netdev - Re: [PATCH v2] net: mctp: Fix tx queue stall

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Message-ID: <a24255faaf750bad30adefa24b510d0ccbaf37b0.camel@codeconstruct.com.au>
Date: Mon, 27 Oct 2025 14:41:59 +0800
From: Jeremy Kerr <jk@...econstruct.com.au>
To: Jinliang Wang <jinliangw@...gle.com>, Matt Johnston
	 <matt@...econstruct.com.au>, netdev@...r.kernel.org
Cc: Andrew Lunn <andrew+netdev@...n.ch>, "David S. Miller"
 <davem@...emloft.net>,  Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski
 <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] net: mctp: Fix tx queue stall

Hi Jinliang,

Thanks for the fix! A couple of comments on the metadata:

> Subject: [PATCH v2] net: mctp: Fix tx queue stall

You'll want to indicate that this is for net rather than net-next in
the subject prefix, so:

> Subject: [PATCH net v2] net: mctp: Fix tx queue stall

Then, since we're targeting net, we'll want a fixes tag too. I would
suggest:

Fixes: 0791c0327a6e ("net: mctp: Add MCTP USB transport driver")

- so we get appropriate backports. No need to reply to the original
message for subsequent versions either, a new thread is best.

Also, it's helpful to indicate changes between submitted versions,
under the '---' marker, which doesn't end up in the git commit.
Something like:

---
v3:
 - target net tree, add fixes tag

v2:
 - remove duplicate comment in commit message

---
 drivers/net/mctp/mctp-usb.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

> 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.

LGTM. With the changes above:

Acked-by: Jeremy Kerr <jk@...econstruct.com.au>

Cheers,


Jeremy