slub: do not merge cache if slub_debug contains a never-merge flag

In case CONFIG_SLUB_DEBUG_ON=n, find_mergeable() gets debug features from
commandline but never checks if there are features from the
SLAB_NEVER_MERGE set.

As a result selected by slub_debug caches are always mergeable if they
have been created without a custom constructor set or without one of the
SLAB_* debug features on.

This moves the SLAB_NEVER_MERGE check below the flags update from
commandline to make sure it won't merge the slab cache if one of the debug
features is on.

Link: http://lkml.kernel.org/r/20170101124451.GA4740@lp-laptop-d
Signed-off-by: Grygorii Maistrenko <grygoriimkd@gmail.com>
Reviewed-by: Pekka Enberg <penberg@kernel.org>
Acked-by: David Rientjes <rientjes@google.com>
Acked-by: Christoph Lameter <cl@linux.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/slab_common.c b/mm/slab_common.c
index ae32384..36a263e 100644 (file)
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -255,7 +255,7 @@ struct kmem_cache *find_mergeable(size_t size, size_t align,
 {
        struct kmem_cache *s;
 
-       if (slab_nomerge || (flags & SLAB_NEVER_MERGE))
+       if (slab_nomerge)
                return NULL;
 
        if (ctor)
@@ -266,6 +266,9 @@ struct kmem_cache *find_mergeable(size_t size, size_t align,
        size = ALIGN(size, align);
        flags = kmem_cache_flags(size, flags, name, NULL);
 
+       if (flags & SLAB_NEVER_MERGE)
+               return NULL;
+
        list_for_each_entry_reverse(s, &slab_caches, list) {
                if (slab_unmergeable(s))
                        continue;