obtaining a minidump from panic() called from NMI handler

[Maksim Yevmenkin]

Andriy,

>> i have a question about obtaining minidump as result of panic() being
>> called from nmi handler. basically, i have a way to trigger nmi, and,
>> i would like to panic() system and obtain a minidump.
>>
>> i have modified isa_nmi() to appropriately inspect bits and return
>> non-zero return code. i have turned off machdep.kdb_on_nmi knob (set
>> it to zero). i have confirmed that amd64 trap() is called with correct
>> T_NMI type. i've also confirmed that panic() is called from amd64's
>> trap().
>>
>> the issue i have is that system is rebooting too early. basically, it
>> looks like minidump is started, but, for whatever reason, other cpus
>> are not completely stopped (or may be they are panic()ing again) and
>> system just reboots without having complete the minidump.
>>
>> the issue is not present when machdep.kdb_on_nmi is set to 1. in this
>> case, system drops into ddb prompt and 'call doadump' works as
>> expected. for various reasons i can not use ddb, and, would like to
>> have system save nmi triggered minidump completely unattended.
>>
>> can someone please give me a clue as to what i should be looking into
>> to make this work?
>
> could it be that more than one CPUs get the NMI at the same time?

i guess, its possible. is there an easy way to check for that?

> IF yes, then the current code wouldn't handle that well - each of the NMI-ed
> CPUs will try to stop all others with another NMI and it will wait until each of
> those CPUs sets an acknowledgement bit in its NMI handler.  This scheme works
> fine if there's only one CPU that wants to become the master, but results in a
> deadlock otherwise.

that makes sense. i don't observe deadlock, but, simple reboot.

thanks,
max