-stable review patch. If anyone has any objections, please let us know. ------------------ From: Andrew Morton [PATCH] cond_resched() fix 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 Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- kernel/sched.c | 25 +++++++++++++------------ 1 file changed, 13 insertions(+), 12 deletions(-) --- linux-2.6.17.7.orig/kernel/sched.c +++ linux-2.6.17.7/kernel/sched.c @@ -4044,17 +4044,22 @@ asmlinkage long sys_sched_yield(void) return 0; } -static inline void __cond_resched(void) +static inline int __resched_legal(int expected_preempt_count) +{ + if (unlikely(preempt_count() != expected_preempt_count)) + return 0; + if (unlikely(system_state != SYSTEM_RUNNING)) + return 0; + return 1; +} + +static void __cond_resched(void) { /* * The BKS might be reacquired before we have dropped * 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(); @@ -4064,13 +4069,12 @@ static inline void __cond_resched(void) int __sched cond_resched(void) { - if (need_resched()) { + if (need_resched() && __resched_legal(0)) { __cond_resched(); return 1; } return 0; } - EXPORT_SYMBOL(cond_resched); /* @@ -4091,7 +4095,7 @@ int cond_resched_lock(spinlock_t *lock) ret = 1; spin_lock(lock); } - if (need_resched()) { + if (need_resched() && __resched_legal(1)) { _raw_spin_unlock(lock); preempt_enable_no_resched(); __cond_resched(); @@ -4100,14 +4104,13 @@ 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(0)) { __local_bh_enable(); __cond_resched(); local_bh_disable(); @@ -4115,10 +4118,8 @@ int __sched cond_resched_softirq(void) } return 0; } - EXPORT_SYMBOL(cond_resched_softirq); - /** * yield - yield the current processor to other threads. * -- - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/