linux-kernel - Re: [PATCH] watchdog: core: add option to avoid early handling of watchdog

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Message-ID: <f38c7967-ac56-c188-2232-42544088edd8@roeck-us.net>
Date:   Thu, 11 May 2017 06:47:55 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Sebastian Reichel <sebastian.reichel@...labora.co.uk>,
        Sebastian Reichel <sre@...nel.org>,
        Wim Van Sebroeck <wim@...ana.be>
Cc:     linux-watchdog@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] watchdog: core: add option to avoid early handling of
 watchdog

On 05/11/2017 05:52 AM, Sebastian Reichel wrote:
> On some systems its desirable to have watchdog reboot the system
> when it does not come up fast enough. This adds a kernel parameter
> to disable the auto-update of watchdog before userspace takes over
> and a kernel option to set the default. The info messages were
> added to shorten error searching on misconfigured systems.
>
> Signed-off-by: Sebastian Reichel <sebastian.reichel@...labora.co.uk>
> ---
>  drivers/watchdog/Kconfig        | 11 +++++++++++
>  drivers/watchdog/watchdog_dev.c | 16 ++++++++++++++++
>  2 files changed, 27 insertions(+)
>
> diff --git a/drivers/watchdog/Kconfig b/drivers/watchdog/Kconfig
> index 52a70ee6014f..4e08b2b97941 100644
> --- a/drivers/watchdog/Kconfig
> +++ b/drivers/watchdog/Kconfig
> @@ -46,6 +46,17 @@ config WATCHDOG_NOWAYOUT
>  	  get killed. If you say Y here, the watchdog cannot be stopped once
>  	  it has been started.
>
> +config WATCHDOG_HANDLE_BOOT_ENABLED
> +	bool "Disable watchdog shutdown on close"

Enable ?

> +	default y
> +	help
> +	  The default watchdog behaviour (which you get if you say Y here) is
> +	  to ping watchdog devices, that were enabled before the driver has
> +	  been loaded until control is taken over from userspace using the
> +	  /dev/watchdog file. If you say N here, the kernel will not update
> +	  the watchdog on its own. Thus if your userspace does not start fast
> +	  enough your device will reboot.
> +
>  config WATCHDOG_SYSFS
>  	bool "Read different watchdog information through sysfs"
>  	help
> diff --git a/drivers/watchdog/watchdog_dev.c b/drivers/watchdog/watchdog_dev.c
> index d5d2bbd8f428..5e6d6d4db82f 100644
> --- a/drivers/watchdog/watchdog_dev.c
> +++ b/drivers/watchdog/watchdog_dev.c
> @@ -80,6 +80,9 @@ static struct watchdog_core_data *old_wd_data;
>
>  static struct workqueue_struct *watchdog_wq;
>
> +static bool handle_boot_enabled =
> +	IS_ENABLED(CONFIG_WATCHDOG_HANDLE_BOOT_ENABLED);
> +
>  static inline bool watchdog_need_worker(struct watchdog_device *wdd)
>  {
>  	/* All variables in milli-seconds */
> @@ -956,6 +959,14 @@ static int watchdog_cdev_register(struct watchdog_device *wdd, dev_t devno)
>  	 * and schedule an immediate ping.
>  	 */
>  	if (watchdog_hw_running(wdd)) {
> +		if (!handle_boot_enabled) {
> +			pr_info("watchdog%d running and kernel based pre-userspace handler disabled\n",
> +					wdd->id);
> +			return 0;

I don't like the immediate return here; if some other code is added further below,
it may miss this return. Something like

		if (handle_boot_enabled) {
			// do everything here
		} else {
			// print message
		}

would be better.

> +		}
> +
> +		pr_info("auto-update boot-enabled watchdog%d until userspace takes over\n",
> +					wdd->id);

This message will add a lot of noise. If you really think it is useful please make it
a debug message.

>  		__module_get(wdd->ops->owner);
>  		kref_get(&wd_data->kref);
>  		queue_delayed_work(watchdog_wq, &wd_data->work, 0);
> @@ -1106,3 +1117,8 @@ void __exit watchdog_dev_exit(void)
>  	class_unregister(&watchdog_class);
>  	destroy_workqueue(watchdog_wq);
>  }
> +
> +module_param(handle_boot_enabled, bool, 0444);
> +MODULE_PARM_DESC(handle_boot_enabled,
> +	"Watchdog core auto-updates boot enabled watchdogs before userspace takes over (default="
> +	__MODULE_STRING(IS_ENABLED(CONFIG_WATCHDOG_HANDLE_BOOT_ENABLED)) ")");
>