linux-kernel - Re: [BUG?] 2.6.25-rc[23]-mm1 cgroup list corruption under load with VM Scalability patches

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Date:	Wed, 5 Mar 2008 13:09:13 -0800
From:	"Paul Menage" <menage@...gle.com>
To:	"Lee Schermerhorn" <Lee.Schermerhorn@...com>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Rik van Riel" <riel@...hat.com>
Subject: Re: [BUG?] 2.6.25-rc[23]-mm1 cgroup list corruption under load with VM Scalability patches

On Wed, Mar 5, 2008 at 11:37 AM, Lee Schermerhorn
<Lee.Schermerhorn@...com> wrote:
> list_del corruption in cgroup_exit() on 16 cpu, 32GB ia64 NUMA platform.
>
>  I've been seeing this for a while now, but we've had known problems
>  [page leaks, ...] with the VM scalability series.  Now the system
>  appears to be running very well with these patches under stress loads
>  that would hang it or cause OOM kill of tests with plenty of swap space
>  left.  Eventually, [after 40-45 minutes], I hit a list corruption in
>  cgroup_exit().
>
>  I can't say for sure that our patches aren't causing this, but I've been
>  unable to keep the system up long enough under the stress load w/o the
>  splitlru+noreclaim patches to hit the problem.
>
>  I looked in the mailing lists and found one other thread related to
>  cgroup list corruption:
>
>         http://marc.info/?l=linux-kernel&m=119263666823236&w=4
>
>  Paul looked into this and couldn't see anywhere that the lists are
>  manipulate w/o holding the css set lock.  I concur.  I did find one
>  possible race in enabling the task cg_lists [see patch below], but this
>  did not solve the problem.  And I did not hit the printk in the patch.

No, that's not a (malign) race - cgroup_enable_task_cg_lists() is
idempotent. In the case that you see, every thread seen in the
do_each_thread() loop will already have a non-empty cg_list field, so
it will be a no-op. So adding the additional check isn't wrong but
it's not needed.

I'll look again at the code to try to figure out where the problem is.

Paul
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