[Devel] [PATCH] ms/mm/slub.c: list_lock may not be held in some circumstances

[Dmitry Safonov]

From: David Rientjes <rientjes at google.com>

Commit c65c1877bd68 ("slub: use lockdep_assert_held") incorrectly
required that add_full() and remove_full() hold n->list_lock.  The lock
is only taken when kmem_cache_debug(s), since that's the only time it
actually does anything.

Require that the lock only be taken under such a condition.

Reported-by: Larry Finger <Larry.Finger at lwfinger.net>
Tested-by: Larry Finger <Larry.Finger at lwfinger.net>
Tested-by: Paul E. McKenney <paulmck at linux.vnet.ibm.com>
Acked-by: Christoph Lameter <cl at linux.com>
Cc: Pekka Enberg <penberg at kernel.org>
Signed-off-by: David Rientjes <rientjes at google.com>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>

[backported from ms commit 255d0884f563 ("mm/slub.c: list_lock may not
be held in some circumstances")]
Cc: Andrey Ryabinin <aryabinin at virtuozzo.com>
Signed-off-by: Dmitry Safonov <dsafonov at virtuozzo.com>
---
 mm/slub.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index c930b022c5be..fcebd145a1b6 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -960,21 +960,19 @@ static void trace(struct kmem_cache *s, struct page *page, void *object,
 static void add_full(struct kmem_cache *s,
 	struct kmem_cache_node *n, struct page *page)
 {
-	lockdep_assert_held(&n->list_lock);
-
 	if (!(s->flags & SLAB_STORE_USER))
 		return;
 
+	lockdep_assert_held(&n->list_lock);
 	list_add(&page->lru, &n->full);
 }
 
 static void remove_full(struct kmem_cache *s, struct kmem_cache_node *n, struct page *page)
 {
-	lockdep_assert_held(&n->list_lock);
-
 	if (!(s->flags & SLAB_STORE_USER))
 		return;
 
+	lockdep_assert_held(&n->list_lock);
 	list_del(&page->lru);
 }
 
-- 
2.10.2