From b0cffed54338e19e3cc46c9963478223eee0d560 Mon Sep 17 00:00:00 2001 From: Sowmini Varadhan Date: Sat, 8 Nov 2014 20:41:53 -0500 Subject: [PATCH] sunvnet: Fix race between vnet_start_xmit() and vnet_ack() When vnet_start_xmit() is concurrent with vnet_ack(), we may have a race that looks like: thread 1 thread 2 vnet_start_xmit vnet_event_napi -> vnet_rx __vnet_tx_trigger for some desc X at this point dr->prod == X peer sends back a stopped ack for X we process X, but X == dr->prod so we bail out in vnet_ack with !idx_is_pending update dr->prod As a result of the fact that we never processed the stopped ack for X, the Tx path is led to incorrectly believe that the peer is still "started" and reading, but the peer has stopped reading, which will ultimately end in flow-control assertions. The fix is to synchronize the above 2 paths on the netif_tx_lock. Signed-off-by: Sowmini Varadhan Signed-off-by: David S. Miller --- drivers/net/ethernet/sun/sunvnet.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) diff --git a/drivers/net/ethernet/sun/sunvnet.c b/drivers/net/ethernet/sun/sunvnet.c index 5c5fb59adf76..deb395a82e50 100644 --- a/drivers/net/ethernet/sun/sunvnet.c +++ b/drivers/net/ethernet/sun/sunvnet.c @@ -559,15 +559,17 @@ static int vnet_ack(struct vnet_port *port, void *msgbuf) return 0; end = pkt->end_idx; - if (unlikely(!idx_is_pending(dr, end))) - return 0; - vp = port->vp; dev = vp->dev; + netif_tx_lock(dev); + if (unlikely(!idx_is_pending(dr, end))) { + netif_tx_unlock(dev); + return 0; + } + /* sync for race conditions with vnet_start_xmit() and tell xmit it * is time to send a trigger. */ - netif_tx_lock(dev); dr->cons = next_idx(end, dr); desc = vio_dring_entry(dr, dr->cons); if (desc->hdr.state == VIO_DESC_READY && port->start_cons) { -- 2.20.1