Re: + mm-memcg-lockdep-annotation-for-memcg-oom-lock.patch added to -mm tree

[Johannes Weiner <hannes@cmpxchg.org>]

On Thu, Oct 31, 2013 at 09:50:17AM +0100, Michal Hocko wrote:
> On Wed 30-10-13 15:12:48, Andrew Morton wrote:
> > Subject: + mm-memcg-lockdep-annotation-for-memcg-oom-lock.patch added to -mm tree
> > To: hannes@cmpxchg.org,mhocko@suse.cz
> > From: akpm@linux-foundation.org
> > Date: Wed, 30 Oct 2013 15:12:48 -0700
> > 
> > 
> > The patch titled
> >      Subject: mm: memcg: lockdep annotation for memcg OOM lock
> > has been added to the -mm tree.  Its filename is
> >      mm-memcg-lockdep-annotation-for-memcg-oom-lock.patch
> > 
> > This patch should soon appear at
> >     http://ozlabs.org/~akpm/mmots/broken-out/mm-memcg-lockdep-annotation-for-memcg-oom-lock.patch
> > and later at
> >     http://ozlabs.org/~akpm/mmotm/broken-out/mm-memcg-lockdep-annotation-for-memcg-oom-lock.patch
> > 
> > Before you just go and hit "reply", please:
> >    a) Consider who else should be cc'ed
> >    b) Prefer to cc a suitable mailing list as well
> >    c) Ideally: find the original patch on the mailing list and do a
> >       reply-to-all to that, adding suitable additional cc's
> > 
> > *** Remember to use Documentation/SubmitChecklist when testing your code ***
> > 
> > The -mm tree is included into linux-next and is updated
> > there every 3-4 working days
> > 
> > ------------------------------------------------------
> > From: Johannes Weiner <hannes@cmpxchg.org>
> > Subject: mm: memcg: lockdep annotation for memcg OOM lock
> > 
> > The memcg OOM lock is a mutex-type lock that is open-coded due to memcg's
> > special needs.  Add annotations for lockdep coverage.
> 
> I am not sure what this gives us to be honest. AA and AB-BA deadlocks
> are impossible due to nature of the lock (it is trylock so we never
> block on it).

It's not an actual trylock, because we loop around it.  If it fails,
we wait for the unlock, restart the fault, and try again.  That's a
LOCK operation.

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