[RFC][PATCH 2/4] futex: Use smp_store_release() in mark_wake_futex()

From: Peter Zijlstra <peterz@infradead.org>
To: mingo@kernel.org, tglx@linutronix.de, juri.lelli@arm.com,
	rostedt@goodmis.org, xlpang@redhat.com, bigeasy@linutronix.de
Cc: linux-kernel@vger.kernel.org, mathieu.desnoyers@efficios.com,
	jdesfossez@efficios.com, bristot@redhat.com,
	peterz@infradead.org
Subject: [RFC][PATCH 2/4] futex: Use smp_store_release() in mark_wake_futex()
Date: Mon, 03 Oct 2016 11:12:36 +0200	[thread overview]
Message-ID: <20161003091847.527807466@infradead.org> (raw)
In-Reply-To: 20161003091234.879763059@infradead.org

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Since the futex_q can dissapear the instruction after assigning NULL,
this really should be a RELEASE barrier. That stops loads from hitting
dead memory too.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 kernel/futex.c |    3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -1288,8 +1288,7 @@ static void mark_wake_futex(struct wake_
 	 * memory barrier is required here to prevent the following
 	 * store to lock_ptr from getting ahead of the plist_del.
 	 */
-	smp_wmb();
-	q->lock_ptr = NULL;
+	smp_store_release(&q->lock_ptr, NULL);
 }
 
 static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *top_waiter,
