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