Date: Sun, 19 Dec 2010 03:03:13 +0100
From: Miklos Vajna <vmiklos@frugalware.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: shenghui <crosslonelyover@gmail.com>, kernel-janitors@vger.kernel.org,
        linux-kernel@vger.kernel.org, mingo@elte.hu, Greg KH <greg@kroah.com>
Subject: Re: [PATCH] avoid race condition in pick_next_task_fair in
 kernel/sched_fair.c
Message-ID: <20101219020313.GJ31750@genesis.frugalware.org>
References: <AANLkTin49UHeVhfS-iFwWvPIg29HPhXaP3DorBAa-a0I@mail.gmail.com>
 <1277808215.1868.5.camel@laptop>
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On Tue, Jun 29, 2010 at 12:43:35PM +0200, Peter Zijlstra <peterz@infradead.=
org> wrote:
> On Tue, 2010-06-29 at 15:10 +0800, shenghui wrote:
> > I think some lock on the metadata can fix this issue, but we may
> > change plenty of code to add support for lock. I think the easist
> > way is just substacting nr_running before dequing tasks.=20
>=20
> But all that is fully serialized by the rq->lock.. so I'm really not
> seeing how this can happen.

Hi,

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?

Thanks,

Miklos

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