slab: ensure cache_alloc_refill terminates

If slab->inuse is corrupted, cache_alloc_refill can enter an infinite
loop as detailed by Michael Richardson in the following post:
<http://lkml.org/lkml/2007/2/16/292>. This adds a BUG_ON to catch
those cases.

Cc: Michael Richardson <mcr@sandelman.ca>
Acked-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 8 insertions, 0 deletions

diff --git a/mm/slab.c b/mm/slab.c
index 8b71a9c3daa4..21b2aef25254 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -2990,6 +2990,14 @@ retry:
                 slabp = list_entry(entry, struct slab, list);
                 check_slabp(cachep, slabp);
                 check_spinlock_acquired(cachep);
+
+                /*
+                 * The slab was either on partial or free list so
+                 * there must be at least one object available for
+                 * allocation.
+                 */
+                BUG_ON(slabp->inuse < 0 || slabp->inuse >= cachep->num);
+
                 while (slabp->inuse < cachep->num && batchcount--) {
                         STATS_INC_ALLOCED(cachep);
                         STATS_INC_ACTIVE(cachep);