Re: [PATCH] watchdog: imx_sc_wdt: fix pretimeout

[Stefan Eichenberger <eichest@gmail.com>]

Hi Guenter,

On Mon, Apr 05, 2021 at 07:42:20AM -0700, Guenter Roeck wrote:
> 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
> 

Thanks for that finding.

> > 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.
> 

Isn't that handled in watchdog_notify_pretimeout with if (!wdd->gov)?
As I understand the code, a governor is registered earliest in
watchdog_register_pretimeout, which is called by watchdog_dev_register.
The same when doing an unregister, which should be called when doing a
watchdog_dev_unregister.

> > 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;".
> 

Thanks, will fix that too. 

Regards,
Stefan