linux-kernel - Re: [PATCH 1/7] containers (V7): Generic container system abstracted from cpusets code

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Message-ID: <6599ad830702121126o35fb0cb6x696a4a56079bce40@mail.gmail.com>
Date:	Mon, 12 Feb 2007 11:26:34 -0800
From:	"Paul Menage" <menage@...gle.com>
To:	vatsa@...ibm.com
Cc:	akpm@...l.org, pj@....com, sekharan@...ibm.com, dev@...ru,
	xemul@...ru, serue@...ibm.com, ebiederm@...ssion.com,
	ckrm-tech@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
	rohitseth@...gle.com, mbligh@...gle.com, winget@...gle.com,
	containers@...ts.osdl.org, devel@...nvz.org
Subject: Re: [PATCH 1/7] containers (V7): Generic container system abstracted from cpusets code

On 2/12/07, Srivatsa Vaddagiri <vatsa@...ibm.com> wrote:
> On Mon, Feb 12, 2007 at 12:15:22AM -0800, menage@...gle.com wrote:
> > +void container_fork(struct task_struct *child)
> > +{
> > +     task_lock(current);
>
> Can't this be just rcu_read_lock()?
>

In this particular patch (which is an almost verbatim
extraction/renaming of the generic bits of the cpusets code into
container.c) it probably could - but the main patch that adds the
container_group support would lose it since we use kref to refcount
container_group objects, and hence they're freed when their refcount
reaches zero. RCU is still fine for reading the container_group
pointers, but it's no good for updating them, since by the time you
update it it may no longer be your container_group structure, and may
instead be about to be deleted as soon as the other thread's
rcu_synchronize() completes.

Paul
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