netdev - Re: [Patch net-next v3 3/3] net_sched: implement ->change_tx_queue_len() for pfifo

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Date:   Sun, 28 Jan 2018 18:33:28 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     Jason Wang <jasowang@...hat.com>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        John Fastabend <john.fastabend@...il.com>
Subject: Re: [Patch net-next v3 3/3] net_sched: implement ->change_tx_queue_len()
 for pfifo_fast

On Fri, Jan 26, 2018 at 6:10 AM, Michael S. Tsirkin <mst@...hat.com> wrote:
>
> This part?

Yes, dev_deactivate() as you quote.

>
> +       bool up = dev->flags & IFF_UP;
> +       unsigned int i;
> +       int ret = 0;
> +
> +       if (up)
> +               dev_deactivate(dev);
> +
> +       for (i = 0; i < dev->num_tx_queues; i++) {
> +               ret = qdisc_change_tx_queue_len(dev, &dev->_tx[i]);
> +
> +               /* TODO: revert changes on a partial failure */
> +               if (ret)
> +                       break;
> +       }
> +
> +       if (up)
> +               dev_activate(dev);
>
>
> I wonder whether it really is safe to read dev->flags like that
> without any locks.

I really to hate to point it out again we have RTNL here. You
missed my previous response to John. ;)

Please read v1 and v2 when you response to v3.