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SubjectRe: [PATCH tip/core/urgent] rcu: protect fork-time cgroup access
On Mon, Mar 29, 2010 at 11:42:55PM +0200, Peter Zijlstra wrote:
> 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 :-)

No argument here! ;-)

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

K, adding them to CC. The two splats are:

http://pastebin.ubuntu.com/406131/
http://paste.ubuntu.com/406189/

Some additional RCU protection is required, or perhaps some suppression
of false positives. Thoughts?

> 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 :/

Sigh!

Thanx, Paul


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