* OGAWA Hirofumi <[email protected]> wrote:
> "Fabio Comolli" <[email protected]> writes:
>
> > Just found this in syslog. It was during normal activity, about 6
> > minutes after resume-from-ram. I never saw this before.
>
> It seems someone missed to check PREEMPT_ACTIVE in __resched_legal().
but PREEMPT_ACTIVE is 0x10000000, not 0x20000000.
> Could you please test the following patch?
no. cond_resched() is always legal in the !PREEMPT case.
i found another bug and realized that the whole __resched_legal()
approach is fundamentally wrong! The patch below fixes this.
Ingo
------------------->
Subject: [patch] sched: remove __resched_legal() and fix cond_resched_softirq()
From: Ingo Molnar <[email protected]>
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.
But __resched_legal() hid this fact. Same goes for cond_resched_locked()
and cond_resched_softirq().
furthermore, the __legal_resched(0) call was buggy in
cond_resched_softirq() and caused unnecessary long softirq latencies!
the fix is to preserve the only valid inhibitor to voluntary preemption:
if the system is still booting. None of the other behavior of
__resched_legal() made any sense.
the effect of this fix should be more real bugs exposed, and shorter
softirq latencies.
Signed-off-by: Ingo Molnar <[email protected]>
---
kernel/sched.c | 17 +++--------------
1 file changed, 3 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 +4636,7 @@ static void __cond_resched(void)
int __sched cond_resched(void)
{
- if (need_resched() && __resched_legal(0)) {
+ if (need_resched() && system_state == SYSTEM_RUNNING) {
__cond_resched();
return 1;
}
@@ -4673,7 +4662,7 @@ 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 +4678,7 @@ 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 [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Stuff]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
[Linux Resources]
