linux-kernel - Re: [PATCH] watchdog: add a parameter for stop wdt before register

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Date:	Tue, 14 Jan 2014 16:41:54 +0800
From:	Dave Young <dyoung@...hat.com>
To:	Wim Van Sebroeck <wim@...ana.be>
Cc:	dzickus@...hat.com, bhe@...hat.com, vgoyal@...hat.com,
	linux-watchdog@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] watchdog: add a parameter for stop wdt before register

On 01/14/14 at 09:26am, Wim Van Sebroeck wrote:
> Hi Dave,
> 
> > In kdump kernel watchdog could interrupt vmcore capturing because we
> > have no way to disable/stop it while crashing happens.
> > 
> > Add a module parameter stop_before_register so watchdog can be stopped
> > before register in driver loading path. Thus we can try to load the
> > watchdog driver as early as possible in kdump kernel to ensure vmcore
> > capturing.
> > 
> > Don Zickus mentioned that there's the case that bios start the watchdog
> > and it is expected that the kernel keep the watchdog alive. To address
> > this case I added the module parameter which is false by default so
> > it will stop the watchdog only when user provice kernel cmdline
> > "watchdog.stop_before_register=1".  
> > 
> > Signed-off-by: Dave Young <dyoung@...hat.com>
> > ---
> >  drivers/watchdog/watchdog_core.c |    6 ++++++
> >  1 file changed, 6 insertions(+)
> > 
> > --- linux.orig/drivers/watchdog/watchdog_core.c
> > +++ linux/drivers/watchdog/watchdog_core.c
> > @@ -42,6 +42,7 @@
> >  
> >  static DEFINE_IDA(watchdog_ida);
> >  static struct class *watchdog_class;
> > +static bool stop_before_register;
> >  
> >  static void watchdog_check_min_max_timeout(struct watchdog_device *wdd)
> >  {
> > @@ -119,6 +120,9 @@ int watchdog_register_device(struct watc
> >  	if (wdd->ops->start == NULL || wdd->ops->stop == NULL)
> >  		return -EINVAL;
> >  
> > +	if (stop_before_register)
> > +		wdd->ops->stop(wdd);
> > +
> >  	watchdog_check_min_max_timeout(wdd);
> >  
> >  	/*
> > @@ -220,6 +224,8 @@ static void __exit watchdog_exit(void)
> >  subsys_initcall(watchdog_init);
> >  module_exit(watchdog_exit);
> >  
> > +module_param(stop_before_register, bool, 0644);
> > +
> >  MODULE_AUTHOR("Alan Cox <alan@...rguk.ukuu.org.uk>");
> >  MODULE_AUTHOR("Wim Van Sebroeck <wim@...ana.be>");
> >  MODULE_DESCRIPTION("WatchDog Timer Driver Core");
> 
> Hmm, need to look closer to this, but my first thought is:
> what about devices that cannot be stopped once started...
> They should be able to override this module_parameter...

Hi, Wim

Thanks for quick feedback!

I'm not sure the meaning of "cannot be stopped", if it means that
the policy that it should not be stopped, I think since the watchdog_core
is always built-in so the param can only be provided via boot cmdline it would
be fine?

For device which really *cannot* stop, the stop() will fail silently?

Thanks
Dave
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