Re: [PATCH v9 0/3] watchdog: allow setting deadline for opening /dev/watchdogN

[Jerry Hoemann]

On Mon, Jan 21, 2019 at 08:45:38PM +0000, Rasmus Villemoes wrote:
> If a watchdog driver tells the framework that the device is running,
> the framework takes care of feeding the watchdog until userspace opens
> the device. If the userspace application which is supposed to do that
> never comes up properly, the watchdog is fed indefinitely by the
> kernel. This can be especially problematic for embedded devices.
> 
> The existing handle_boot_enabled cmdline parameter/config option
> partially solves that, but that is only usable for the subset of
> hardware watchdogs that have (or can be configured by the bootloader
> to have) a timeout that is sufficient to make it realistic for
> userspace to come up. Many devices have timeouts of only a few
> seconds, or even less, making handle_boot_enabled insufficient.
> 
> These patches allow one to set a maximum time for which the kernel
> will feed the watchdog, thus ensuring that either userspace has come
> up, or the board gets reset. This allows fallback logic in the
> bootloader to attempt some recovery (for example, if an automatic
> update is in progress, it could roll back to the previous version).
> 

Rasmus,

Sorry if I missed it, but are you still looking into adding
this feature?  I was thinking it might also be useful with
kdump when a watchdog was running in the first kernel.

After a panic if kdump is configured, the system will boot the
crash kernel.  If a watchdog was running in the first kernel
it would still running in the crash kernel environment.

Some of the drivers on HPE systems take a non-trivial amount of time
to reset during the crash kernel boot, so it would be good to have
the core pet the watchdog until user space is ready.  But as the
crash kernel environment has its issues,  we really don't want
the core to ping the watchdog indefinitely.

Thanks

Jerry

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Jerry Hoemann                  Software Engineer   Hewlett Packard Enterprise
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