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>

7 files changed, 57 insertions, 35 deletions

diff --git a/include/linux/slab.h b/include/linux/slab.h
index 27402fea9b79..0289ec89300a 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -31,6 +31,19 @@
 #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
  */
 void __init kmem_cache_init(void);
diff --git a/include/linux/slab_def.h b/include/linux/slab_def.h
index 365d036c454a..16e814ffab8d 100644
--- a/include/linux/slab_def.h
+++ b/include/linux/slab_def.h
@@ -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; \
diff --git a/include/linux/slub_def.h b/include/linux/slub_def.h
index a582f6771525..579b0a22858e 100644
--- a/include/linux/slub_def.h
+++ b/include/linux/slub_def.h
@@ -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);
 
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));
diff --git a/mm/slob.c b/mm/slob.c
index 154e7bdf3544..41d32c3c0be4 100644
--- a/mm/slob.c
+++ b/mm/slob.c
@@ -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 @@ out:
 
 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);
diff --git a/mm/slub.c b/mm/slub.c
index 1b0a95d75dbb..548d78df81e1 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);
 }
diff --git a/mm/util.c b/mm/util.c
index 18396ea63ee6..f2f21b775516 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -76,7 +76,7 @@ void *krealloc(const void *p, size_t new_size, gfp_t flags)
 
         if (unlikely(!new_size)) {
                 kfree(p);
-                return NULL;
+                return ZERO_SIZE_PTR;
         }
 
         ks = ksize(p);