From: Vlastimil Babka vbabka@suse.cz
commit 0882ff9190e3bc51e2d78c3aadd7c690eeaa91d5 upstream.
In SLUB, prefetch_freepointer() is used when allocating an object from cache's freelist, to make sure the next object in the list is cache-hot, since it's probable it will be allocated soon.
Commit 2482ddec670f ("mm: add SLUB free list pointer obfuscation") has unintentionally changed the prefetch in a way where the prefetch is turned to a real fetch, and only the next->next pointer is prefetched. In case there is not a stream of allocations that would benefit from prefetching, the extra real fetch might add a useless cache miss to the allocation. Restore the previous behavior.
Link: http://lkml.kernel.org/r/20180809085245.22448-1-vbabka@suse.cz Fixes: 2482ddec670f ("mm: add SLUB free list pointer obfuscation") Signed-off-by: Vlastimil Babka vbabka@suse.cz Acked-by: Kees Cook keescook@chromium.org Cc: Daniel Micay danielmicay@gmail.com Cc: Eric Dumazet edumazet@google.com 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 Cc: Matthias Schiffer mschiffer@universe-factory.net Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Sven Eckelmann sven@narfation.org Signed-off-by: Sasha Levin sashal@kernel.org --- mm/slub.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-)
diff --git a/mm/slub.c b/mm/slub.c index 3c1a16f03b2bd..481518c3f61a9 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -269,8 +269,7 @@ static inline void *get_freepointer(struct kmem_cache *s, void *object)
static void prefetch_freepointer(const struct kmem_cache *s, void *object) { - if (object) - prefetch(freelist_dereference(s, object + s->offset)); + prefetch(object + s->offset); }
static inline void *get_freepointer_safe(struct kmem_cache *s, void *object)