Re: [patch V2 22/29] lockup_detector: Make watchdog_nmi_reconfigure() two stage

On Tue, 3 Oct 2017, Michael Ellerman wrote:

Thomas Gleixner [off-list ref] writes:

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The first call is new because previously watchdog_nmi_reconfigure()
wasn't called from softlockup_reconfigure_threads().

Hmm, don't you have the same problem with CPU hotplug or do you just get
lucky because the hotplug callback in your code is ordered vs. the
softlockup thread hotplug callback in a way that this does not hit?

I don't see it with CPU hotplug.

AFAICS that's because softlockup_reconfigure_threads() isn't called for
CPU hotplug. Unless there's a path I'm missing?

As I said in the other reply, I assumed that its called via
watchdog_nmi_enable(cpu), but that's a weak function which is not
implemented on power. So no issue.

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I'm not sure what the easiest fix is. One option would be to just drop
the WARN_ON, it's just there for paranoia AFAICS.

The straight forward way is to make use of the new probe function. Patch
below.

Hmm, I tried that patch, it makes the warning go away. But then I
triggered a deliberate hard lockup and got nothing.

Then I went back to the existing code (in linux-next), and I still get
no warning from a deliberate hard lockup.

So seems there may be some more gremlins. Will test more in the morning.

Hrm. That's weird. I'll have a look and send a proper patch series on top
of next.

Thanks,

	tglx