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Commit 9414232f authored by Ingo Molnar's avatar Ingo Molnar Committed by Linus Torvalds
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[PATCH] sched: fix cond_resched_softirq() offset 



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: default avatarIngo Molnar <mingo@elte.hu>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent d449db98

kernel/sched.c

+4 −14
Original line number Diff line number Diff line
@@ -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();