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

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Message-ID: <20140114082632.GA28648@spo001.leaseweb.com>
Date:	Tue, 14 Jan 2014 09:26:32 +0100
From:	Wim Van Sebroeck <wim@...ana.be>
To:	Dave Young <dyoung@...hat.com>
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

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...

Kind regards,
Wim.

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