netdev - Re: [PATCH net v2 3/4] bnxt: make sure xmit_more + errors does not miss doorbells

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Date:   Wed, 11 Aug 2021 23:51:25 -0700
From:   Michael Chan <michael.chan@...adcom.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     David Miller <davem@...emloft.net>,
        Jeffrey Huang <huangjw@...adcom.com>,
        Eddie Wai <eddie.wai@...adcom.com>,
        Prashant Sreedharan <prashant@...adcom.com>,
        Andrew Gospodarek <gospo@...adcom.com>,
        Netdev <netdev@...r.kernel.org>,
        Edwin Peer <edwin.peer@...adcom.com>
Subject: Re: [PATCH net v2 3/4] bnxt: make sure xmit_more + errors does not
 miss doorbells

On Wed, Aug 11, 2021 at 2:38 PM Jakub Kicinski <kuba@...nel.org> wrote:

> @@ -396,6 +404,8 @@ static netdev_tx_t bnxt_start_xmit(struct sk_buff *skb, struct net_device *dev)
>         free_size = bnxt_tx_avail(bp, txr);
>         if (unlikely(free_size < skb_shinfo(skb)->nr_frags + 2)) {
>                 netif_tx_stop_queue(txq);
> +               if (net_ratelimit() && txr->kick_pending)
> +                       netif_warn(bp, tx_err, dev, "bnxt: ring busy!\n");

I think there is one more problem here.  Now that it is possible to
get here, we can race with bnxt_tx_int() again here.  We can call
netif_tx_stop_queue() here after bnxt_tx_int() has already cleaned the
entire TX ring.  So I think we need to call bnxt_tx_wake_queue() here
again if descriptors have become available.

>                 return NETDEV_TX_BUSY;
>         }
>

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