linux-kernel - Re: [PATCHSET cgroup] extend threadgroup locking

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Date:	Sun, 11 Sep 2011 21:11:16 -0700
From:	Paul Menage <paul@...lmenage.org>
To:	Tejun Heo <htejun@...il.com>
Cc:	rjw@...k.pl, lizf@...fujitsu.com,
	linux-pm@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
	containers@...ts.linux-foundation.org, fweisbec@...il.com,
	matthltc@...ibm.com, akpm@...ux-foundation.org
Subject: Re: [PATCHSET cgroup] extend threadgroup locking

On Sun, Sep 4, 2011 at 11:01 AM, Tejun Heo <htejun@...il.com> wrote:
> Hello,
>
> cgroup currently only blocks new threads from joining the target
> threadgroup during migration, and on-going migration could race
> against exec and exit leading to interesting problems - the symmetry
> between various attach methods, task exiting during method execution,
> ->exit() racing against attach methods, migrating task switching basic
> properties during exec and so on.
>
> This patchset extends threadgroup locking such that it covers all
> operations which can alter the threadgroup - fork, exit and exec, and
> update cgroup to take advantage of it.  rwsem read ops are added to
> exit path but exec is excluded by grabbing the existing
> cred_guard_mutex from threadgroup locking helper.
>
> This makes threadgroup locking complete and resolves cgroup issues
> stemming from the target taskset being unstable.
>
> This patchset is on top of the current pm-freezer + "freezer: fixes &
> simplifications" patchset and contains the following four patches.
> Patch list and diffstat follow.
>
> Thanks.
>
>  [PATCH 1/4] cgroup: change locking order in attach_task_by_pid()
>  [PATCH 2/4] threadgroup: rename signal->threadgroup_fork_lock to
>  [PATCH 3/4] threadgroup: extend threadgroup_lock() to cover exit and
>  [PATCH 4/4] cgroup: always lock threadgroup during migration
>

Looks like a nice cleanup from the cgroups point of view. Hopefully
Oleg or other folks who have a handle on the performance impact of the
changes in the exit/exec code are happy with it.

Acked-by: Paul Menage <paul@...lmenage.org>

Thanks,
Paul
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