From: "Michael S. Tsirkin" <mst@redhat.com>
Date: Fri, 26 Jan 2018 01:36:38 +0200
Subject: ptr_ring: prevent queue load/store tearing
Patch-mainline: v4.16-rc1
Git-commit: a07d29c6724a19eab120b7a74a9bfd107d20f69a
References: bsc#1109837

In theory compiler could tear queue loads or stores in two. It does not
seem to be happening in practice but it seems easier to convert the
cases where this would be a problem to READ/WRITE_ONCE than worry about
it.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
---
 include/linux/ptr_ring.h |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/include/linux/ptr_ring.h
+++ b/include/linux/ptr_ring.h
@@ -114,7 +114,7 @@ static inline int __ptr_ring_produce(str
 	/* Pairs with smp_read_barrier_depends in __ptr_ring_consume. */
 	smp_wmb();
 
-	r->queue[r->producer++] = ptr;
+	WRITE_ONCE(r->queue[r->producer++], ptr);
 	if (unlikely(r->producer >= r->size))
 		r->producer = 0;
 	return 0;
@@ -173,7 +173,7 @@ static inline int ptr_ring_produce_bh(st
 static inline void *__ptr_ring_peek(struct ptr_ring *r)
 {
 	if (likely(r->size))
-		return r->queue[r->consumer_head];
+		return READ_ONCE(r->queue[r->consumer_head]);
 	return NULL;
 }