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Date: Mon, 12 Dec 2011 09:17:47 +0200 (EET)
From: Pekka Enberg <penberg@...nel.org>
To: Christoph Lameter <cl@...ux.com>
cc: David Rientjes <rientjes@...gle.com>,
Eric Dumazet <eric.dumazet@...il.com>,
linux-kernel@...r.kernel.org
Subject: Re: slub: Lockout validation scans during freeing of object
On Wed, 23 Nov 2011, Christoph Lameter wrote:
> Eric tested this one.
>
>
> Subject: slub: Lockout validation scans during freeing of object
>
> Slab validation can run right now while the slab free paths prepare
> the redzone fields etc around the objects in preparation of the
> actual freeing of the object. This can lead to false positives.
>
> Take the node lock unconditionally during free so that the validation
> can examine objects without them being disturbed by freeing operations.
>
> Signed-off-by: Christoph Lameter <cl@...ux.com>
>
> ---
> mm/slub.c | 12 ++++++++++--
> 1 file changed, 10 insertions(+), 2 deletions(-)
>
> Index: linux-2.6/mm/slub.c
> ===================================================================
> --- linux-2.6.orig/mm/slub.c 2011-11-22 10:42:19.000000000 -0600
> +++ linux-2.6/mm/slub.c 2011-11-22 10:44:34.000000000 -0600
> @@ -2391,8 +2391,15 @@ static void __slab_free(struct kmem_cach
>
> stat(s, FREE_SLOWPATH);
>
> - if (kmem_cache_debug(s) && !free_debug_processing(s, page, x, addr))
> - return;
> + if (kmem_cache_debug(s)) {
> +
> + /* Lock out any concurrent validate_slab calls */
> + n = get_node(s, page_to_nid(page));
> + spin_lock_irqsave(&n->list_lock, flags);
> +
> + if (!free_debug_processing(s, page, x, addr))
> + goto out;
> + }
>
> do {
> prior = page->freelist;
> @@ -2471,6 +2478,7 @@ static void __slab_free(struct kmem_cach
> stat(s, FREE_ADD_PARTIAL);
> }
> }
> +out:
> spin_unlock_irqrestore(&n->list_lock, flags);
> return;
Ditto.
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