[poll / rfc] kdb_stop_cpus

Robert N. M. Watson rwatson at FreeBSD.org
Sat Jun 4 09:11:10 UTC 2011

On 4 Jun 2011, at 09:22, Andriy Gapon wrote:

> on 03/06/2011 20:57 Robert N. M. Watson said the following:
>> On 3 Jun 2011, at 16:13, Andriy Gapon wrote:
>>> I wonder if anybody uses kdb_stop_cpus with non-default value. If, yes, I
>>> am very interested to learn about your usecase for it.
>> The issue that prompted the sysctl was non-NMI IPIs being used to enter the
>> debugger or reboot following a core hanging with interrupts disabled. With
>> the switch to NMI IPIs in some of those circumstances, life is better -- at
>> least, on hardware that supports non-maskable IPIs. I seem to recall sparc64
>> doesn't, however?
> Seems to be so as Nathan has also pointed out for PPC.
> For this I also plan the following change:
> commit 458ebd9aca7e91fc6e0825c727c7220ab9f61016
>    generic_stop_cpus: move timeout detection code from under DIAGNOSTIC
>    ... and also increase it a bit.
>    IMO it's better to detect and report the (rather serious) condition and
>    allow a system to proceed somehow rather than be stuck in an endless
>    loop.

Agreed on detecting and reporting. It would be good to confirm that it works in practice, however, and also that there are no false positives. I'm not sure what the best test scenarios are for that.


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