From b52b945200dc52e063ed38d144197d5d0dd952ad Mon Sep 17 00:00:00 2001
From: Andrew Morton <akpm@osdl.org>
Date: Fri, 23 Dec 2005 19:54:46 -0800
Subject: [PATCH] --- yaml --- r: 15321 b: refs/heads/master c:
 8e31108b9f41069d55cb9b019ac8262c55fd2616 h: refs/heads/master i:   15319:
 79a471b5a4a3107364407b2f1f78f8376f2abe34 v: v3

---
 [refs]               | 2 +-
 trunk/kernel/futex.c | 6 ++++++
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/[refs] b/[refs]
index ddeb1a0be42a..536e339da863 100644
--- a/[refs]
+++ b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 6003a93e7bf6c02f33c02976ff364785d4273295
+refs/heads/master: 8e31108b9f41069d55cb9b019ac8262c55fd2616
diff --git a/trunk/kernel/futex.c b/trunk/kernel/futex.c
index 5872e3507f35..5e71a6bf6f6b 100644
--- a/trunk/kernel/futex.c
+++ b/trunk/kernel/futex.c
@@ -270,7 +270,13 @@ static void wake_futex(struct futex_q *q)
 	/*
 	 * The waiting task can free the futex_q as soon as this is written,
 	 * without taking any locks.  This must come last.
+	 *
+	 * A memory barrier is required here to prevent the following store
+	 * to lock_ptr from getting ahead of the wakeup. Clearing the lock
+	 * at the end of wake_up_all() does not prevent this store from
+	 * moving.
 	 */
+	wmb();
 	q->lock_ptr = NULL;
 }