Re: [PATCH] watchdog: imx_sc_wdt: fix pretimeout

[Guenter Roeck <linux@roeck-us.net>]

On 4/5/21 5:59 AM, eichest@gmail.com wrote:
> From: Stefan Eichenberger <eichest@gmail.com>
> 
> If the WDIOF_PRETIMEOUTE flag is not set when registering the device the

WDIOF_PRETIMEOUT

> driver will not show the sysfs entries or register the default governor.
> By moving the registering after the decision whether pretimeout is
> supported this gets fixed.
> 

This is problematic. If the notifier is called and the watchdog is not yet
registered, it will call watchdog_notify_pretimeout on an unregistered
watchdog device which would crash the system. The notifier function needs
to handle that situation. This is for both registration and removal: On
removal, the watchdog device would be unregistered first (because of the
use of devm_ functions) and, again, the notifier could be called on an
unregistered watchdog device.

> Signed-off-by: Stefan Eichenberger <eichest@gmail.com>
> ---
>  drivers/watchdog/imx_sc_wdt.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/watchdog/imx_sc_wdt.c b/drivers/watchdog/imx_sc_wdt.c
> index e9ee22a7cb45..eddb1ae630e0 100644
> --- a/drivers/watchdog/imx_sc_wdt.c
> +++ b/drivers/watchdog/imx_sc_wdt.c
> @@ -183,10 +183,6 @@ static int imx_sc_wdt_probe(struct platform_device *pdev)
>  	watchdog_stop_on_reboot(wdog);
>  	watchdog_stop_on_unregister(wdog);
>  
> -	ret = devm_watchdog_register_device(dev, wdog);
> -	if (ret)
> -		return ret;
> -
>  	ret = imx_scu_irq_group_enable(SC_IRQ_GROUP_WDOG,
>  				       SC_IRQ_WDOG,
>  				       true);
> @@ -213,6 +209,10 @@ static int imx_sc_wdt_probe(struct platform_device *pdev)
>  	else
>  		dev_warn(dev, "Add action failed, pretimeout NOT supported\n");
>  
> +	ret = devm_watchdog_register_device(dev, wdog);
> +	if (ret)
> +		return ret;
> +
>  	return 0;

This is equivalent to just "return ret;".

>  }
>  
>