linux-kernel - Re: [PATCH 03/10] threadgroup: extend threadgroup

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Message-Id: <20111104174534.8950f403.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Fri, 4 Nov 2011 17:45:34 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	paul@...lmenage.org, 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@...hat.com,
	kamezawa.hiroyu@...fujitsu.com
Subject: Re: [PATCH 03/10] threadgroup: extend threadgroup_lock() to cover
 exit and exec

On Tue,  1 Nov 2011 16:46:26 -0700
Tejun Heo <tj@...nel.org> wrote:

> 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.
> 
> With this change, threadgroup_lock() guarantees that the target
> threadgroup will remain stable - no new task will be added, no new
> PF_EXITING will be set and exec won't happen.
> 
> The next patch will update cgroup so that it can take full advantage
> of this change.
> 
> Signed-off-by: Tejun Heo <tj@...nel.org>
> Cc: Oleg Nesterov <oleg@...hat.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Paul Menage <paul@...lmenage.org>
> Cc: Li Zefan <lizf@...fujitsu.com>


Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>

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