linux-kernel - Re: [PATCH] slub: Hold list_lock unconditionally before the call to add

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Date:	Sat, 8 Feb 2014 08:30:56 +0530
From:	Gautham R Shenoy <ego@...ux.vnet.ibm.com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Gautham R Shenoy <ego@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org, peterz@...radead.org,
	penberg@...nel.org
Subject: Re: [PATCH] slub: Hold list_lock unconditionally before the call to
 add_full.

On Fri, Feb 07, 2014 at 12:46:19PM -0800, David Rientjes wrote:
> On Sat, 8 Feb 2014, Gautham R Shenoy wrote:
> 
> > Hi,
> > 
> > From the lockdep annotation and the comment that existed before the
> > lockdep annotations were introduced, 
> > mm/slub.c:add_full(s, n, page) expects to be called with n->list_lock
> > held.
> > 
> > However, there's a call path in deactivate_slab() when
> > 
> > 	 (new.inuse || n->nr_partial <= s->min_partial) &&
> > 	 !(new.freelist) &&
> >          !(kmem_cache_debug(s))
> > 
> > which ends up calling add_full() without holding
> > n->list_lock.
> > 
> > This was discovered while onlining/offlining cpus in 3.14-rc1 due to
> > the lockdep annotations added by commit
> > c65c1877bd6826ce0d9713d76e30a7bed8e49f38.
> > 
> > Fix this by unconditionally taking the lock
> > irrespective of the state of kmem_cache_debug(s).
> > 
> > Cc: Peter Zijlstra <peterz@...radead.org>
> > Cc: Pekka Enberg <penberg@...nel.org>
> > Signed-off-by: Gautham R. Shenoy <ego@...ux.vnet.ibm.com>
> 
> No, it's not needed unless kmem_cache_debug(s) is actually set, 
> specifically s->flags & SLAB_STORE_USER.
> 
> You want the patch at http://marc.info/?l=linux-kernel&m=139147105027693 
> instead which is already in -mm and linux-next.
>

Ah, thanks! Wasn't aware of this fix. Shall apply this one.

--
Thanks and Regards
gautham. 

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