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authorChristoph Lameter <clameter@sgi.com>2007-06-08 13:46:49 -0700
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2007-06-08 17:23:33 -0700
commit272c1d21d6fe42979068e14c04fb60fb6045ad74 (patch)
tree6a365c67ed8575d15a59aa2183df609368359724 /include/linux
parenta17627ef8833ac30622a7b39b7be390e1b174405 (diff)
SLUB: return ZERO_SIZE_PTR for kmalloc(0)
Instead of returning the smallest available object return ZERO_SIZE_PTR. A ZERO_SIZE_PTR can be legitimately used as an object pointer as long as it is not deferenced. The dereference of ZERO_SIZE_PTR causes a distinctive fault. kfree can handle a ZERO_SIZE_PTR in the same way as NULL. This enables functions to use zero sized object. e.g. n = number of objects. objects = kmalloc(n * sizeof(object)); for (i = 0; i < n; i++) objects[i].x = y; kfree(objects); Signed-off-by: Christoph Lameter <clameter@sgi.com> Acked-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>
Diffstat (limited to 'include/linux')
-rw-r--r--include/linux/slub_def.h25
1 files changed, 17 insertions, 8 deletions
diff --git a/include/linux/slub_def.h b/include/linux/slub_def.h
index 0764c829d967..a0ad37463d62 100644
--- a/include/linux/slub_def.h
+++ b/include/linux/slub_def.h
@@ -70,11 +70,8 @@ extern struct kmem_cache kmalloc_caches[KMALLOC_SHIFT_HIGH + 1];
*/
static inline int kmalloc_index(size_t size)
{
- /*
- * We should return 0 if size == 0 but we use the smallest object
- * here for SLAB legacy reasons.
- */
- WARN_ON_ONCE(size == 0);
+ if (!size)
+ return 0;
if (size > KMALLOC_MAX_SIZE)
return -1;
@@ -153,13 +150,25 @@ static inline struct kmem_cache *kmalloc_slab(size_t size)
#define SLUB_DMA 0
#endif
+
+/*
+ * ZERO_SIZE_PTR will be returned for zero sized kmalloc requests.
+ *
+ * Dereferencing ZERO_SIZE_PTR will lead to a distinct access fault.
+ *
+ * ZERO_SIZE_PTR can be passed to kfree though in the same way that NULL can.
+ * Both make kfree a no-op.
+ */
+#define ZERO_SIZE_PTR ((void *)16)
+
+
static inline void *kmalloc(size_t size, gfp_t flags)
{
if (__builtin_constant_p(size) && !(flags & SLUB_DMA)) {
struct kmem_cache *s = kmalloc_slab(size);
if (!s)
- return NULL;
+ return ZERO_SIZE_PTR;
return kmem_cache_alloc(s, flags);
} else
@@ -172,7 +181,7 @@ static inline void *kzalloc(size_t size, gfp_t flags)
struct kmem_cache *s = kmalloc_slab(size);
if (!s)
- return NULL;
+ return ZERO_SIZE_PTR;
return kmem_cache_zalloc(s, flags);
} else
@@ -188,7 +197,7 @@ static inline void *kmalloc_node(size_t size, gfp_t flags, int node)
struct kmem_cache *s = kmalloc_slab(size);
if (!s)
- return NULL;
+ return ZERO_SIZE_PTR;
return kmem_cache_alloc_node(s, flags, node);
} else