[PATCH 4.9 18/60] mm/slub.c: fix random_seq offset destruction

From: Greg Kroah-Hartman
Date: Mon Feb 13 2017 - 08:22:27 EST

4.9-stable review patch. If anyone has any objections, please let me know.


From: Sean Rees <sean@xxxxxxxxxx>

commit a810007afe239d59c1115fcaa06eb5b480f876e9 upstream.

Commit 210e7a43fa90 ("mm: SLUB freelist randomization") broke USB hub
initialisation as described in


Bail out early from init_cache_random_seq if s->random_seq is already
initialised. This prevents destroying the previously computed
random_seq offsets later in the function.

If the offsets are destroyed, then shuffle_freelist will truncate
page->freelist to just the first object (orphaning the rest).

Fixes: 210e7a43fa90 ("mm: SLUB freelist randomization")
Link: http://lkml.kernel.org/r/20170207140707.20824-1-sean@xxxxxxxxxx
Signed-off-by: Sean Rees <sean@xxxxxxxxxx>
Reported-by: <userwithuid@xxxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: Pekka Enberg <penberg@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Cc: Thomas Garnier <thgarnie@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

mm/slub.c | 4 ++++
1 file changed, 4 insertions(+)

--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1419,6 +1419,10 @@ static int init_cache_random_seq(struct
int err;
unsigned long i, count = oo_objects(s->oo);

+ /* Bailout if already initialised */
+ if (s->random_seq)
+ return 0;
err = cache_random_seq_create(s, count, GFP_KERNEL);
if (err) {
pr_err("SLUB: Unable to initialize free list for %s\n",