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Subject[15/15] slub: fix a possible memleak in __slab_alloc()
3.0-stable review patch.  If anyone has any objections, please let me know.


From: Eric Dumazet <>

commit 73736e0387ba0e6d2b703407b4d26168d31516a7 upstream.

Zhihua Che reported a possible memleak in slub allocator on

It is possible current thread migrates right before disabling irqs in
__slab_alloc(). We must check again c->freelist, and perform a normal
allocation instead of scratching c->freelist.

Many thanks to Zhihua Che for spotting this bug, introduced in 2.6.39

V2: Its also possible an IRQ freed one (or several) object(s) and
populated c->freelist, so its not a CONFIG_PREEMPT only problem.

Reported-by: Zhihua Che <>
Signed-off-by: Eric Dumazet <>
Acked-by: Christoph Lameter <>
Signed-off-by: Pekka Enberg <>
Signed-off-by: Greg Kroah-Hartman <>

mm/slub.c | 6 ++++++
1 file changed, 6 insertions(+)

--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1818,6 +1818,11 @@ static void *__slab_alloc(struct kmem_ca
if (unlikely(!node_match(c, node)))
goto another_slab;

+ /* must check again c->freelist in case of cpu migration or IRQ */
+ object = c->freelist;
+ if (object)
+ goto update_freelist;
stat(s, ALLOC_REFILL);

@@ -1827,6 +1832,7 @@ load_freelist:
if (kmem_cache_debug(s))
goto debug;

c->freelist = get_freepointer(s, object);
page->inuse = page->objects;
page->freelist = NULL;

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