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Subject: Re: [PATCH] slub: Fix sysfs circular locking dependency
From: Pekka Enberg <penberg@kernel.org>
To: Bart Van Assche <bvanassche@acm.org>
Cc: David Rientjes <rientjes@google.com>, Christoph Lameter <cl@linux.com>,
        KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
        linux-kernel@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>
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Date: Sat, 08 Jan 2011 10:28:43 +0200
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On Sat, 2011-01-08 at 08:42 +0100, Bart Van Assche wrote:
> On Fri, Jan 7, 2011 at 9:34 PM, David Rientjes <rientjes@google.com> wrote:
> >
> > On Fri, 7 Jan 2011, Christoph Lameter wrote:
> >
> > > Subject: slub: Avoid use of slub_lock in show_slab_objects()
> > >
> > > The purpose of the locking is to prevent removal and additions
> > > of nodes when statistics are gathered for a slab cache. So we
> > > need to avoid racing with memory hotplug functionality.
> > >
> > > It is enough to take the memory hotplug locks there instead
> > > of the slub_lock.
> > >
> >
> > Because memory hotplug is the only time s->node[] is modified after the
> > sysfs files are created, which is the only time show_slab_objects() is
> > called.
> >
> > > online_pages() does not acquire the memory_hotplug lock. So
> > > add the missing locking there.
> > >
> > > Signed-off-by: Christoph Lameter <cl@linux.com>
> >
> > Acked-by: David Rientjes <rientjes@google.com>
> >
> >  [ Should probably be seperated out into two patches, one for the
> >   memory hotplug locking addition and one for the slub fix, both
> >   should be pushed during this merge window.  If so, a comment
> >   describing the new semantics of lock_memory_hotplug() to protect
> >   data structures that may be modified in hotplug notifier
> >   callbacks would be appreciated. ]
> 
> Shouldn't stable@kernel.org be CC-ed too ?

Yup, I'll add it to the patch.