Date: Sun, 17 Apr 2016 08:00:55 -0400
From: Michal Hocko <mhocko@kernel.org>
To: Tejun Heo <tj@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>, Petr Mladek <pmladek@suse.com>,
        cgroups@vger.kernel.org, Cyril Hrubis <chrubis@suse.cz>,
        linux-kernel@vger.kernel.org
Subject: Re: [BUG] cgroup/workques/fork: deadlock when moving cgroups
Message-ID: <20160417120053.GB21757@dhcp22.suse.cz>
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On Fri 15-04-16 11:25:26, Tejun Heo wrote:
> Hello,

Hi,

> On Fri, Apr 15, 2016 at 05:08:15PM +0200, Michal Hocko wrote:
[...]
> > Well it certainly is not that trivial because it relies on being
> > exclusive with global context. I will have to look closer of course but
> > I cannot guarantee I will get to it before I get back from LSF. We can
> > certainly discuss that at the conference. Johannes will be there as
> > well.
> 
> I see.  For cpuset, it didn't really matter but what we can do is
> creating a mechanism on cgroup core side which is called after a
> migration operation is done after dropping the usual locks and
> guarantees that no new migration will be started before the callbacks
> finish.  If we have that, relocating charge moving outside the attach
> path should be pretty trivial, right?

Yeah, I guess this should work as well. I would have to double check the
code, I cannot say it would be my favorite so I might have forgot some
subtle details.
-- 
Michal Hocko
SUSE Labs