linux-kernel - [PATCH tip/core/rcu 21/21] drivers/vhost: Remove now-redundant read_barrier

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Date:   Fri,  1 Dec 2017 11:51:16 -0800
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     linux-kernel@...r.kernel.org
Cc:     mingo@...nel.org, jiangshanlai@...il.com, dipankar@...ibm.com,
        akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
        josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
        rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
        fweisbec@...il.com, oleg@...hat.com,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>, <kvm@...r.kernel.org>,
        <virtualization@...ts.linux-foundation.org>,
        <netdev@...r.kernel.org>
Subject: [PATCH tip/core/rcu 21/21] drivers/vhost: Remove now-redundant read_barrier_depends()

Because READ_ONCE() now implies read_barrier_depends(), the
read_barrier_depends() in next_desc() is now redundant.  This commit
therefore removes it and the related comments.

Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Cc: "Michael S. Tsirkin" <mst@...hat.com>
Cc: Jason Wang <jasowang@...hat.com>
Cc: <kvm@...r.kernel.org>
Cc: <virtualization@...ts.linux-foundation.org>
Cc: <netdev@...r.kernel.org>
---
 drivers/vhost/vhost.c | 7 +------
 1 file changed, 1 insertion(+), 6 deletions(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 33ac2b186b85..78b5940a415a 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -1877,12 +1877,7 @@ static unsigned next_desc(struct vhost_virtqueue *vq, struct vring_desc *desc)
 		return -1U;
 
 	/* Check they're not leading us off end of descriptors. */
-	next = vhost16_to_cpu(vq, desc->next);
-	/* Make sure compiler knows to grab that: we don't want it changing! */
-	/* We will use the result as an index in an array, so most
-	 * architectures only need a compiler barrier here. */
-	read_barrier_depends();
-
+	next = vhost16_to_cpu(vq, READ_ONCE(desc->next));
 	return next;
 }
 
-- 
2.5.2