linux-kernel - Re: [PATCH] slub: Fix sysfs circular locking dependency

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Message-ID: <AANLkTin6N2s1RN6PBX=f0v69Ny-NkEKk_iAgqscuYgMM@mail.gmail.com>
Date:	Sat, 8 Jan 2011 08:42:42 +0100
From:	Bart Van Assche <bvanassche@....org>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Christoph Lameter <cl@...ux.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Pekka Enberg <penberg@...nel.org>,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] slub: Fix sysfs circular locking dependency

On Fri, Jan 7, 2011 at 9:34 PM, David Rientjes <rientjes@...gle.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@...ux.com>
>
> Acked-by: David Rientjes <rientjes@...gle.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@...nel.org be CC-ed too ?

Bart.
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