On Fri, Aug 24, 2018 at 08:42:46AM -0400, Aaron Knister wrote:
> 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@xxxxxxxxxxxxxxx
> Signed-off-by: Aaron Knister <aaron.s.knister@xxxxxxxx>
> Tested-by: Ira Weiny <ira.weiny@xxxxxxxxx>
> Reviewed-by: Ira Weiny <ira.weiny@xxxxxxxxx>
> Signed-off-by: Jason Gunthorpe <jgg@xxxxxxxxxxxx>
> ---
> drivers/infiniband/ulp/ipoib/ipoib_cm.c | 2 ++
> 1 file changed, 2 insertions(+)
Thanks, I added a cc stable and queued this to for-rc
Jason
