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Date
SubjectRe: [PATCH] net: ethernet: ti: cpsw: fix net watchdog timeout
From
From: Grygorii Strashko <grygorii.strashko@ti.com>
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@ti.com>

Applied, thanks.

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