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

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Message-ID: <20101219020313.GJ31750@genesis.frugalware.org>
Date:	Sun, 19 Dec 2010 03:03:13 +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>
Subject: Re: [PATCH] avoid race condition in pick_next_task_fair in
 kernel/sched_fair.c

On Tue, Jun 29, 2010 at 12:43:35PM +0200, Peter Zijlstra <peterz@...radead.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. 
> 
> 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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