IPMI hardware watchdogs Re: dell r420/r320 stable/9

[Andriy Gapon]

on 27/07/2012 17:33 Andrew Boyer said the following:
> 
> On Jul 26, 2012, at 8:50 PM, Sean Bruno wrote:
> 
>> For the time being I had to revert the following from my stable/9 tree. 
>> Otherwise I would get a kernel panic on shutdown from ipmi(4).
>> 
>> http://svnweb.freebsd.org/base?view=revision&revision=237839 
>> http://svnweb.freebsd.org/base?view=revision&revision=221121
>> 
> 
> 
> On a somewhat related note: We noticed recently that you can't pet or disable
> the IPMI hardware watchdog once SCHEDULER_STOPPED() is true.  This means it
> can fire unexpectedly while you're dumping core or rebooting, depending on
> how long the timeout was on the pet before the panic.  The ipmi driver will
> need to process the command differently if the scheduler is stopped.  I
> haven't had time to look at a fix yet.

Yeah, I noticed that unlike most (all?) other watchdog drivers where watchdog
re-arming is a very basic operation like doing one I/O the IPMI watchdog does
some more complex stuff which involves waiting on another thread.  I think that
this may be a little bit too much for a reliable watchdog driver.  At least, as
you note, this definitely won't work for the panic case where only one thread is
left running.  I guess that the driver should check for that case and do a
direct operation instead of enqueueing a request and waiting for another thread
to execute it.

-- 
Andriy Gapon