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Date: Wed, 1 Nov 2023 14:08:00 -0700
From: Michael Chan <>
Subject: Re: [PATCH 2/2] tg3: Fix the TX ring stall

On Wed, Nov 1, 2023 at 12:19 PM <> wrote:
> From: Alex Pakhunov <>
> The TX ring maintained by the tg3 driver can end up in a state, when it
> has packets queued for sending but the NIC hardware is not informed, so no
> progress is made. This leads to a multi-second interruption in network
> traffic followed by dev_watchdog() firing and resetting the queue.
> The specific sequence of steps is:
> 1. tg3_start_xmit() is called at least once and queues packet(s) without
>    updating tnapi->prodmbox (netdev_xmit_more() returns true)
> 2. tg3_start_xmit() is called with an SKB which causes tg3_tso_bug() to be
>    called.
> 3. tg3_tso_bug() determines that the SKB is too large, ...
>         if (unlikely(tg3_tx_avail(tnapi) <= frag_cnt_est)) {
>    ... stops the queue, and returns NETDEV_TX_BUSY:
>         netif_tx_stop_queue(txq);
>         ...
>         if (tg3_tx_avail(tnapi) <= frag_cnt_est)
>                 return NETDEV_TX_BUSY;
> 4. Since all tg3_tso_bug() call sites directly return, the code updating
>    tnapi->prodmbox is skipped.

Thanks for the patch.  An alternative fix that may be simpler is to
add a goto after calling tg3_tso_bug().  Something like this:

        goto update_tx_mbox;

        if (!netdev_xmit_more() || netif_xmit_stopped())

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