Re: [PATCH 1/3] watchdog: realtek-otto: Change to use regmap API

[Rustam Adilov <adilov@disroot.org>]

On 2026-05-09 17:16, sashiko-bot@kernel.org wrote:
> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [High] Deadlock risk in the atomic restart handler due to regmap's internal spinlock.
> --
> 
> commit a520c8e2203154ba331a6ae28f00daec074e62ee
> Author: Rustam Adilov <adilov@disroot.org>
> 
> watchdog: realtek-otto: Change to use regmap API
> 
> This commit converts the realtek-otto watchdog driver to use the regmap API
> instead of direct mmio accesses. It replaces direct read/modify/write
> sequences with regmap functions and selects REGMAP_MMIO.
> 
>> diff --git a/drivers/watchdog/realtek_otto_wdt.c b/drivers/watchdog/realtek_otto_wdt.c
>> index 2c30ddd574c59..e5e9cb480f4f9 100644
>> --- a/drivers/watchdog/realtek_otto_wdt.c
>> +++ b/drivers/watchdog/realtek_otto_wdt.c
> [ ... ]
>> @@ -199,7 +189,7 @@ static int otto_wdt_restart(struct watchdog_device *wdev, unsigned long reboot_m
>>  
>>  	/* Configure for shortest timeout and wait for reset to occur */
>>  	v = FIELD_PREP(OTTO_WDT_CTRL_RST_MODE, reset_mode) | OTTO_WDT_CTRL_ENABLE;
>> -	iowrite32(v, ctrl->base + OTTO_WDT_REG_CTRL);
>> +	regmap_write(ctrl->regmap, OTTO_WDT_REG_CTRL, v);
> 
> Could this regmap_write() cause a deadlock during system restart?
> 
> The restart handler is often called during system shutdown or kernel panic
> in an atomic context with local interrupts disabled. Since
> devm_regmap_init_mmio() configures the regmap to use a spinlock by default,
> if a panic occurs while another cpu holds the regmap lock (e.g., during
> a ping or timeout update) and that cpu is halted by smp_send_stop(), this
> regmap_write() could spin endlessly and prevent the system from rebooting.
> 
> Additionally, on preempt-rt kernels, the regmap spinlock becomes a sleepable
> rt_mutex, which could cause a sleeping in atomic context bug when acquired
> with interrupts disabled.
> 
>>  	mdelay(3 * otto_wdt_tick_ms(ctrl, 0));
>>

Hi Sander,

I hope it is alright if i CCd you for this as i am not an expert on watchdog stuff.
Wonna make sure this issue applies here before i proceed with the suggested solution
to add .disable_locking to regmap_config without understanding the consequences of it.

Best,
Rustam