From mboxrd@z Thu Jan  1 00:00:00 1970
From: Yong Zhang <yong.zhang0@gmail.com>
Subject: Re: [PATCH -rt] memcg: use migrate_disable()/migrate_enable( ) in
 memcg_check_events()
Date: Thu, 17 Nov 2011 11:03:32 +0800
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Reply-To: Yong Zhang <yong.zhang0@gmail.com>
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Cc: Steven Rostedt <rostedt@goodmis.org>,
	LKML <linux-kernel@vger.kernel.org>,
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	Peter Zijlstra <peterz@infradead.org>
To: Thomas Gleixner <tglx@linutronix.de>
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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.

Works for me.

Thanks,
Yong