[PATCH 3.10 123/268] bna: Add synchronization for tx ring.

Willy Tarreau
2017-06-19T18:39:15Z

From: Benjamin Poirier <bpoirier@suse.com>

commit d667f78514c656a6a8bf0b3d6134a7fe5cd4d317 upstream.

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>
Signed-off-by: Willy Tarreau <w@1wt.eu>
---
drivers/net/ethernet/brocade/bna/bnad.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/brocade/bna/bnad.c b/drivers/net/ethernet/brocade/bna/bnad.c
index 07f7ef0..d18ee75 100644
--- a/drivers/net/ethernet/brocade/bna/bnad.c
+++ b/drivers/net/ethernet/brocade/bna/bnad.c
@@ -193,6 +193,7 @@ 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;

@@ -2903,13 +2904,12 @@ 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;

bna_txq_prod_indx_doorbell(tcb);
- smp_mb();

return NETDEV_TX_OK;
}
--
2.8.0.rc2.1.gbe9624a