bna: CQ Read Fix

Valid bit check for completion needs read fence, so that it does not get
reordered with other loads.

Signed-off-by: Rasesh Mody <rmody@brocade.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/ethernet/brocade/bna/bnad.c b/drivers/net/ethernet/brocade/bna/bnad.c
index 3061dc5..7d818de 100644 (file)
--- a/drivers/net/ethernet/brocade/bna/bnad.c
+++ b/drivers/net/ethernet/brocade/bna/bnad.c
@@ -601,7 +601,18 @@ bnad_cq_process(struct bnad *bnad, struct bna_ccb *ccb, int budget)
        cq = ccb->sw_q;
        cmpl = &cq[ccb->producer_index];
 
-       while (cmpl->valid && (packets < budget)) {
+       while (packets < budget) {
+               if (!cmpl->valid)
+                       break;
+               /* The 'valid' field is set by the adapter, only after writing
+                * the other fields of completion entry. Hence, do not load
+                * other fields of completion entry *before* the 'valid' is
+                * loaded. Adding the rmb() here prevents the compiler and/or
+                * CPU from reordering the reads which would potentially result
+                * in reading stale values in completion entry.
+                */
+               rmb();
+
                BNA_UPDATE_PKT_CNT(pkt_rt, ntohs(cmpl->length));
 
                if (bna_is_small_rxq(cmpl->rxq_id))
@@ -641,6 +652,16 @@ bnad_cq_process(struct bnad *bnad, struct bna_ccb *ccb, int budget)
 
                                if (!next_cmpl->valid)
                                        break;
+                               /* The 'valid' field is set by the adapter, only
+                                * after writing the other fields of completion
+                                * entry. Hence, do not load other fields of
+                                * completion entry *before* the 'valid' is
+                                * loaded. Adding the rmb() here prevents the
+                                * compiler and/or CPU from reordering the reads
+                                * which would potentially result in reading
+                                * stale values in completion entry.
+                                */
+                               rmb();
 
                                len = ntohs(next_cmpl->length);
                                flags = ntohl(next_cmpl->flags);