3.16.62-rc1 review patch. If anyone has any objections, please let me know.
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From: Aaron Knister aaron.s.knister@nasa.gov
commit 816e846c2eb9129a3e0afa5f920c8bbc71efecaa upstream.
Inside of start_xmit() the call to check if the connection is up and the queueing of the packets for later transmission is not atomic which leaves a window where cm_rep_handler can run, set the connection up, dequeue pending packets and leave the subsequently queued packets by start_xmit() sitting on neigh->queue until they're dropped when the connection is torn down. This only applies to connected mode. These dropped packets can really upset TCP, for example, and cause multi-minute delays in transmission for open connections.
Here's the code in start_xmit where we check to see if the connection is up:
if (ipoib_cm_get(neigh)) { if (ipoib_cm_up(neigh)) { ipoib_cm_send(dev, skb, ipoib_cm_get(neigh)); goto unref; } }
The race occurs if cm_rep_handler execution occurs after the above connection check (specifically if it gets to the point where it acquires priv->lock to dequeue pending skb's) but before the below code snippet in start_xmit where packets are queued.
if (skb_queue_len(&neigh->queue) < IPOIB_MAX_PATH_REC_QUEUE) { push_pseudo_header(skb, phdr->hwaddr); spin_lock_irqsave(&priv->lock, flags); __skb_queue_tail(&neigh->queue, skb); spin_unlock_irqrestore(&priv->lock, flags); } else { ++dev->stats.tx_dropped; dev_kfree_skb_any(skb); }
The patch acquires the netif tx lock in cm_rep_handler for the section where it sets the connection up and dequeues and retransmits deferred skb's.
Fixes: 839fcaba355a ("IPoIB: Connected mode experimental support") Signed-off-by: Aaron Knister aaron.s.knister@nasa.gov Tested-by: Ira Weiny ira.weiny@intel.com Reviewed-by: Ira Weiny ira.weiny@intel.com Signed-off-by: Jason Gunthorpe jgg@mellanox.com Signed-off-by: Ben Hutchings ben@decadent.org.uk --- drivers/infiniband/ulp/ipoib/ipoib_cm.c | 2 ++ 1 file changed, 2 insertions(+)
--- a/drivers/infiniband/ulp/ipoib/ipoib_cm.c +++ b/drivers/infiniband/ulp/ipoib/ipoib_cm.c @@ -996,12 +996,14 @@ static int ipoib_cm_rep_handler(struct i
skb_queue_head_init(&skqueue);
+ netif_tx_lock_bh(p->dev); spin_lock_irq(&priv->lock); set_bit(IPOIB_FLAG_OPER_UP, &p->flags); if (p->neigh) while ((skb = __skb_dequeue(&p->neigh->queue))) __skb_queue_tail(&skqueue, skb); spin_unlock_irq(&priv->lock); + netif_tx_unlock_bh(p->dev);
while ((skb = __skb_dequeue(&skqueue))) { skb->dev = p->dev;