slab: Fix missing DEBUG_SLAB last user

Even with SLAB_RED_ZONE and SLAB_STORE_USER enabled, kernel would NOT store
redzone and last user data around allocated memory space if "arch cache line >
sizeof(unsigned long long)". As a result, last user information is unexpectedly
MISSED while dumping slab corruption log.

This fix makes sure that redzone and last user tags get stored unless the
required alignment breaks redzone's.

Signed-off-by: Shiyong Li <shi-yong.li@motorola.com>
Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>

1 files changed, 4 insertions, 4 deletions

diff --git a/mm/slab.c b/mm/slab.c
index bac0f4fcc216..525c66466469 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -2220,8 +2220,8 @@ kmem_cache_create (const char *name, size_t size, size_t align,
         if (ralign < align) {
                 ralign = align;
         }
-        /* disable debug if necessary */
-        if (ralign > __alignof__(unsigned long long))
+        /* disable debug if not aligning with REDZONE_ALIGN */
+        if (ralign & (__alignof__(unsigned long long) - 1))
                 flags &= ~(SLAB_RED_ZONE | SLAB_STORE_USER);
         /*
          * 4) Store it.
@@ -2247,8 +2247,8 @@ kmem_cache_create (const char *name, size_t size, size_t align,
          */
         if (flags & SLAB_RED_ZONE) {
                 /* add space for red zone words */
-                cachep->obj_offset += sizeof(unsigned long long);
-                size += 2 * sizeof(unsigned long long);
+                cachep->obj_offset += align;
+                size += align + sizeof(unsigned long long);
         }
         if (flags & SLAB_STORE_USER) {
                 /* user store requires one word storage behind the end of