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>
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>

1 files changed, 16 insertions, 13 deletions

diff --git a/mm/slub.c b/mm/slub.c
index 1b0a95d..548d78d 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2270,10 +2270,11 @@ static struct kmem_cache *get_slab(size_t size, gfp_t flags)
 	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)) {
@@ -2314,9 +2315,10 @@ 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);
 
@@ -2325,9 +2327,10 @@ void *__kmalloc_node(size_t size, gfp_t flags, int node)
 {
 	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
@@ -2378,7 +2381,7 @@ 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);
@@ -2687,8 +2690,8 @@ void *__kmalloc_track_caller(size_t size, gfp_t gfpflags, void *caller)
 {
 	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);
 }
@@ -2698,8 +2701,8 @@ void *__kmalloc_node_track_caller(size_t size, gfp_t gfpflags,
 {
 	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);
 }