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>

diff --git a/mm/slab.c b/mm/slab.c
index 8b71a9c3daa4a0b522451cbac2807f5fb3a424ba..21b2aef25254c191916e900b0913d03fa795b8bf 100644 (file)
--- 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);