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Date:   Fri,  1 May 2020 15:20:59 +0200
From:   Greg Kroah-Hartman <>
Cc:     Greg Kroah-Hartman <>,, Vlastimil Babka <>,
        Kees Cook <>,
        Daniel Micay <>,
        Eric Dumazet <>,
        Christoph Lameter <>,
        Pekka Enberg <>,
        David Rientjes <>,
        Joonsoo Kim <>,
        Matthias Schiffer <>,
        Andrew Morton <>,
        Linus Torvalds <>,
        Sven Eckelmann <>,
        Sasha Levin <>
Subject: [PATCH 4.14 023/117] mm, slub: restore the original intention of prefetch_freepointer()

From: Vlastimil Babka <>

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.

Fixes: 2482ddec670f ("mm: add SLUB free list pointer obfuscation")
Signed-off-by: Vlastimil Babka <>
Acked-by: Kees Cook <>
Cc: Daniel Micay <>
Cc: Eric Dumazet <>
Cc: Christoph Lameter <>
Cc: Pekka Enberg <>
Cc: David Rientjes <>
Cc: Joonsoo Kim <>
Cc: Matthias Schiffer <>
Signed-off-by: Andrew Morton <>
Signed-off-by: Linus Torvalds <>
Signed-off-by: Sven Eckelmann <>
Signed-off-by: Sasha Levin <>
 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)

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