bna: Add synchronization for tx ring.

We received two reports of BUG_ON in bnad_txcmpl_process() where
hw_consumer_index appeared to be ahead of producer_index. Out of order
write/read of these variables could explain these reports.

bnad_start_xmit(), as a producer of tx descriptors, has a few memory
barriers sprinkled around writes to producer_index and the device's
doorbell but they're not paired with anything in bnad_txcmpl_process(), a
consumer.

Since we are synchronizing with a device, we must use mandatory barriers,
not smp_*. Also, I didn't see the purpose of the last smp_mb() in
bnad_start_xmit().

Signed-off-by: Benjamin Poirier <bpoirier@suse.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 f9df4b5ae90e091d7bd440e16d87ef404ab1ba80..f42f672b0e7eab91e3cc90dece31bf691eb02bc8 100644 (file)
--- a/drivers/net/ethernet/brocade/bna/bnad.c
+++ b/drivers/net/ethernet/brocade/bna/bnad.c
@@ -177,6 +177,7 @@ bnad_txcmpl_process(struct bnad *bnad, struct bna_tcb *tcb)
                return 0;
 
        hw_cons = *(tcb->hw_consumer_index);
+       rmb();
        cons = tcb->consumer_index;
        q_depth = tcb->q_depth;
 
@@ -3094,7 +3095,7 @@ bnad_start_xmit(struct sk_buff *skb, struct net_device *netdev)
        BNA_QE_INDX_INC(prod, q_depth);
        tcb->producer_index = prod;
 
-       smp_mb();
+       wmb();
 
        if (unlikely(!test_bit(BNAD_TXQ_TX_STARTED, &tcb->flags)))
                return NETDEV_TX_OK;
@@ -3102,7 +3103,6 @@ bnad_start_xmit(struct sk_buff *skb, struct net_device *netdev)
        skb_tx_timestamp(skb);
 
        bna_txq_prod_indx_doorbell(tcb);
-       smp_mb();
 
        return NETDEV_TX_OK;
 }