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Subject: Re: [PATCH net] net: lantiq: disable interrupt before sheduling NAPI
To:     Aleksander Jan Bajkowski <olek2@wp.pl>, davem@davemloft.net,
        kuba@kernel.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <20210608212107.222690-1-olek2@wp.pl>
From:   Hauke Mehrtens <hauke@hauke-m.de>
Message-ID: <c951fd28-443e-9445-0be3-b134c888f4dc@hauke-m.de>
Date:   Tue, 8 Jun 2021 23:33:34 +0200
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In-Reply-To: <20210608212107.222690-1-olek2@wp.pl>
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Precedence: bulk

On 6/8/21 11:21 PM, Aleksander Jan Bajkowski wrote:
> This patch fixes TX hangs with threaded NAPI enabled. The scheduled
> NAPI seems to be executed in parallel with the interrupt on second
> thread. Sometimes it happens that ltq_dma_disable_irq() is executed
> after xrx200_tx_housekeeping(). The symptom is that TX interrupts
> are disabled in the DMA controller. As a result, the TX hangs after
> a few seconds of the iperf test. Scheduling NAPI after disabling
> interrupts fixes this issue.
> 
> Tested on Lantiq xRX200 (BT Home Hub 5A).
> 
> Fixes: 9423361da523 ("net: lantiq: Disable IRQs only if NAPI gets scheduled ")
> Signed-off-by: Aleksander Jan Bajkowski <olek2@wp.pl>

Acked-by: Hauke Mehrtens <hauke@hauke-m.de>

> ---
>   drivers/net/ethernet/lantiq_xrx200.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/lantiq_xrx200.c b/drivers/net/ethernet/lantiq_xrx200.c
> index 36dc3e5f6218..0e10d8aeffe1 100644
> --- a/drivers/net/ethernet/lantiq_xrx200.c
> +++ b/drivers/net/ethernet/lantiq_xrx200.c
> @@ -352,8 +352,8 @@ static irqreturn_t xrx200_dma_irq(int irq, void *ptr)
>   	struct xrx200_chan *ch = ptr;
>   
>   	if (napi_schedule_prep(&ch->napi)) {
> -		__napi_schedule(&ch->napi);
>   		ltq_dma_disable_irq(&ch->dma);
> +		__napi_schedule(&ch->napi);
>   	}
>   
>   	ltq_dma_ack_irq(&ch->dma);
>