linux-kernel - Re: [PATCH tip/core/urgent] rcu: protect fork-time cgroup access

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Message-ID: <1269898975.12097.380.camel@laptop>
Date:	Mon, 29 Mar 2010 23:42:55 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	paulmck@...ux.vnet.ibm.com
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org,
	mathieu.desnoyers@...ymtl.ca, josh@...htriplett.org,
	dvhltc@...ibm.com, niv@...ibm.com, tglx@...utronix.de,
	rostedt@...dmis.org, Valdis.Kletnieks@...edu, dhowells@...hat.com,
	eric.dumazet@...il.com, abogani@...ware.it
Subject: Re: [PATCH tip/core/urgent] rcu: protect fork-time cgroup access

On Mon, 2010-03-29 at 14:34 -0700, Paul E. McKenney wrote:

> And it appears that my patch is at best insufficient:
> http://paste.ubuntu.com/406189/
> 
> Left to myself, I would wrap copy_process() with rcu_read_lock(),
> but I would rather hear your thoughts before doing too much more
> semi-random hacking.  ;-)

Well, I don't think you can get away with that, copy_process() wants to
sleep on quite a few places ;-) Also, locks should be taken at the
smallest possible scope, unless we want to go back to BKL style
locking :-)

As to that freezer splat, you'd have to chase down the cgroup folks, I'm
fully ignorant on that.

For the set_task_rq() one, I'm afraid someone (which again I'm afraid
will be me) will have to look into how the task_group muck ties into the
cgroup muck as I think the original authors of that ran off :/



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