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net: mctp: Fix tx queue stall

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The tx queue can become permanently stuck in a stopped state due to a
race condition between the URB submission path and its completion
callback.

The URB completion callback can run immediately after usb_submit_urb()
returns, before the submitting function calls netif_stop_queue(). If
this occurs, the queue state management becomes desynchronized, leading
to a stall where the queue is never woken.

Fix this by moving the netif_stop_queue() call to before submitting the
URB. This closes the race window by ensuring the network stack is aware
the queue is stopped before the URB completion can possibly run.

Fixes: 0791c0327a ("net: mctp: Add MCTP USB transport driver")
Signed-off-by: Jinliang Wang <jinliangw@google.com>
Acked-by: Jeremy Kerr <jk@codeconstruct.com.au>
Link: https://patch.msgid.link/20251027065530.2045724-1-jinliangw@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Jinliang Wang 2025-10-26 23:55:30 -07:00 • committed by Jakub Kicinski
parent 53110232c9
commit da2522df3f
1 changed files with 5 additions and 3 deletions
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8
drivers/net/mctp/mctp-usb.c
View file

@ -96,11 +96,13 @@ static netdev_tx_t mctp_usb_start_xmit(struct sk_buff *skb,
skb->data, skb->len,
mctp_usb_out_complete, skb);
/* Stops TX queue first to prevent race condition with URB complete */
netif_stop_queue(dev);
rc = usb_submit_urb(urb, GFP_ATOMIC);
if (rc)
if (rc) {
netif_wake_queue(dev);
goto err_drop;
else
netif_stop_queue(dev);
}
return NETDEV_TX_OK;