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Subject[patch 03/26] Slab allocators: Consistent ZERO_SIZE_PTR support and NULL result semantics
Define ZERO_OR_NULL_PTR macro to be able to remove the checks
from the allocators. Move ZERO_SIZE_PTR related stuff into slab.h.

Make ZERO_SIZE_PTR work for all slab allocators and get rid of the
WARN_ON_ONCE(size == 0) that is still remaining in SLAB.

Make slub return NULL like the other allocators if a too large
memory segment is requested via __kmalloc.

Signed-off-by: Christoph Lameter <clameter@sgi.com>

---
include/linux/slab.h | 13 +++++++++++++
include/linux/slab_def.h | 12 ++++++++++++
include/linux/slub_def.h | 11 -----------
mm/slab.c | 14 ++++++++------
mm/slob.c | 13 ++++++++-----
mm/slub.c | 29 ++++++++++++++++-------------
mm/util.c | 2 +-
7 files changed, 58 insertions(+), 36 deletions(-)
Index: linux-2.6.22-rc4-mm2/include/linux/slab.h
===================================================================
--- linux-2.6.22-rc4-mm2.orig/include/linux/slab.h 2007-06-12 12:04:57.000000000 -0700
+++ linux-2.6.22-rc4-mm2/include/linux/slab.h 2007-06-17 20:35:03.000000000 -0700
@@ -33,6 +33,19 @@
#define SLAB_RECLAIM_ACCOUNT 0x00020000UL /* Objects are reclaimable */
#define SLAB_TEMPORARY SLAB_RECLAIM_ACCOUNT /* Objects are short-lived */
/*
+ * 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)
+
+#define ZERO_OR_NULL_PTR(x) ((unsigned long)(x) < \
+ (unsigned long)ZERO_SIZE_PTR)
+
+/*
* struct kmem_cache related prototypes
*/
void __init kmem_cache_init(void);
Index: linux-2.6.22-rc4-mm2/include/linux/slab_def.h
===================================================================
--- linux-2.6.22-rc4-mm2.orig/include/linux/slab_def.h 2007-06-04 17:57:25.000000000 -0700
+++ linux-2.6.22-rc4-mm2/include/linux/slab_def.h 2007-06-17 20:35:03.000000000 -0700
@@ -29,6 +29,10 @@ static inline void *kmalloc(size_t size,
{
if (__builtin_constant_p(size)) {
int i = 0;
+
+ if (!size)
+ return ZERO_SIZE_PTR;
+
#define CACHE(x) \
if (size <= x) \
goto found; \
@@ -55,6 +59,10 @@ static inline void *kzalloc(size_t size,
{
if (__builtin_constant_p(size)) {
int i = 0;
+
+ if (!size)
+ return ZERO_SIZE_PTR;
+
#define CACHE(x) \
if (size <= x) \
goto found; \
@@ -84,6 +92,10 @@ static inline void *kmalloc_node(size_t
{
if (__builtin_constant_p(size)) {
int i = 0;
+
+ if (!size)
+ return ZERO_SIZE_PTR;
+
#define CACHE(x) \
if (size <= x) \
goto found; \
Index: linux-2.6.22-rc4-mm2/include/linux/slub_def.h
===================================================================
--- linux-2.6.22-rc4-mm2.orig/include/linux/slub_def.h 2007-06-17 19:10:33.000000000 -0700
+++ linux-2.6.22-rc4-mm2/include/linux/slub_def.h 2007-06-17 20:35:03.000000000 -0700
@@ -160,17 +160,6 @@ static inline struct kmem_cache *kmalloc
#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)) {
Index: linux-2.6.22-rc4-mm2/mm/slab.c
===================================================================
--- linux-2.6.22-rc4-mm2.orig/mm/slab.c 2007-06-17 19:10:33.000000000 -0700
+++ linux-2.6.22-rc4-mm2/mm/slab.c 2007-06-17 20:35:08.000000000 -0700
@@ -774,7 +774,9 @@ static inline struct kmem_cache *__find_
*/
BUG_ON(malloc_sizes[INDEX_AC].cs_cachep == NULL);
#endif
- WARN_ON_ONCE(size == 0);
+ if (!size)
+ return ZERO_SIZE_PTR;
+
while (size > csizep->cs_size)
csizep++;

@@ -2340,7 +2342,7 @@ kmem_cache_create (const char *name, siz
* this should not happen at all.
* But leave a BUG_ON for some lucky dude.
*/
- BUG_ON(!cachep->slabp_cache);
+ BUG_ON(ZERO_OR_NULL_PTR(cachep->slabp_cache));
}
cachep->ctor = ctor;
cachep->name = name;
@@ -3642,8 +3644,8 @@ __do_kmalloc_node(size_t size, gfp_t fla
struct kmem_cache *cachep;

cachep = kmem_find_general_cachep(size, flags);
- if (unlikely(cachep == NULL))
- return NULL;
+ if (unlikely(ZERO_OR_NULL_PTR(cachep)))
+ return cachep;
return kmem_cache_alloc_node(cachep, flags, node);
}

@@ -3749,7 +3751,7 @@ void kfree(const void *objp)
struct kmem_cache *c;
unsigned long flags;

