enic: move wmb closer to where needed: before writing posted_index to hw

Signed-off-by: Scott Feldman <scofeldm@cisco.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 8 insertions, 1 deletions

diff --git a/drivers/net/enic/vnic_rq.h b/drivers/net/enic/vnic_rq.h
index 82bfca67cc4d..fd0ef66d2e9f 100644
--- a/drivers/net/enic/vnic_rq.h
+++ b/drivers/net/enic/vnic_rq.h
@@ -132,8 +132,15 @@ static inline void vnic_rq_post(struct vnic_rq *rq,
 #define VNIC_RQ_RETURN_RATE             0xf     /* keep 2^n - 1 */
 #endif
 
-        if ((buf->index & VNIC_RQ_RETURN_RATE) == 0)
+        if ((buf->index & VNIC_RQ_RETURN_RATE) == 0) {
+                /* Adding write memory barrier prevents compiler and/or CPU
+                 * reordering, thus avoiding descriptor posting before
+                 * descriptor is initialized. Otherwise, hardware can read
+                 * stale descriptor fields.
+                 */
+                wmb();
                 iowrite32(buf->index, &rq->ctrl->posted_index);
+        }
 }
 
 static inline void vnic_rq_return_descs(struct vnic_rq *rq, unsigned int count)