diff options
| author | Christoph Lameter <clameter@sgi.com> | 2007-06-08 13:46:49 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@woody.linux-foundation.org> | 2007-06-08 17:23:33 -0700 |
| commit | 272c1d21d6fe42979068e14c04fb60fb6045ad74 (patch) | |
| tree | 6a365c67ed8575d15a59aa2183df609368359724 /include/linux | |
| parent | a17627ef8833ac30622a7b39b7be390e1b174405 (diff) | |
| download | blackbird-op-linux-272c1d21d6fe42979068e14c04fb60fb6045ad74.tar.gz blackbird-op-linux-272c1d21d6fe42979068e14c04fb60fb6045ad74.zip | |
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.h | 25 |
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 |
