linux-kernel - Re: [PATCH 3/4] threadgroup: extend threadgroup

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Message-ID: <20110913075444.GE11397@mtj.dyndns.org>
Date:	Tue, 13 Sep 2011 16:54:44 +0900
From:	Tejun Heo <htejun@...il.com>
To:	Paul Menage <paul@...lmenage.org>
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,
	Oleg Nesterov <oleg@...hat.com>,
	Paul Menage <menage@...gle.com>
Subject: Re: [PATCH 3/4] threadgroup: extend threadgroup_lock() to cover exit
 and exec

On Sun, Sep 11, 2011 at 09:04:55PM -0700, Paul Menage wrote:
> On Sun, Sep 4, 2011 at 11:01 AM, Tejun Heo <htejun@...il.com> wrote:
> > From: Tejun Heo <tj@...nel.org>
> >
> > threadgroup_lock() protected only protected against new addition to
> > the threadgroup, which was inherently somewhat incomplete and
> > problematic for its only user cgroup.  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 patch extends threadgroup_lock() such that it protects against
> > all three threadgroup altering operations - fork, exit and exec.  For
> > exit, threadgroup_change_begin/end() calls are added to exit path.
> > For exec, threadgroup_[un]lock() are updated to also grab and release
> > cred_guard_mutex.
> 
> Can you add a comment (either in the commit or in the code) about why
> the cred_guard_mutex change is necessary? Is it simply that exec takes
> cred_guard_mutex and hence this excludes exec, or is there something
> more subtle?

Will do so.  It's just for the exclusion of cred_guard_mutex.  Maybe
we better rename it to exec_mutex or something, I don't know.

Thanks.

-- 
tejun
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