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[PATCH] sched: fix cond_resched_softirq() offset

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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>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Ingo Molnar 2006-12-29 16:48:13 -08:00 committed by Linus Torvalds
parent d449db98d5
commit 9414232fa0
1 changed files with 4 additions and 14 deletions
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18
kernel/sched.c
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@ -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();