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