Re: [PATCH v2 1/2] nbd: mark the socket dead when a partial send times out

[Ming Lei <tom.leiming@gmail.com>]

On Mon, Sep 28, 2026 at 05:10:20PM +0800, Joseph Qi wrote:
> nbd_pending_cmd_work() completes the request with BLK_STS_IOERR once its
> retry loop passes req->deadline, but leaves nsock->pending set.  Nothing
> else clears it: nbd_send_cmd() only does so at its out: label after a
> complete send, and nbd_requeue_cmd() does not touch it.
> 
> Every later request on that socket then takes this branch in
> nbd_handle_cmd():
> 
> 	if (unlikely(nsock->pending && nsock->pending != req)) {
> 		nbd_requeue_cmd(cmd);
> 
> and is requeued again, forever, since the requeue path does not clear
> ->pending either.  If the tag is recycled first, ->pending matches the new
> request instead and nbd_send_cmd() resumes it in place of the abandoned
> one, skipping its header and leaving cmd_cookie alone.
> 
> Neither case leaves a usable socket.  The header went out and the rest of
> the payload never will, so the stream no longer matches what the server
> expects.  Mark the socket dead, which shuts it down and clears the partial
> send state.  nbd_xmit_timeout() does the same for a timed out request and
> only skips it here because NBD_CMD_PARTIAL_SEND makes it defer to this
> work function.
> 
> Without this, a write issued after the deadline fires never completes and
> the device has to be torn down to recover.
> 
> Reproduced by making the resumed send never progress, so the retry loop
> runs out req->deadline.  With the socket marked dead a later request is
> dispatched instead of requeued, and a reconnect afterwards does clean
> O_DIRECT I/O with no oops or warning.
> 
> Fixes: 8337b029f788 ("nbd: fix partial sending")
> Cc: stable@vger.kernel.org
> Signed-off-by: Joseph Qi <joseph.qi@linux.alibaba.com>
> ---
>  drivers/block/nbd.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
> index ffce519bf008..c2c3dbdd631f 100644
> --- a/drivers/block/nbd.c
> +++ b/drivers/block/nbd.c
> @@ -838,6 +838,14 @@ static void nbd_pending_cmd_work(struct work_struct *work)
>  		/* don't bother timeout handler for partial sending */
>  		if (READ_ONCE(jiffies) + msecs_to_jiffies(wait_ms) >= deadline) {
>  			cmd->status = BLK_STS_IOERR;
> +			/*
> +			 * The header is on the wire but the rest of the payload
> +			 * never will be, so the stream is out of sync with the
> +			 * server.  Marking the socket dead also drops the stale
> +			 * nsock->pending, which would otherwise make
> +			 * nbd_handle_cmd() requeue every later request forever.
> +			 */
> +			nbd_mark_nsock_dead(nbd, nsock, 1);

Reviewed-by: Ming Lei <tom.leiming@gmail.com>


Thanks,
Ming