Hi Guenter,

On 24 May 2015 at 04:01, Guenter Roeck [off-list ref] wrote:

On 05/23/2015 12:40 PM, Timur Tabi wrote:
[ ... ]

quoted

I use emergency_restart(), because the watchdog-api.txt documentation says
this:

"If userspace fails (RAM error, kernel bug, whatever), the
notifications cease to occur, and the hardware watchdog will reset the
system (causing a reboot) after the timeout occurs."

Maybe I'm reading this too literally, but to me this means that when the
timeout expires, the system has to reset immediately.

However, maybe panic() is better, since it can do the same thing and more.

I have a specific requirement at work to have watchdog expiration
(not this watchdog, this is different HW) result in a panic, specifically
to enable crashdump support and thus post-mortem analysis.

I had not thought about this use case myself, and I had always wondered
why watchdog driver implementers would choose to call panic() after an
interrupt or NMI. But we live and learn, so now I finally understand.

In the pretimeout/timeout world, the pretimeout would (typically)
result in a panic, and the timeout would result in a reset. So one
would set the timer register to 10s for 10s pretimeout and 20s timeout.

However, the pretimeout concept assumes that there are two timers
which can be set independently. As you had pointed out earlier,
and as the specification seems to confirm, that is not the case here.

Sorry, in Documentation/watchdog/watchdog-api.txt, I can not get the
info about " the pretimeout concept assumes that there are two timers
which can be set independently."
Could you kindly point out where is the assumption.

I thinks in kernel documentation,  that meams "one watchdog has two
timeout stages", maybe I miss something. Could you help me out?

As such, I don't really understand why and how the pretimeout / timeout
concept would add any value here and not just make things more
complicated than necessary. Maybe I am just missing something.

If pretimeout concept assumes that there are two timers, I
misunderstand the "pretimeout", then I will delete the pretimeout
immediately.

Thanks,
Guenter

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Best regards,

Fu Wei
Software Engineer
Red Hat Software (Beijing) Co.,Ltd.Shanghai Branch
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