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

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Message-ID: <20111201192935.GE13173@google.com>
Date:	Thu, 1 Dec 2011 11:29:35 -0800
From:	Tejun Heo <tj@...nel.org>
To:	Linus Torvalds <torvalds@...ux-foundation.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 UPDATED 03/10] threadgroup: extend threadgroup_lock()
 to cover exit and exec

Hello again, Linus.

On Sun, Nov 27, 2011 at 01:25:58PM -0800, Tejun Heo wrote:
> The problem is that cred_guard_mutex uses _interruptible/_killable
> operations and rwsem doesn't have them, so cred_guard_mutex can't be
> easily replaced with write-locking group_rwsem.
> 
> If the two locks can't be merged, under the proposed scheme, while not
> exactly pretty, both fork/exit and exec paths go through single
> locking and only the ones which want stable threadgroup need to grab
> both locks, so IMHO it is at least reasonable.
> 
> Any better ideas?

I agree that the proposed solution is rather ugly but stable
thread-group is a valid mechanism to have and cgroup can benefit a lot
from it.  I'd be happy to revamp the implementation if anyone can come
up with a better way and can add big fat comment stating that.  Until
something better comes up, would it be okay to stick with this
implementation?

Thanks.

-- 
tejun
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