mm/slab: move kmalloc_slab() to mm/slab.h

In preparation for the next patch, move the kmalloc_slab() function to
the header, as it will have callers from two files, and make it inline.
To avoid unnecessary bloat, remove all size checks/warnings from
kmalloc_slab() as they just duplicate those in callers, especially after
recent changes to kmalloc_size_roundup(). We just need to adjust handling
of zero size in __do_kmalloc_node(). Also we can stop handling NULL
result from kmalloc_slab() there as that now cannot happen (unless
called too early during boot).

The size_index array becomes visible so rename it to a more specific
kmalloc_size_index.
Reviewed-by: Kees Cook <keescook@chromium.org>
Acked-by: David Rientjes <rientjes@google.com>
Tested-by: David Rientjes <rientjes@google.com>
Reviewed-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Tested-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>

mm/slab.h

@@ -389,8 +389,32 @@ extern const struct kmalloc_info_struct {
 void setup_kmalloc_cache_index_table(void);
 void create_kmalloc_caches(slab_flags_t);
 
-/* Find the kmalloc slab corresponding for a certain size */
-struct kmem_cache *kmalloc_slab(size_t size, gfp_t flags, unsigned long caller);
+extern u8 kmalloc_size_index[24];
+
+static inline unsigned int size_index_elem(unsigned int bytes)
+{
+	return (bytes - 1) / 8;
+}
+
+/*
+ * Find the kmem_cache structure that serves a given size of
+ * allocation
+ *
+ * This assumes size is larger than zero and not larger than
+ * KMALLOC_MAX_CACHE_SIZE and the caller must check that.
+ */
+static inline struct kmem_cache *
+kmalloc_slab(size_t size, gfp_t flags, unsigned long caller)
+{
+	unsigned int index;
+
+	if (size <= 192)
+		index = kmalloc_size_index[size_index_elem(size)];
+	else
+		index = fls(size - 1);
+
+	return kmalloc_caches[kmalloc_type(flags, caller)][index];
+}
 
 void *__kmem_cache_alloc_node(struct kmem_cache *s, gfp_t gfpflags,
 			      int node, size_t orig_size,

mm/slab_common.c

@@ -665,7 +665,7 @@ EXPORT_SYMBOL(random_kmalloc_seed);
  * of two cache sizes there. The size of larger slabs can be determined using
  * fls.
  */
-static u8 size_index[24] __ro_after_init = {
+u8 kmalloc_size_index[24] __ro_after_init = {
 	3,	/* 8 */
 	4,	/* 16 */
 	5,	/* 24 */
@@ -692,33 +692,6 @@ static u8 size_index[24] __ro_after_init = {
 	2	/* 192 */
 };
 
-static inline unsigned int size_index_elem(unsigned int bytes)
-{
-	return (bytes - 1) / 8;
-}
-
-/*
- * Find the kmem_cache structure that serves a given size of
- * allocation
- */
-struct kmem_cache *kmalloc_slab(size_t size, gfp_t flags, unsigned long caller)
-{
-	unsigned int index;
-
-	if (size <= 192) {
-		if (!size)
-			return ZERO_SIZE_PTR;
-
-		index = size_index[size_index_elem(size)];
-	} else {
-		if (WARN_ON_ONCE(size > KMALLOC_MAX_CACHE_SIZE))
-			return NULL;
-		index = fls(size - 1);
-	}
-
-	return kmalloc_caches[kmalloc_type(flags, caller)][index];
-}
-
 size_t kmalloc_size_roundup(size_t size)
 {
 	if (size && size <= KMALLOC_MAX_CACHE_SIZE) {
@@ -843,9 +816,9 @@ void __init setup_kmalloc_cache_index_table(void)
 	for (i = 8; i < KMALLOC_MIN_SIZE; i += 8) {
 		unsigned int elem = size_index_elem(i);
 
-		if (elem >= ARRAY_SIZE(size_index))
+		if (elem >= ARRAY_SIZE(kmalloc_size_index))
 			break;
-		size_index[elem] = KMALLOC_SHIFT_LOW;
+		kmalloc_size_index[elem] = KMALLOC_SHIFT_LOW;
 	}
 
 	if (KMALLOC_MIN_SIZE >= 64) {
@@ -854,7 +827,7 @@ void __init setup_kmalloc_cache_index_table(void)
 		 * is 64 byte.
 		 */
 		for (i = 64 + 8; i <= 96; i += 8)
-			size_index[size_index_elem(i)] = 7;
+			kmalloc_size_index[size_index_elem(i)] = 7;
 
 	}
 
@@ -865,7 +838,7 @@ void __init setup_kmalloc_cache_index_table(void)
 		 * instead.
 		 */
 		for (i = 128 + 8; i <= 192; i += 8)
-			size_index[size_index_elem(i)] = 8;
+			kmalloc_size_index[size_index_elem(i)] = 8;
 	}
 }
 
@@ -977,10 +950,10 @@ void *__do_kmalloc_node(size_t size, gfp_t flags, int node, unsigned long caller
 		return ret;
 	}
 
-	s = kmalloc_slab(size, flags, caller);
+	if (unlikely(!size))
+		return ZERO_SIZE_PTR;
 
-	if (unlikely(ZERO_OR_NULL_PTR(s)))
-		return s;
+	s = kmalloc_slab(size, flags, caller);
 
 	ret = __kmem_cache_alloc_node(s, flags, node, size, caller);
 	ret = kasan_kmalloc(s, ret, size, flags);