linux-kernel - RE: [EXTERNAL] Re: [PATCH v4 1/2] watchdog: Add a new flag WDIOF_STOP

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Message-ID:
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Date: Thu, 6 Mar 2025 12:18:20 +0000
From: George Cherian <gcherian@...vell.com>
To: Guenter Roeck <linux@...ck-us.net>, Ahmad Fatoum <a.fatoum@...gutronix.de>
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        Marek Behún
	<kabel@...nel.org>
Subject: RE: [EXTERNAL] Re: [PATCH v4 1/2] watchdog: Add a new flag
 WDIOF_STOP_MAYSLEEP

Hi Guenter,

I am summarizing the topics we discussed in multiple threads here.

>>On 3/5/25 03:01, Ahmad Fatoum wrote:
>> Hi George,
>> Hi Guenter,
>> 
>> On 05.03.25 11:34, George Cherian wrote:
>>>> why is armada_37xx_wdt also here?
>>>> The stop function in that driver may not sleep.
>>> Marek,
>>>
>>> Thanks for reviewing.
>>> Since the stop function has a regmap_write(), I thought it might sleep.
>>> Now that you pointed it out, I assume that it is an MMIO based regmap being used for armada.
>>> I will update the same in the next version
>> 
>> Failure to add WDIOF_STOP_MAYSLEEP when it's needed can lead to
>> kernel hanging. Failure to add an alternative WDIOF_STOP_ATOMIC
>> would lead to the kernel option being a no-op.
>> 
>> I think a no-op stop_on_panic (or reset_on_panic) is a saner default.
>> 
>
>Agreed. Also, I like WDIOF_STOP_ATOMIC more than the WDIOF_STOP_NOSLEEP
>I had suggested in my other response.

1. Instead of blacklisting drivers as WDIOF_STOP_MAYSLEEP, the option will an opt-in.
2. This may not be WDIOF_STOP_AOMIC, instead would be a generic flag not limited to STOP
    operation. May be WDIOF_OPS_ATOMIC (OPS include - .start, .stop, .set_timeout, .ping)
3. Remove the kernel command line option (stop_on_panic) and have a generic reset_on_panic.
4. reset_on_panic=60 (by default )  meaning on a panic the wdog timeout is updated to 60sec
     or the clamp_t(reset_on_panic, min, max_hw_heartbeat_ms).
5. if reset_on_panic=0, it means the watchdog is stopped on panic.
6. All of these to be done by default from panic handler incase of a configured kdump kernel.

-George

>
>Thanks,
>Guenter