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

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Message-ID: <AANLkTinft80dXqE-U=YDB23d9=BgXLCxJzgiA_gF4cVL@mail.gmail.com>
Date:	Wed, 5 Jan 2011 20:26:08 +0200
From:	Pekka Enberg <penberg@...nel.org>
To:	Christoph Lameter <cl@...ux.com>
Cc:	David Rientjes <rientjes@...gle.com>, linux-kernel@...r.kernel.org,
	Bart Van Assche <bart.vanassche@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] slub: Fix sysfs circular locking dependency

On Wed, Jan 5, 2011 at 7:10 PM, Christoph Lameter <cl@...ux.com> wrote:
> How about this solution? In the common case of kernels without hotplug
> support there will be no locking at all.
>
>
> 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.
>
>
> Signed-off-by: Christoph Lameter <cl@...ux.com>
>
> ---
>  mm/slub.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> Index: linux-2.6/mm/slub.c
> ===================================================================
> --- linux-2.6.orig/mm/slub.c    2011-01-05 09:55:34.000000000 -0600
> +++ linux-2.6/mm/slub.c 2011-01-05 09:56:27.000000000 -0600
> @@ -3821,7 +3821,7 @@ static ssize_t show_slab_objects(struct
>                }
>        }
>
> -       down_read(&slub_lock);
> +       lock_memory_hotplug();
>  #ifdef CONFIG_SLUB_DEBUG
>        if (flags & SO_ALL) {
>                for_each_node_state(node, N_NORMAL_MEMORY) {
> @@ -3862,7 +3862,7 @@ static ssize_t show_slab_objects(struct
>                        x += sprintf(buf + x, " N%d=%lu",
>                                        node, nodes[node]);
>  #endif
> -       up_read(&slub_lock);
> +       unlock_memory_hotplug();
>        kfree(nodes);
>        return x + sprintf(buf + x, "\n");
>  }

Makes sense. Bart, does this fix the problem for you?
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