slab: Ignore internal flags in cache creation

Some flags are used internally by the allocators for management
purposes. One example of that is the CFLGS_OFF_SLAB flag that slab uses
to mark that the metadata for that cache is stored outside of the slab.

No cache should ever pass those as a creation flags. We can just ignore
this bit if it happens to be passed (such as when duplicating a cache in
the kmem memcg patches).

Because such flags can vary from allocator to allocator, we allow them
to make their own decisions on that, defining SLAB_AVAILABLE_FLAGS with
all flags that are valid at creation time.  Allocators that doesn't have
any specific flag requirement should define that to mean all flags.

Common code will mask out all flags not belonging to that set.

Acked-by: Christoph Lameter <cl@linux.com>
Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: Glauber Costa <glommer@parallels.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>

1 files changed, 7 insertions, 0 deletions

diff --git a/mm/slab_common.c b/mm/slab_common.c
index 5fb753da6cf0..b705be7faa48 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -109,6 +109,13 @@ struct kmem_cache *kmem_cache_create(const char *name, size_t size, size_t align
 	if (!kmem_cache_sanity_check(name, size) == 0)
 		goto out_locked;
 
+	/*
+	 * Some allocators will constraint the set of valid flags to a subset
+	 * of all flags. We expect them to define CACHE_CREATE_MASK in this
+	 * case, and we'll just provide them with a sanitized version of the
+	 * passed flags.
+	 */
+	flags &= CACHE_CREATE_MASK;
 
 	s = __kmem_cache_alias(name, size, align, flags, ctor);
 	if (s)