linux-kernel - Re: [PATCH] watchdog: Respect handle_boot_enabled when setting last last_hw

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Date:   Fri, 30 Jul 2021 13:49:52 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Jan Kiszka <jan.kiszka@...mens.com>,
        Wim Van Sebroeck <wim@...ux-watchdog.org>,
        linux-watchdog@...r.kernel.org
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Tero Kristo <t-kristo@...com>
Subject: Re: [PATCH] watchdog: Respect handle_boot_enabled when setting last
 last_hw_keepalive

On 7/30/21 12:39 PM, Jan Kiszka wrote:
> From: Jan Kiszka <jan.kiszka@...mens.com>
> 
> We must not pet a running watchdog when handle_boot_enabled is off
> because this requests to only start doing that via userspace, not during
> probing.
> 

The scope of the changed function is quite limited. See the
definition of watchdog_set_last_hw_keepalive(). On top of that,
__watchdog_ping() does a bit more than just ping the watchdog,
and it only pings the watchdog in limited circumstances. On top of that,
the scope of handle_boot_enabled is different: If enabled, it tells
the watchdog core to keep pinging a watchdog until userspace opens
the device. This is about continuous pings, not about an initial one.
Given that, I'd rather have the watchdog subsystem issue an additional
ping than risking a regression.

The only driver calling watchdog_set_last_hw_keepalive() is rti_wdt.c.
Does this patch solve a specific problem observed with that watchdog ?

Guenter

> Signed-off-by: Jan Kiszka <jan.kiszka@...mens.com>
> ---
>   drivers/watchdog/watchdog_dev.c | 5 ++++-
>   1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/watchdog/watchdog_dev.c b/drivers/watchdog/watchdog_dev.c
> index 3bab32485273..3c93d00bb284 100644
> --- a/drivers/watchdog/watchdog_dev.c
> +++ b/drivers/watchdog/watchdog_dev.c
> @@ -1172,7 +1172,10 @@ int watchdog_set_last_hw_keepalive(struct watchdog_device *wdd,
>   
>   	wd_data->last_hw_keepalive = ktime_sub(now, ms_to_ktime(last_ping_ms));
>   
> -	return __watchdog_ping(wdd);
> +	if (handle_boot_enabled)
> +		return __watchdog_ping(wdd);
> +
> +	return 0;
>   }
>   EXPORT_SYMBOL_GPL(watchdog_set_last_hw_keepalive);
>   
>