mm: don't warn about large allocations for slab

Slub does not call kmalloc_slab() for sizes > KMALLOC_MAX_CACHE_SIZE,
instead it falls back to kmalloc_large().

For slab KMALLOC_MAX_CACHE_SIZE == KMALLOC_MAX_SIZE and it calls
kmalloc_slab() for all allocations relying on NULL return value for
over-sized allocations.

This inconsistency leads to unwanted warnings from kmalloc_slab() for
over-sized allocations for slab.  Returning NULL for failed allocations is
the expected behavior.

Make slub and slab code consistent by checking size >
KMALLOC_MAX_CACHE_SIZE in slab before calling kmalloc_slab().

While we are here also fix the check in kmalloc_slab().  We should check
against KMALLOC_MAX_CACHE_SIZE rather than KMALLOC_MAX_SIZE.  It all kinda
worked because for slab the constants are the same, and slub always checks
the size against KMALLOC_MAX_CACHE_SIZE before kmalloc_slab().  But if we
get there with size > KMALLOC_MAX_CACHE_SIZE anyhow bad things will
happen.  For example, in case of a newly introduced bug in slub code.

Also move the check in kmalloc_slab() from function entry to the size >
192 case.  This partially compensates for the additional check in slab
code and makes slub code a bit faster (at least theoretically).

Also drop __GFP_NOWARN in the warning check.  This warning means a bug in
slab code itself, user-passed flags have nothing to do with it.

Nothing of this affects slob.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Dmitry Vyukov <[email protected]>
Reported-by: [email protected]
Reported-by: [email protected]
Reported-by: [email protected]
Reported-by: [email protected]
Reported-by: [email protected]
Acked-by: Christoph Lameter <[email protected]>
Acked-by: Vlastimil Babka <[email protected]>
Cc: Pekka Enberg <[email protected]>
Cc: David Rientjes <[email protected]>
Cc: Joonsoo Kim <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

mm/slab.c

@@ -3675,6 +3675,8 @@ __do_kmalloc_node(size_t size, gfp_t flags, int node, unsigned long caller)
 	struct kmem_cache *cachep;
 	void *ret;
 
+	if (unlikely(size > KMALLOC_MAX_CACHE_SIZE))
+		return NULL;
 	cachep = kmalloc_slab(size, flags);
 	if (unlikely(ZERO_OR_NULL_PTR(cachep)))
 		return cachep;
@@ -3710,6 +3712,8 @@ static __always_inline void *__do_kmalloc(size_t size, gfp_t flags,
 	struct kmem_cache *cachep;
 	void *ret;
 
+	if (unlikely(size > KMALLOC_MAX_CACHE_SIZE))
+		return NULL;
 	cachep = kmalloc_slab(size, flags);
 	if (unlikely(ZERO_OR_NULL_PTR(cachep)))
 		return cachep;

mm/slab_common.c

@@ -1027,18 +1027,18 @@ struct kmem_cache *kmalloc_slab(size_t size, gfp_t flags)
 {
 	unsigned int index;
 
-	if (unlikely(size > KMALLOC_MAX_SIZE)) {
-		WARN_ON_ONCE(!(flags & __GFP_NOWARN));
-		return NULL;
-	}
-
 	if (size <= 192) {
 		if (!size)
 			return ZERO_SIZE_PTR;
 
 		index = size_index[size_index_elem(size)];
-	} else
+	} else {
+		if (unlikely(size > KMALLOC_MAX_CACHE_SIZE)) {
+			WARN_ON(1);
+			return NULL;
+		}
 		index = fls(size - 1);
+	}
 
 #ifdef CONFIG_ZONE_DMA
 	if (unlikely((flags & GFP_DMA)))