From: Andrew Morton Fix a bug identified by Zou Nan hai : 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 Cc: Signed-off-by: Andrew Morton --- kernel/sched.c | 25 +++++++++++++------------ 1 file changed, 13 insertions(+), 12 deletions(-) diff -puN kernel/sched.c~cond_resched-fix kernel/sched.c --- a/kernel/sched.c~cond_resched-fix +++ a/kernel/sched.c @@ -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. * _