linux-kernel - Re: [PATCH -rt] memcg: use migrate_disable()/migrate_enable( ) in memcg_check

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Message-ID: <20111116171809.GA1999@hades>
Date:	Wed, 16 Nov 2011 17:18:09 +0000
From:	Luis Henriques <henrix@...andro.org>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Yong Zhang <yong.zhang0@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-rt-users <linux-rt-users@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH -rt] memcg: use migrate_disable()/migrate_enable( ) in
 memcg_check_events()

On Wed, Nov 16, 2011 at 06:02:42PM +0100, Thomas Gleixner wrote:
> On Wed, 16 Nov 2011, Steven Rostedt wrote:
> > On Wed, 2011-11-16 at 17:16 +0800, Yong Zhang wrote:
> > > Looking at commit 4799401f [memcg: Fix race condition in
> > > memcg_check_events() with this_cpu usage], we just want
> > > to disable migration. So use the right API in -rt. This
> > > will cure below warning.
> > No this won't work. Not even for -rt. If we disable migration but not
> > preemption, then two tasks can take this path. And the checks in
> > __memcg_event_check() will be corrupted because nothing is protecting
> > the updates from two tasks going into the same path.
> > 
> > Perhaps a local_lock would work.
> 
> Yes, that's the only sensible option for now. Untested patch below.

I run a quick test and it looks like the problem is gone.

Cheers,
--
Luis Henriques
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