[patch 1/3] mm, slub: restore initial kmem_cache flags

[Andrew Morton <akpm@linux-foundation.org>]

From: Eric Farman <farman@linux.ibm.com>
Subject: mm, slub: restore initial kmem_cache flags

The routine that applies debug flags to the kmem_cache slabs inadvertantly
prevents non-debug flags from being applied to those same objects.  That
is, if slub_debug=<flag>,<slab> is specified, non-debugged slabs will end
up having flags of zero, and the slabs may be unusable.

Fix this by including the input flags for non-matching slabs with the
contents of slub_debug, so that the caches are created as expected
alongside any debugging options that may be requested.  With this, we can
remove the check for a NULL slub_debug_string, since it's covered by the
loop itself.

Link: https://lkml.kernel.org/r/20200930161931.28575-1-farman@linux.ibm.com
Fixes: e17f1dfba37b ("mm, slub: extend slub_debug syntax for multiple blocks")
Signed-off-by: Eric Farman <farman@linux.ibm.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Kees Cook <keescook@chromium.org>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/slub.c |    6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

--- a/mm/slub.c~mm-slub-restore-initial-kmem_cache-flags
+++ a/mm/slub.c
@@ -1413,10 +1413,6 @@ slab_flags_t kmem_cache_flags(unsigned i
 	char *next_block;
 	slab_flags_t block_flags;
 
-	/* If slub_debug = 0, it folds into the if conditional. */
-	if (!slub_debug_string)
-		return flags | slub_debug;
-
 	len = strlen(name);
 	next_block = slub_debug_string;
 	/* Go through all blocks of debug options, see if any matches our slab's name */
@@ -1450,7 +1446,7 @@ slab_flags_t kmem_cache_flags(unsigned i
 		}
 	}
 
-	return slub_debug;
+	return flags | slub_debug;
 }
 #else /* !CONFIG_SLUB_DEBUG */
 static inline void setup_object_debug(struct kmem_cache *s,
_