IB/ipath: Add barrier before updating WC head in shared memory

Add a barrier to make sure the CPU doesn't reorder writes to memory,
since user programs can be polling on the head index update and the
entry should be written before that.

Signed-off-by: Ralph Campbell <ralph.campbell@qlogic.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/drivers/infiniband/hw/ipath/ipath_ud.c b/drivers/infiniband/hw/ipath/ipath_ud.c
index 38ba771b3efe..f9a3338a5fb7 100644
--- a/drivers/infiniband/hw/ipath/ipath_ud.c
+++ b/drivers/infiniband/hw/ipath/ipath_ud.c
@@ -176,6 +176,8 @@ static void ipath_ud_loopback(struct ipath_qp *sqp,
                         dev->n_pkt_drops++;
                         goto bail_sge;
                 }
+                /* Make sure entry is read after head index is read. */
+                smp_rmb();
                 wqe = get_rwqe_ptr(rq, tail);
                 if (++tail >= rq->size)
                         tail = 0;