linux-kernel - [PATCH] slub: Hold list_lock unconditionally before the call to add

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Message-ID: <20140207184653.GA5799@in.ibm.com>
Date:	Sat, 8 Feb 2014 00:16:53 +0530
From:	Gautham R Shenoy <ego@...ux.vnet.ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	peterz@...radead.org, penberg@...nel.org
Subject: [PATCH] slub: Hold list_lock unconditionally before the call to
 add_full.

Hi,

>From the lockdep annotation and the comment that existed before the
lockdep annotations were introduced, 
mm/slub.c:add_full(s, n, page) expects to be called with n->list_lock
held.

However, there's a call path in deactivate_slab() when

	 (new.inuse || n->nr_partial <= s->min_partial) &&
	 !(new.freelist) &&
         !(kmem_cache_debug(s))

which ends up calling add_full() without holding
n->list_lock.

This was discovered while onlining/offlining cpus in 3.14-rc1 due to
the lockdep annotations added by commit
c65c1877bd6826ce0d9713d76e30a7bed8e49f38.

Fix this by unconditionally taking the lock
irrespective of the state of kmem_cache_debug(s).

Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Pekka Enberg <penberg@...nel.org>
Signed-off-by: Gautham R. Shenoy <ego@...ux.vnet.ibm.com>
---
 mm/slub.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/slub.c b/mm/slub.c
index 7e3e045..1f723f7 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1882,7 +1882,7 @@ redo:
 		}
 	} else {
 		m = M_FULL;
-		if (kmem_cache_debug(s) && !lock) {
+		if (!lock) {
 			lock = 1;
 			/*
 			 * This also ensures that the scanning of full
-- 
1.8.3.1

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