Re: [PATCH net v7 3/3] net: sched: fix tx action reschedule issue with stopped queue

[Jakub Kicinski]

On Thu, 13 May 2021 09:11:00 +0800 Yunsheng Lin wrote:
> The netdev qeueue might be stopped when byte queue limit has
> reached or tx hw ring is full, net_tx_action() may still be
> rescheduled endlessly if STATE_MISSED is set, which consumes
> a lot of cpu without dequeuing and transmiting any skb because
> the netdev queue is stopped, see qdisc_run_end().
> 
> This patch fixes it by checking the netdev queue state before
> calling qdisc_run() and clearing STATE_MISSED if netdev queue is
> stopped during qdisc_run(), the net_tx_action() is recheduled
> again when netdev qeueue is restarted, see netif_tx_wake_queue().
> 
> As there is time window betewwn netif_xmit_frozen_or_stopped()
> checking and STATE_MISSED clearing, between which STATE_MISSED
> is set by net_tx_action() scheduled by netif_tx_wake_queue(),
> so set the STATE_MISSED again if netdev queue is restarted.
> 
> Fixes: 6b3ba9146fe6 ("net: sched: allow qdiscs to handle locking")
> Reported-by: Michal Kubecek <mkubecek@xxxxxxx>
> Signed-off-by: Yunsheng Lin <linyunsheng@xxxxxxxxxx>

> @@ -35,6 +35,25 @@
>  const struct Qdisc_ops *default_qdisc_ops = &pfifo_fast_ops;
>  EXPORT_SYMBOL(default_qdisc_ops);
>  
> +static void qdisc_maybe_stop_tx(struct Qdisc *q,

nit: qdisc_maybe_clear_missed()?