Re: [PATCH] net: ethernet: ti: cpsw: fix net watchdog timeout

[Grygorii Strashko]

On 02/07/2018 08:57 PM, David Miller wrote:
> From: Grygorii Strashko <grygorii.strashko@xxxxxx>
> Date: Tue, 6 Feb 2018 19:17:06 -0600
>
> > It was discovered that simple program which indefinitely sends 200b UDP
> > packets and runs on TI AM574x SoC (SMP) under RT Kernel triggers network
> > watchdog timeout in TI CPSW driver (<6 hours run). The network watchdog
> > timeout is triggered due to race between cpsw_ndo_start_xmit() and
> > cpsw_tx_handler() [NAPI]
> >
> > cpsw_ndo_start_xmit()
> > 	if (unlikely(!cpdma_check_free_tx_desc(txch))) {
> > 		txq = netdev_get_tx_queue(ndev, q_idx);
> > 		netif_tx_stop_queue(txq);
> >
> > ^^ as per [1] barier has to be used after set_bit() otherwise new value
> > might not be visible to other cpus
> > 	}
> >
> > cpsw_tx_handler()
> > 	if (unlikely(netif_tx_queue_stopped(txq)))
> > 		netif_tx_wake_queue(txq);
> >
> > and when it happens ndev TX queue became disabled forever while driver's HW
> > TX queue is empty.
> >
> > Fix this, by adding smp_mb__after_atomic() after netif_tx_stop_queue()
> > calls and double check for free TX descriptors after stopping ndev TX queue
> > - if there are free TX descriptors wake up ndev TX queue.
> >
> > [1] https://www.kernel.org/doc/html/latest/core-api/atomic_ops.html
> > Signed-off-by: Grygorii Strashko <grygorii.strashko@xxxxxx>
>
> Applied, thanks.

Thank you David.

Could this be marked as stable material 4.9+?

--
regards,
-grygorii