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

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Message-ID: <alpine.DEB.2.00.1101061239520.30820@chino.kir.corp.google.com>
Date:	Thu, 6 Jan 2011 12:47:08 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Christoph Lameter <cl@...ux.com>
cc:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Pekka Enberg <penberg@...nel.org>,
	Bart Van Assche <bvanassche@....org>,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] slub: Fix sysfs circular locking dependency

On Thu, 6 Jan 2011, Christoph Lameter wrote:

> slab_mem_going_online_callback() etc already take the slub_lock since they
> have to iterate over the list of slab caches in existence. We could take
> the hotplug lock there as well.
> 
> Kame-san: Can you enlighten us on hotplug locking? And also check this
> patch?
> 

Yeah, I was going to suggest doing the lock_memory_hotplug() before taking 
slub_lock in the callback, but I really think it should be done in 
online_pages().  Since the offline case is already handled, this would 
expand the semantics of lock_memory_hotplug() to serialize the access of 
data structures that can change in a memory hotplug notifier callback 
without locking at the lower level.
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