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Commit e7b38404 authored by Andrew Morton's avatar Andrew Morton Committed by Linus Torvalds
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[PATCH] cond_resched() fix 



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: default avatarIngo Molnar <mingo@elte.hu>
Cc: <stable@kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 92fe15a3

kernel/sched.c

+13 −12
Original line number Diff line number Diff line
@@ -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.

 *