linux-kernel - Re: [PATCH RFC] perf_counter: Don't swap contexts containing locked mutex

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Date:	Fri, 29 May 2009 16:49:21 +0300
From:	Pekka Enberg <penberg@...helsinki.fi>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Mike Galbraith <efault@....de>,
	Paul Mackerras <paulus@...ba.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC] perf_counter: Don't swap contexts containing
 locked mutex

Hi Ingo,

On Fri, 2009-05-29 at 14:35 +0200, Ingo Molnar wrote:
> * Ingo Molnar <mingo@...e.hu> wrote:
> 
> > try the latest Git repo (i tried 95110d7) and do this:
> > 
> >   make clean
> >   perf stat -- make -j
> > 
> > that locks up for me, very quickly, with permanently stuck tasks:
> > 
> >    PID USER      PR  NI  VIRT  RES  SHR S  %CPU %MEM   TIME    COMMAND        
> >  10748 mingo     20   0     0    0    0 R 100.4  0.0   0:06.44 chmod         
> >  10756 mingo     20   0     0    0    0 R 100.4  0.0   0:06.43 touch         
> > 
> > looping in the remove-context retry loop.
> 
> ok, after muchos debugging and tracing this turned out to be the 
> perf_counter_task_exit() in kernel/fork.c, in the fork() failure 
> path. That zapped the task ctx in cpuctx and caused the next 
> schedule (which is rare) to not schedule the real context out. Then, 
> when the task was scheduled back in again later, we scheduled in 
> already active counters. Much mayhem followed and the lockup was a 
> common incarnation of that. I pushed out a couple of fixes for this.
> 
> Pekka, the symptoms appear to match your 'stuck Xorg while make -j' 
> symptoms pretty accurately - so if you try latest perfcounters/core 
> it might solve some of those problems as well.

Yup, works much better here. Thanks!

Tested-by: Pekka Enberg <penberg@...helsinki.fi>

			Pekka

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