Messages in this thread Patch in this message | | | From | Vlastimil Babka <> | Subject | [PATCH] mm, slub: restore the original intention of prefetch_freepointer() | Date | Thu, 9 Aug 2018 10:52:45 +0200 |
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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.
Signed-off-by: Vlastimil Babka <vbabka@suse.cz> Cc: 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> --- While I don't expect this to be causing the bug at hand, it's worth fixing. For the bug it might mean that the page fault moves elsewhere.
mm/slub.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-)
diff --git a/mm/slub.c b/mm/slub.c index 51258eff4178..ce2b9e5cea77 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -271,8 +271,7 @@ 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) -- 2.18.0
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