On 8/24/18 8:42 AM, 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.
Signed-off-by: Aaron Knister <aaron.s.knister@xxxxxxxx>
---
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 6535d9be..a620701f 100644
--- a/drivers/infiniband/ulp/ipoib/ipoib_cm.c
+++ b/drivers/infiniband/ulp/ipoib/ipoib_cm.c
@@ -1028,12 +1028,14 @@ 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;
Does this patch look OK to everyone? If so, is there anything additional
I can do for it to be considered for acceptance and merging?
Thanks!
-Aaron
--
Aaron Knister
NASA Center for Climate Simulation (Code 606.2)
Goddard Space Flight Center
(301) 286-2776