- if (unlikely(!objp))
+ if (unlikely(ZERO_OR_NULL_PTR(objp)))
return;
local_irq_save(flags);
kfree_debugcheck(objp);
@@ -4436,7 +4438,7 @@ const struct seq_operations slabstats_op
*/
size_t ksize(const void *objp)
{
- if (unlikely(objp == NULL))
+ if (unlikely(ZERO_OR_NULL_PTR(objp)))
return 0;

return obj_size(virt_to_cache(objp));
Index: linux-2.6.22-rc4-mm2/mm/slob.c
===================================================================
--- linux-2.6.22-rc4-mm2.orig/mm/slob.c 2007-06-17 19:10:33.000000000 -0700
+++ linux-2.6.22-rc4-mm2/mm/slob.c 2007-06-17 20:35:04.000000000 -0700
@@ -306,7 +306,7 @@ static void slob_free(void *block, int s
slobidx_t units;
unsigned long flags;

- if (!block)
+ if (ZERO_OR_NULL_PTR(block))
return;
BUG_ON(!size);

@@ -384,11 +384,14 @@ out:

void *__kmalloc(size_t size, gfp_t gfp)
{
+ unsigned int *m;
int align = max(ARCH_KMALLOC_MINALIGN, ARCH_SLAB_MINALIGN);

if (size < PAGE_SIZE - align) {
- unsigned int *m;
- m = slob_alloc(size + align, gfp, align);
+ if (!size)
+ return ZERO_SIZE_PTR;
+
+ m = slob_alloc(size + align, gfp, align);
if (m)
*m = size;
return (void *)m + align;
@@ -411,7 +414,7 @@ void kfree(const void *block)
{
struct slob_page *sp;

- if (!block)
+ if (ZERO_OR_NULL_PTR(block))
return;

sp = (struct slob_page *)virt_to_page(block);
@@ -430,7 +433,7 @@ size_t ksize(const void *block)
{
struct slob_page *sp;

- if (!block)
+ if (ZERO_OR_NULL_PTR(block))
return 0;

sp = (struct slob_page *)virt_to_page(block);
Index: linux-2.6.22-rc4-mm2/mm/util.c
===================================================================
--- linux-2.6.22-rc4-mm2.orig/mm/util.c 2007-06-17 19:10:33.000000000 -0700
+++ linux-2.6.22-rc4-mm2/mm/util.c 2007-06-17 20:35:03.000000000 -0700
@@ -99,7 +99,7 @@ void *krealloc(const void *p, size_t new

if (unlikely(!new_size)) {
kfree(p);
- return NULL;
+ return ZERO_SIZE_PTR;
}

ks = ksize(p);
Index: linux-2.6.22-rc4-mm2/mm/slub.c
===================================================================
--- linux-2.6.22-rc4-mm2.orig/mm/slub.c 2007-06-17 19:10:33.000000000 -0700
+++ linux-2.6.22-rc4-mm2/mm/slub.c 2007-06-17 20:35:04.000000000 -0700
@@ -2279,10 +2279,11 @@ static struct kmem_cache *get_slab(size_
int index = kmalloc_index(size);

if (!index)
- return NULL;
+ return ZERO_SIZE_PTR;

/* Allocation too large? */
- BUG_ON(index < 0);
+ if (index < 0)
+ return NULL;

#ifdef CONFIG_ZONE_DMA
if ((flags & SLUB_DMA)) {
@@ -2323,9 +2324,10 @@ void *__kmalloc(size_t size, gfp_t flags
{
struct kmem_cache *s = get_slab(size, flags);

- if (s)
- return slab_alloc(s, flags, -1, __builtin_return_address(0));
- return ZERO_SIZE_PTR;
+ if (ZERO_OR_NULL_PTR(s))
+ return s;
+
+ return slab_alloc(s, flags, -1, __builtin_return_address(0));
}
EXPORT_SYMBOL(__kmalloc);

@@ -2334,9 +2336,10 @@ void *__kmalloc_node(size_t size, gfp_t
{
struct kmem_cache *s = get_slab(size, flags);

- if (s)
- return slab_alloc(s, flags, node, __builtin_return_address(0));
- return ZERO_SIZE_PTR;
+ if (ZERO_OR_NULL_PTR(s))
+ return s;
+
+ return slab_alloc(s, flags, node, __builtin_return_address(0));
}
EXPORT_SYMBOL(__kmalloc_node);
#endif
@@ -2387,7 +2390,7 @@ void kfree(const void *x)
* this comparison would be true for all "negative" pointers
* (which would cover the whole upper half of the address space).
*/
- if ((unsigned long)x <= (unsigned long)ZERO_SIZE_PTR)
+ if (ZERO_OR_NULL_PTR(x))
return;

page = virt_to_head_page(x);
@@ -2706,8 +2709,8 @@ void *__kmalloc_track_caller(size_t size
{
struct kmem_cache *s = get_slab(size, gfpflags);

- if (!s)
- return ZERO_SIZE_PTR;
+ if (ZERO_OR_NULL_PTR(s))
+ return s;

return slab_alloc(s, gfpflags, -1, caller);
}
@@ -2717,8 +2720,8 @@ void *__kmalloc_node_track_caller(size_t
{
struct kmem_cache *s = get_slab(size, gfpflags);

- if (!s)
- return ZERO_SIZE_PTR;
+ if (ZERO_OR_NULL_PTR(s))
+ return s;

return slab_alloc(s, gfpflags, node, caller);
}
--
-
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