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* sched: only update rq->clock while holding rq->lock
@ 2008-10-15 18:37 Peter Zijlstra
  2008-10-16  2:32 ` Srivatsa Vaddagiri
  0 siblings, 1 reply; 3+ messages in thread
From: Peter Zijlstra @ 2008-10-15 18:37 UTC (permalink / raw)
  To: Ingo Molnar; +Cc: vatsa, linux-kernel, Dhaval Giani, Balbir Singh

Vatsa,

you said someone would send a patch to this effect, I don't want to
steal credit, but I think this patch is better posted sooner rather than
later.

---

Subject: sched: only update rq->clock while holding rq->lock
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
Date: Wed Oct 15 20:30:26 CEST 2008

Vatsa noticed rq->clock going funny and tracked it down to an update_rq_clock()
outside a rq->lock section.

This is a problem because things like double_rq_lock() update the rq->clock
value for both rqs. Therefore disabling interrupts isn't strong enough.

Reported-by: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
---
 kernel/sched.c |    6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

Index: linux-2.6/kernel/sched.c
===================================================================
--- linux-2.6.orig/kernel/sched.c
+++ linux-2.6/kernel/sched.c
@@ -4448,12 +4448,8 @@ need_resched_nonpreemptible:
 	if (sched_feat(HRTICK))
 		hrtick_clear(rq);
 
-	/*
-	 * Do the rq-clock update outside the rq lock:
-	 */
-	local_irq_disable();
+	spin_lock_irq(&rq->lock);
 	update_rq_clock(rq);
-	spin_lock(&rq->lock);
 	clear_tsk_need_resched(prev);
 
 	if (prev->state && !(preempt_count() & PREEMPT_ACTIVE)) {



^ permalink raw reply	[flat|nested] 3+ messages in thread

* Re: sched: only update rq->clock while holding rq->lock
  2008-10-15 18:37 sched: only update rq->clock while holding rq->lock Peter Zijlstra
@ 2008-10-16  2:32 ` Srivatsa Vaddagiri
  2008-10-16  8:29   ` Peter Zijlstra
  0 siblings, 1 reply; 3+ messages in thread
From: Srivatsa Vaddagiri @ 2008-10-16  2:32 UTC (permalink / raw)
  To: Peter Zijlstra
  Cc: Ingo Molnar, linux-kernel, Dhaval Giani, Balbir Singh, shaggy, brking

On Wed, Oct 15, 2008 at 08:37:23PM +0200, Peter Zijlstra wrote:
> Vatsa noticed rq->clock going funny and tracked it down to an update_rq_clock()
> outside a rq->lock section.

For the records, actually Brian King and David Kleikamp noticed this!

-- 
Regards,
vatsa

^ permalink raw reply	[flat|nested] 3+ messages in thread

* Re: sched: only update rq->clock while holding rq->lock
  2008-10-16  2:32 ` Srivatsa Vaddagiri
@ 2008-10-16  8:29   ` Peter Zijlstra
  0 siblings, 0 replies; 3+ messages in thread
From: Peter Zijlstra @ 2008-10-16  8:29 UTC (permalink / raw)
  To: vatsa
  Cc: Ingo Molnar, linux-kernel, Dhaval Giani, Balbir Singh, shaggy, brking

On Thu, 2008-10-16 at 08:02 +0530, Srivatsa Vaddagiri wrote:
> On Wed, Oct 15, 2008 at 08:37:23PM +0200, Peter Zijlstra wrote:
> > Vatsa noticed rq->clock going funny and tracked it down to an update_rq_clock()
> > outside a rq->lock section.
> 
> For the records, actually Brian King and David Kleikamp noticed this!

Thanks Brian and Shaggy!



^ permalink raw reply	[flat|nested] 3+ messages in thread

end of thread, other threads:[~2008-10-16  8:30 UTC | newest]

Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2008-10-15 18:37 sched: only update rq->clock while holding rq->lock Peter Zijlstra
2008-10-16  2:32 ` Srivatsa Vaddagiri
2008-10-16  8:29   ` Peter Zijlstra

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