From b8b9c7f05b3cd11560c0d98dfbb20e06e68cb70e Mon Sep 17 00:00:00 2001 From: Aaron Knister Date: Fri, 24 Aug 2018 08:42:46 -0400 Subject: [PATCH] IB/ipoib: Avoid a race condition between start_xmit and cm_rep_handler 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") Cc: stable@vger.kernel.org Signed-off-by: Aaron Knister Tested-by: Ira Weiny Reviewed-by: Ira Weiny Signed-off-by: Jason Gunthorpe Signed-off-by: Greg Kroah-Hartman --- drivers/infiniband/ulp/ipoib/ipoib_cm.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/drivers/infiniband/ulp/ipoib/ipoib_cm.c b/drivers/infiniband/ulp/ipoib/ipoib_cm.c index 7a5ed5a..9939f32 100644 --- a/drivers/infiniband/ulp/ipoib/ipoib_cm.c +++ b/drivers/infiniband/ulp/ipoib/ipoib_cm.c @@ -1018,12 +1018,14 @@ static int ipoib_cm_rep_handler(struct ib_cm_id *cm_id, struct ib_cm_event *even 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; -- 2.7.4