[PATCH] slab: ensure cache_alloc_refill terminates

[Pekka J Enberg <penberg@cs.helsinki.fi>]

From: Pekka Enberg <penberg@cs.helsinki.fi>

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 patch adds a BUG_ON for the case where a slab in partial or free
list has no available objects for allocation to ensure
cache_alloc_refill terminates.

Cc: Michael Richardson <mcr@sandelman.ca>
Cc: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>
---
 mm/slab.c |    8 ++++++++
 1 file changed, 8 insertions(+)

Index: 2.6/mm/slab.c
===================================================================
--- 2.6.orig/mm/slab.c	2007-02-19 09:58:28.000000000 +0200
+++ 2.6/mm/slab.c	2007-02-19 10:19:20.000000000 +0200
@@ -2987,6 +2987,14 @@
 		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 >= cachep->num);
+
 		while (slabp->inuse < cachep->num && batchcount--) {
 			STATS_INC_ALLOCED(cachep);
 			STATS_INC_ACTIVE(cachep);
-
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