Re: [PATCH] slub: Fix sysfs circular locking dependency

From: Christoph Lameter
Date: Thu Jan 06 2011 - 13:11:09 EST

On Thu, 6 Jan 2011, David Rientjes wrote:

> > Thanks for testing. David, does Christoph's patch look OK to you?
> >
> I think it certainly fixes the problem at hand, but I think we also need
> to do lock_memory_hotplug() for memory hotplug in
> slab_mem_going_online_callback() to make show_slab_objects() consistent
> when being printed during concurrent node hot-add since it sets bits in
> N_NORMAL_MEMORY. The MEM_OFFLINE callback is already handled at a higher
> level by taking the lock in the hotplug layer, but we need to protect the
> MEM_GOING_ONLINE and MEM_CANCEL_ONLINE callbacks if slub_lock is no longer
> used to protect node arrays (which was admittedly always convenient since
> it's typically associated with an iteration through slab_caches).

Hmm, I would have expected the callbacks all to be done under hotplug

The MEM_GOING_ONLINE callback is not that critical since a node that is
coming online presumably has only a minimal set of objects necessary for
potential future allocations.

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

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