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Hi. Can you confirm that the problem I mentioned in http://lkml.org/lkml/2006/12/24/32 is the same? Best regards, Fabio On 12/26/06, Ingo Molnar <mingo@elte.hu> wrote: > > * Ingo Molnar <mingo@elte.hu> wrote: > > > > I've had at least one more occurrence of it: > > > > > > [ 78.804940] BUG: scheduling while atomic: kbd/0x20000000/3444 > > > [ 78.804944] > > > [ 78.804945] Call Trace: > > > > ok, i can think of a simpler scenario: > > add_preempt_count(PREEMPT_ACTIVE) /twice/, nested into each other. > > doh - the BKL! That does a down() in a PREEMPT_ACTIVE section, which can > trigger cond_resched(). The fix is to check for PREEMPT_ACTIVE in > cond_resched(). (and only in cond_resched()) > > Updated fix (against -rc2) attached. > > Ingo > > ----------------------> > Subject: [patch] sched: fix cond_resched_softirq() offset > From: Ingo Molnar <mingo@elte.hu> > > remove the __resched_legal() check: it is conceptually broken. > The biggest problem it had is that it can mask buggy cond_resched() > calls. A cond_resched() call is only legal if we are not in an > atomic context, with two narrow exceptions: > > - if the system is booting > - a reacquire_kernel_lock() down() done while PREEMPT_ACTIVE is set > > But __resched_legal() hid this and just silently returned whenever > these primitives were called from invalid contexts. (Same goes for > cond_resched_locked() and cond_resched_softirq()). > > furthermore, the __legal_resched(0) call was buggy in that it caused > unnecessarily long softirq latencies via cond_resched_softirq(). (which > is only called from softirq-off sections, hence the code did nothing.) > > the fix is to resurrect the efficiency of the might_sleep checks and to > only allow the narrow exceptions. > > Signed-off-by: Ingo Molnar <mingo@elte.hu> > --- > kernel/sched.c | 18 ++++-------------- > 1 file changed, 4 insertions(+), 14 deletions(-) > > Index: linux/kernel/sched.c > =================================================================== > --- linux.orig/kernel/sched.c > +++ linux/kernel/sched.c > @@ -4617,17 +4617,6 @@ asmlinkage long sys_sched_yield(void) > return 0; > } > > -static inline int __resched_legal(int expected_preempt_count) > -{ > -#ifdef CONFIG_PREEMPT > - if (unlikely(preempt_count() != expected_preempt_count)) > - return 0; > -#endif > - if (unlikely(system_state != SYSTEM_RUNNING)) > - return 0; > - return 1; > -} > - > static void __cond_resched(void) > { > #ifdef CONFIG_DEBUG_SPINLOCK_SLEEP > @@ -4647,7 +4636,8 @@ static void __cond_resched(void) > > int __sched cond_resched(void) > { > - if (need_resched() && __resched_legal(0)) { > + if (need_resched() && !(preempt_count() & PREEMPT_ACTIVE) && > + system_state == SYSTEM_RUNNING) { > __cond_resched(); > return 1; > } > @@ -4673,7 +4663,7 @@ int cond_resched_lock(spinlock_t *lock) > ret = 1; > spin_lock(lock); > } > - if (need_resched() && __resched_legal(1)) { > + if (need_resched() && system_state == SYSTEM_RUNNING) { > spin_release(&lock->dep_map, 1, _THIS_IP_); > _raw_spin_unlock(lock); > preempt_enable_no_resched(); > @@ -4689,7 +4679,7 @@ int __sched cond_resched_softirq(void) > { > BUG_ON(!in_softirq()); > > - if (need_resched() && __resched_legal(0)) { > + if (need_resched() && system_state == SYSTEM_RUNNING) { > raw_local_irq_disable(); > _local_bh_enable(); > raw_local_irq_enable(); > - > 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/ > - 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/ | ||||||||||
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