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

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Message-ID: <20111123143444.GA14549@somewhere.redhat.com>
Date:	Wed, 23 Nov 2011 15:34:53 +0100
From:	Frederic Weisbecker <fweisbec@...il.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, 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 Mon, Nov 21, 2011 at 02:03:26PM -0800, Tejun Heo wrote:
> On Mon, Nov 14, 2011 at 02:54:08PM +0100, Frederic Weisbecker wrote:
> > > Also note this is currently protected by the tasklist readlock. Cred guard mutex is
> > > certainly better, I just don't remember if you remove the tasklist lock in a
> > > further patch.
> > 
> > Ah recalling what Ben Blum said, we also need the leader to stay stable because it
> > is excpected to be passed in ->can_attach(), ->attach(), ->cancel_attach(), ...
> > Although that's going to change after your patches that pass a flex array.
> 
> Not really without locking out exec.  The thing is whoever is exec'ing
> will be the leader and we can't guarantee that the first in the flex
> array is always the leader.  One method may see it as the leader, the
> next one might not.

Exactly!
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