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Commit 6cb8f913 authored by Christoph Lameter's avatar Christoph Lameter Committed by Linus Torvalds
Browse files

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: default avatarChristoph Lameter <clameter@sgi.com>
Acked-by: default avatarPekka Enberg <penberg@cs.helsinki.fi>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent ef2ad80c

include/linux/slab.h

+13 −0
Original line number Diff line number Diff line
@@ -30,6 +30,19 @@ 
#define SLAB_MEM_SPREAD		0x00100000UL	/* Spread some memory over cpuset */

#define SLAB_TRACE		0x00200000UL	/* Trace allocations and frees */



/*

 * 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

 */

include/linux/slab_def.h

+12 −0
Original line number Diff line number Diff line
@@ -32,6 +32,10 @@ static inline void *kmalloc(size_t size, gfp_t flags) 
{

	if (__builtin_constant_p(size)) {

		int i = 0;



		if (!size)

			return ZERO_SIZE_PTR;



#define CACHE(x) \

		if (size <= x) \

			goto found; \
@@ -58,6 +62,10 @@ static inline void *kzalloc(size_t size, gfp_t flags) 
{

	if (__builtin_constant_p(size)) {

		int i = 0;



		if (!size)

			return ZERO_SIZE_PTR;



#define CACHE(x) \

		if (size <= x) \

			goto found; \
@@ -88,6 +96,10 @@ static inline void *kmalloc_node(size_t size, gfp_t flags, int node) 
{

	if (__builtin_constant_p(size)) {

		int i = 0;



		if (!size)

			return ZERO_SIZE_PTR;



#define CACHE(x) \

		if (size <= x) \

			goto found; \

include/linux/slub_def.h

+0 −12
Original line number Diff line number Diff line
@@ -159,18 +159,6 @@ 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)





void *kmem_cache_alloc(struct kmem_cache *, gfp_t);

void *__kmalloc(size_t size, gfp_t flags);

mm/slab.c

+8 −5
Original line number Diff line number Diff line
@@ -775,6 +775,9 @@ static inline struct kmem_cache *__find_general_cachep(size_t size, 
	 */

	BUG_ON(malloc_sizes[INDEX_AC].cs_cachep == NULL);

#endif

	if (!size)

		return ZERO_SIZE_PTR;



	while (size > csizep->cs_size)

		csizep++;
@@ -2351,7 +2354,7 @@ kmem_cache_create (const char *name, size_t size, size_t align, 
		 * 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;
@@ -3653,8 +3656,8 @@ __do_kmalloc_node(size_t size, gfp_t flags, int node, void *caller) 
	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);

}
@@ -3760,7 +3763,7 @@ 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);
@@ -4447,7 +4450,7 @@ 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));

mm/slob.c

+7 −4
Original line number Diff line number Diff line
@@ -347,7 +347,7 @@ static void slob_free(void *block, int size) 
	slobidx_t units;

	unsigned long flags;



	if (!block)

	if (ZERO_OR_NULL_PTR(block))

		return;

	BUG_ON(!size);
@@ -424,10 +424,13 @@ static void slob_free(void *block, int size) 


void *__kmalloc_node(size_t size, gfp_t gfp, int node)

{

	unsigned int *m;

	int align = max(ARCH_KMALLOC_MINALIGN, ARCH_SLAB_MINALIGN);



	if (size < PAGE_SIZE - align) {

		unsigned int *m;

		if (!size)

			return ZERO_SIZE_PTR;



		m = slob_alloc(size + align, gfp, align, node);

		if (m)

			*m = size;
@@ -450,7 +453,7 @@ 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);
@@ -468,7 +471,7 @@ 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);