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bna: Add synchronization for tx ring.

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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>
This commit is contained in:
Benjamin Poirier 2016-11-07 17:57:56 +08:00 committed by David S. Miller
parent f91d718156
commit d667f78514
1 changed files with 2 additions and 2 deletions
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4
drivers/net/ethernet/brocade/bna/bnad.c
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@ -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;
}