slub: fix a possible memleak in __slab_alloc()

Zhihua Che reported a possible memleak in slub allocator on
CONFIG_PREEMPT=y builds.

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.

Cc: <[email protected]>        [2.6.39+]
Reported-by: Zhihua Che <[email protected]>
Signed-off-by: Eric Dumazet <[email protected]>
Acked-by: Christoph Lameter <[email protected]>
Signed-off-by: Pekka Enberg <[email protected]>

diff --git a/mm/slub.c b/mm/slub.c
index 108ed03fb422673619de978f5db6a4384107fe24..5e410a95abaf02674d36c3d969f01ecee332bfac 100644 (file)
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2169,6 +2169,11 @@ redo:
                goto new_slab;
        }
 
+       /* must check again c->freelist in case of cpu migration or IRQ */
+       object = c->freelist;
+       if (object)
+               goto load_freelist;
+
        stat(s, ALLOC_SLOWPATH);
 
        do {