netdev - [tip:core/rcu] drivers/vhost: Remove now-redundant read_barrier

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Date:   Wed, 3 Jan 2018 08:08:47 -0800
From:   "tip-bot for Paul E. McKenney" <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     mst@...hat.com, tglx@...utronix.de,
        virtualization@...ts.linux-foundation.org,
        paulmck@...ux.vnet.ibm.com, kvm@...r.kernel.org,
        jasowang@...hat.com, netdev@...r.kernel.org, mingo@...nel.org,
        hpa@...or.com
Subject: [tip:core/rcu] drivers/vhost: Remove now-redundant
 read_barrier_depends()

Commit-ID:  3a5db0b108e0a40f08c2bcff6a675dbf632b91e0
Gitweb:     https://git.kernel.org/tip/3a5db0b108e0a40f08c2bcff6a675dbf632b91e0
Author:     Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
AuthorDate: Mon, 27 Nov 2017 09:45:10 -0800
Committer:  Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
CommitDate: Tue, 5 Dec 2017 11:57:55 -0800

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 33ac2b1..78b5940 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;
 }