Re: [PATCH -rt] memcg: use migrate_disable()/migrate_enable( ) in memcg_check_events()

On Wed, 16 Nov 2011 17:18:09 +0000
Luis Henriques [off-list ref] wrote:

On Wed, Nov 16, 2011 at 06:02:42PM +0100, Thomas Gleixner wrote:

quoted

On Wed, 16 Nov 2011, Steven Rostedt wrote:

quoted

On Wed, 2011-11-16 at 17:16 +0800, Yong Zhang wrote:

quoted

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,

Could you CC the final patch to cgroups@vger.kernel.org ?
Does this fix will go thorugh rt tree rather than -mm ?

Thanks,
-Kame