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[PATCH] watchdog: core: add option to avoid early handling of watchdog

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  [PATCH] watchdog: core: add option to avoid early handling of watchdog Sebastian Reichel <sebastian.reichel@collabora.co.uk> - 2017-05-11 15:00 +0200
    Re: [PATCH] watchdog: core: add option to avoid early handling of  watchdog Guenter Roeck <linux@roeck-us.net> - 2017-05-11 15:50 +0200

#1639375 — [PATCH] watchdog: core: add option to avoid early handling of watchdog

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@collabora.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"
+	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;
+		}
+
+		pr_info("auto-update boot-enabled watchdog%d until userspace takes over\n",
+					wdd->id);
 		__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)) ")");
-- 
2.11.0

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#1639455 — 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@collabora.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)) ")");
>

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