linux-kernel - Re: [PATCH] avoid race condition in pick_next_task_fair in kernel/sched

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Message-ID: <20101222002248.GP10557@genesis.frugalware.org>
Date:	Wed, 22 Dec 2010 01:22:48 +0100
From:	Miklos Vajna <vmiklos@...galware.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	shenghui <crosslonelyover@...il.com>,
	kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org,
	mingo@...e.hu, Greg KH <greg@...ah.com>,
	systemd-devel@...ts.freedesktop.org
Subject: Re: [PATCH] avoid race condition in pick_next_task_fair in
 kernel/sched_fair.c

On Sun, Dec 19, 2010 at 03:03:13AM +0100, Miklos Vajna <vmiklos@...galware.org> wrote:
> Here is a panic I got today:
> 
> http://frugalware.org/~vmiklos/pics/bug/2.6.37-rc6.png
> 
> More details:
> 
> I get this sometimes on boot or shutdown when testing systemd. I did not
> get it with sysvinit, so I guess it may be related to systemd's heavy
> cgroups usage, but I'm not sure. Sadly it isn't 100% reproducible but I
> usually hit it at least once a day.
> 
> The config is here:
> http://frugalware.org/~vmiklos/logs/2.6.37-rc6.config (I just did a
> yes "" | make config to update it to 2.6.37-rc6.)
> 
> I got something similar with 2.6.36.1 as well:
> 
> http://frugalware.org/~vmiklos/pics/bug/2.6.36.1.png
> 
> Ah, and this is on i686 in VMware - though given that I never had this
> problem with systemd, I guess it won't be an emulator bug. :)
> 
> I'm not familiar with the sched code, is it possible that this is
> related?

A few more info:

- I reproduced the issue on my Lenovo S12 netbook as well, so it's not a
  virtual machine-related bug. Here is a poor shot:
  http://frugalware.org/~vmiklos/pics/bug/p1040730.jpg
- I'm also attaching the full dmesg in the VM that is finally a text
  using serial console.
- On "how to reproduce": sometimes I just get this during boot. If it
  does not occur, then it does when using "systemctl emergency".

Please let me know if you need more info.

Thanks,

Miklos

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