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, 8 insertions, 5 deletions

diff --git a/mm/slab.c b/mm/slab.c
index 4bd8a53091b7..d2cd304fd8af 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -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));