linux-kernel - Re: [PATCHv3] watchdog: Add stop_on_reboot parameter to control reboot policy

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Date:   Sun, 23 Feb 2020 06:09:23 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Dmitry Safonov <dima@...sta.com>, linux-kernel@...r.kernel.org
Cc:     Dmitry Safonov <0x7f454c46@...il.com>,
        Wim Van Sebroeck <wim@...ux-watchdog.org>,
        linux-watchdog@...r.kernel.org
Subject: Re: [PATCHv3] watchdog: Add stop_on_reboot parameter to control
 reboot policy

On 2/23/20 3:49 AM, Dmitry Safonov wrote:
> Many watchdog drivers use watchdog_stop_on_reboot() helper in order
> to stop the watchdog on system reboot. Unfortunately, this logic is
> coded in driver's probe function and doesn't allows user to decide what
> to do during shutdown/reboot.
> 
> On the other side, Xen and Qemu watchdog drivers (xen_wdt and i6300esb)
> may be configured to either send NMI or turn off/reboot VM as
> the watchdog action. As the kernel may stuck at any state, sending NMIs
> can't reliably reboot the VM.
> 
> At Arista, we benefited from the following set-up: the emulated watchdogs
> trigger VM reset and softdog is set to catch less severe conditions to
> generate vmcore. Just before reboot watchdog's timeout is increased
> to some good-enough value (3 mins). That keeps watchdog always running
> and guarantees that VM doesn't stuck.
> 
> Provide new stop_on_reboot module parameter to let user control
> watchdog's reboot policy.
> 
> Cc: Guenter Roeck <linux@...ck-us.net>
> Cc: Wim Van Sebroeck <wim@...ux-watchdog.org>
> Cc: linux-watchdog@...r.kernel.org
> Signed-off-by: Dmitry Safonov <dima@...sta.com>

Reviewed-by: Guenter Roeck <linux@...ck-us.net>

> ---
> Changes:
> v3: Make module parameter read-only in runtime (Thanks Guenter for
>      spotting the typo!)
> v2: Add module parameter instead of ioctl()
> 
>   drivers/watchdog/watchdog_core.c | 12 ++++++++++++
>   1 file changed, 12 insertions(+)
> 
> diff --git a/drivers/watchdog/watchdog_core.c b/drivers/watchdog/watchdog_core.c
> index 861daf4f37b2..423844757812 100644
> --- a/drivers/watchdog/watchdog_core.c
> +++ b/drivers/watchdog/watchdog_core.c
> @@ -39,6 +39,10 @@
>   
>   static DEFINE_IDA(watchdog_ida);
>   
> +static int stop_on_reboot = -1;
> +module_param(stop_on_reboot, int, 0444);
> +MODULE_PARM_DESC(stop_on_reboot, "Stop watchdogs on reboot (0=keep watching, 1=stop)");
> +
>   /*
>    * Deferred Registration infrastructure.
>    *
> @@ -254,6 +258,14 @@ static int __watchdog_register_device(struct watchdog_device *wdd)
>   		}
>   	}
>   
> +	/* Module parameter to force watchdog policy on reboot. */
> +	if (stop_on_reboot != -1) {
> +		if (stop_on_reboot)
> +			set_bit(WDOG_STOP_ON_REBOOT, &wdd->status);
> +		else
> +			clear_bit(WDOG_STOP_ON_REBOOT, &wdd->status);
> +	}
> +
>   	if (test_bit(WDOG_STOP_ON_REBOOT, &wdd->status)) {
>   		wdd->reboot_nb.notifier_call = watchdog_reboot_notifier;
>   
>