Re: [PATCH v2] watchdog: mtk_wdt: Stop a running watchdog over system sleep even if not opened

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] watchdog: system reset during suspend_freeze_processes() due to prematurely stopped ping worker
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commit 49206fab5f9c9b345c52cba7a65df971c5a0d992
Author: zoan37 <agentzoan@gmail.com>
Subject: watchdog: mtk_wdt: Stop a running watchdog over system sleep even if not opened

This patch modifies the MTK watchdog driver to stop and restart a watchdog
that was left running by the bootloader across system sleep. It also uses
watchdog_stop_ping_on_suspend() to prevent the core's ping worker from
feeding the watchdog during suspend.

Link: https://lore.kernel.org/all/20261011004322.1118027-1-agentzoan@gmail.com/

> diff --git a/drivers/watchdog/mtk_wdt.c b/drivers/watchdog/mtk_wdt.c
> index 1630ab65d5932..3c493a470b37a 100644
> --- a/drivers/watchdog/mtk_wdt.c
> +++ b/drivers/watchdog/mtk_wdt.c
> @@ -543,6 +543,7 @@ static int mtk_wdt_probe(struct platform_device *pdev)
>  	mtk_wdt_init(&mtk_wdt->wdt_dev);
>  
>  	watchdog_stop_on_reboot(&mtk_wdt->wdt_dev);
> +	watchdog_stop_ping_on_suspend(&mtk_wdt->wdt_dev);

[Severity: High]
Could stopping the ping worker at PM_SUSPEND_PREPARE cause a premature
system reset during process freezing?

By opting in with watchdog_stop_ping_on_suspend(), the core's PM notifier
handles PM_SUSPEND_PREPARE by completely canceling the background ping worker:

drivers/watchdog/watchdog_dev.c:watchdog_dev_suspend() {
    ...
    if (test_bit(WDOG_NO_PING_ON_SUSPEND, &wdd->status)) {
        ...
        kthread_cancel_work_sync(&wd_data->work);
    }
}

Immediately following the PM_SUSPEND_PREPARE notifiers, the suspend core
freezes user-space processes:

kernel/power/suspend.c:suspend_prepare() {
    ...
    error = suspend_freeze_processes();
}

Because freezing tasks and syncing filesystems can routinely block for
several seconds, if the hardware watchdog is initialized with a short
timeout (e.g., 2 seconds via a module parameter), could the hardware
timer expire and hard-reset the board before the device's actual suspend
callback (mtk_wdt_suspend) is ever reached?

Prior to this patch, the unfreezable watchdog_kworker would continue to
feed the hardware during this variable freezing delay.

>  	err = devm_watchdog_register_device(dev, &mtk_wdt->wdt_dev);
>  	if (unlikely(err))
>  		return err;

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261011011536.1139162-1-agentzoan@gmail.com?part=1