netdev - Re: [PATCH net-next] net: ag71xx: disable napi interrupts during probe

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Message-ID: <cabb111b-37b4-493c-ad6c-c237c7091bf6@intel.com>
Date: Wed, 28 Aug 2024 14:05:46 -0700
From: Jacob Keller <jacob.e.keller@...el.com>
To: Rosen Penev <rosenp@...il.com>, <netdev@...r.kernel.org>
CC: <davem@...emloft.net>, <edumazet@...gle.com>, <kuba@...nel.org>,
	<pabeni@...hat.com>, <linux@...linux.org.uk>, <linux-kernel@...r.kernel.org>,
	<o.rempel@...gutronix.de>, <p.zabel@...gutronix.de>
Subject: Re: [PATCH net-next] net: ag71xx: disable napi interrupts during
 probe



On 8/28/2024 1:41 PM, Rosen Penev wrote:
> From: Sven Eckelmann <sven@...fation.org>
> 
> ag71xx_probe is registering ag71xx_interrupt as handler for gmac0/gmac1
> interrupts. The handler is trying to use napi_schedule to handle the
> processing of packets. But the netif_napi_add for this device is
> called a lot later in ag71xx_probe.
> 
> It can therefore happen that a still running gmac0/gmac1 is triggering the
> interrupt handler with a bit from AG71XX_INT_POLL set in
> AG71XX_REG_INT_STATUS. The handler will then call napi_schedule and the
> napi code will crash the system because the ag->napi is not yet
> initialized.
> 
> The gmcc0/gmac1 must be brought in a state in which it doesn't signal a
> AG71XX_INT_POLL related status bits as interrupt before registering the
> interrupt handler. ag71xx_hw_start will take care of re-initializing the
> AG71XX_REG_INT_ENABLE.
> 
> Signed-off-by: Sven Eckelmann <sven@...fation.org>
> Signed-off-by: Rosen Penev <rosenp@...il.com>
> ---

The description reads like a bug fix, so I would expect this to be
targeted to net and have a Fixes tag indicating what commit introduced
the issue, maybe:

Fixes: d51b6ce441d3 ("net: ethernet: add ag71xx driver")

The change seems reasonable to me otherwise.

>  drivers/net/ethernet/atheros/ag71xx.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/net/ethernet/atheros/ag71xx.c b/drivers/net/ethernet/atheros/ag71xx.c
> index 0674a042e8d3..435c4b19acdd 100644
> --- a/drivers/net/ethernet/atheros/ag71xx.c
> +++ b/drivers/net/ethernet/atheros/ag71xx.c
> @@ -1855,6 +1855,12 @@ static int ag71xx_probe(struct platform_device *pdev)
>  	if (!ag->mac_base)
>  		return -ENOMEM;
>  
> +	/* ensure that HW is in manual polling mode before interrupts are
> +	 * activated. Otherwise ag71xx_interrupt might call napi_schedule
> +	 * before it is initialized by netif_napi_add.
> +	 */
> +	ag71xx_int_disable(ag, AG71XX_INT_POLL);
> +
>  	ndev->irq = platform_get_irq(pdev, 0);
>  	err = devm_request_irq(&pdev->dev, ndev->irq, ag71xx_interrupt,
>  			       0x0, dev_name(&pdev->dev), ndev);