linux-kernel - Re: x86-tip.today: flood of WARNING: at include/linux/sched.h:2238 run_posix_cpu

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Date:	Fri, 6 Feb 2009 15:01:34 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Mike Galbraith <efault@....de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Oleg Nesterov <oleg@...hat.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: x86-tip.today: flood of WARNING: at include/linux/sched.h:2238
	run_posix_cpu_timers+0xea/0x79f()


* Mike Galbraith <efault@....de> wrote:

> Greetings,
> 
> Futzing with kerneltop this morning, I fired up amarok to give it
> something light to monitor while I hunt missing events.  Something bad
> happened, and when I finally (SysRq-E took minutes) got control of box
> back, dmesg was full of a steady stream of the below.
> 
> That warning can be kinda unfriendly.
> 
> 
> [ 9964.600004] ------------[ cut here ]------------
> [ 9964.600006] WARNING: at include/linux/sched.h:2238 run_posix_cpu_timers+0xea/0x79f()

ah, that's Peter's stuff:

 4cd4c1b: timers: split process wide cpu clocks/timers
 32bd671: signal: re-add dead task accumulation stats.

The discussion with Oleg resulted in the conclusion i 
think that the warning is spurious and should be removed.

I've commited the minimal fix below to tip:master. There's
more fixes needed too but this should solve the warning
flood at least.

	Ingo

------------------------>
>From 7d8e23df69820e6be42bcc41d441f4860e8c76f7 Mon Sep 17 00:00:00 2001
From: Ingo Molnar <mingo@...e.hu>
Date: Fri, 6 Feb 2009 14:57:51 +0100
Subject: [PATCH] timers: split process wide cpu clocks/timers, remove spurious warning

Mike Galbraith reported that the new warning in thread_group_cputimer()
triggers en masse with Amarok running.

Oleg Nesterov observed:

  Can't fastpath_timer_check()->thread_group_cputimer() have the
  false warning too? Suppose we had the timer, then posix_cpu_timer_del()
  removes this timer, but task_cputime_zero(&sig->cputime_expires) still
  not true.

Remove the spurious debug warning.

Reported-by: Mike Galbraith <efault@....de>
Explained-by: Oleg Nesterov <oleg@...hat.com>
Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
 include/linux/sched.h |    2 --
 1 files changed, 0 insertions(+), 2 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 082d761..7939291 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2208,8 +2208,6 @@ void thread_group_cputimer(struct task_struct *tsk, struct task_cputime *times)
 	struct thread_group_cputimer *cputimer = &tsk->signal->cputimer;
 	unsigned long flags;
 
-	WARN_ON(!cputimer->running);
-
 	spin_lock_irqsave(&cputimer->lock, flags);
 	*times = cputimer->cputime;
 	spin_unlock_irqrestore(&cputimer->lock, flags);
--
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