linux-kernel - Re: [Bug #12465] KVM guests stalling on 2.6.28 (bisected)

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Date:	Tue, 20 Jan 2009 17:19:36 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Kevin Shanahan <kmshanah@...b.org.au>, Avi Kivity <avi@...hat.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Kernel Testers List <kernel-testers@...r.kernel.org>,
	Mike Galbraith <efault@....de>,
	bugme-daemon@...zilla.kernel.org
Subject: Re: [Bug #12465] KVM guests stalling on 2.6.28 (bisected)

On Tue, 2009-01-20 at 17:06 +0100, Ingo Molnar wrote:
> se.wait_max                        :           -92.027877
> 
> that field is not supposed to be negative. Mike, Peter, any ideas?

Possibly unrelated, but whilst I was poking at try_to_wake_up yesterday,
I thought I spotted a site where we fail to update rq clock.

Since we just moved the task to a new cpu (and thus rq) we need to
update_rq_clock() again.

diff --git a/kernel/sched.c b/kernel/sched.c
index d7ae5f4..6cd5e52 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -2398,6 +2398,7 @@ static int try_to_wake_up(struct task_struct *p, unsigned int state, int sync)
 	if (cpu != orig_cpu) {
 		set_task_cpu(p, cpu);
 		task_rq_unlock(rq, &flags);
+		update_rq_clock(rq);
 		/* might preempt at this point */
 		rq = task_rq_lock(p, &flags);
 		old_state = p->state;


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