched().   Make it so.

Also, uninline __cond_resched().  It's largeish, and slowpath.

Acked-by: Ingo Molnar <mingo@elte.hu>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Andrew Morton 2006-06-30 01:56:00 -07:00 committed by Linus Torvalds
parent 92fe15a3d2
commit e7b384043e
1 changed files with 13 additions and 12 deletions
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25
kernel/sched.c
View file

@ -4386,7 +4386,16 @@ asmlinkage long sys_sched_yield(void)
return 0;
}
static inline void __cond_resched(void)
static inline int __resched_legal(void)
{
if (unlikely(preempt_count()))
return 0;
if (unlikely(system_state != SYSTEM_RUNNING))
return 0;
return 1;
}
static void __cond_resched(void)
{
#ifdef CONFIG_DEBUG_SPINLOCK_SLEEP
__might_sleep(__FILE__, __LINE__);
@ -4396,10 +4405,6 @@ static inline void __cond_resched(void)
* PREEMPT_ACTIVE, which could trigger a second
* cond_resched() call.
*/
if (unlikely(preempt_count()))
return;
if (unlikely(system_state != SYSTEM_RUNNING))
return;
do {
add_preempt_count(PREEMPT_ACTIVE);
schedule();
@ -4409,13 +4414,12 @@ static inline void __cond_resched(void)
int __sched cond_resched(void)
{
if (need_resched()) {
if (need_resched() && __resched_legal()) {
__cond_resched();
return 1;
}
return 0;
}
EXPORT_SYMBOL(cond_resched);
/*
@ -4436,7 +4440,7 @@ int cond_resched_lock(spinlock_t *lock)
ret = 1;
spin_lock(lock);
}
if (need_resched()) {
if (need_resched() && __resched_legal()) {
_raw_spin_unlock(lock);
preempt_enable_no_resched();
__cond_resched();
@ -4445,14 +4449,13 @@ int cond_resched_lock(spinlock_t *lock)
}
return ret;
}
EXPORT_SYMBOL(cond_resched_lock);
int __sched cond_resched_softirq(void)
{
BUG_ON(!in_softirq());
if (need_resched()) {
if (need_resched() && __resched_legal()) {
__local_bh_enable();
__cond_resched();
local_bh_disable();
@ -4460,10 +4463,8 @@ int __sched cond_resched_softirq(void)
}
return 0;
}
EXPORT_SYMBOL(cond_resched_softirq);
/**
* yield - yield the current processor to other threads.
*