stop_cpus_hard when multiple CPUs are panicking from an NMI

[Ryan Stone]

On Thu, Nov 15, 2012 at 6:41 PM, Attilio Rao <attilio at freebsd.org> wrote:

> On Thu, Nov 15, 2012 at 10:58 PM, Ryan Stone <rysto32 at gmail.com> wrote:
> > At work we have some custom watchdog hardware that sends an NMI upon
> > expiry.  We've modified the kernel to panic when it receives the watchdog
> > NMI.  I've been trying the "stop_scheduler_on_panic" mode, and I've
> > discovered that when my watchdog expires, the system gets completely
> > wedged.  After some digging, I've discovered is that I have multiple CPUs
> > getting the watchdog NMI and trying to panic concurrently.  One of the
> CPUs
> > wins, and the rest spin forever in this code:
>
> Quick question: can you control the way your watchdog sends the NMI?
> Like only to BSP rather than broadcast, etc.
> This is tied to the very unique situation that you cannot really
> deliver the (second) NMI.
>
> Attilio
>
>
> --
> Peace can only be achieved by understanding - A. Einstein
>

I don't believe that I can, but I can check.  In any case I can imagine
other places where this could be an issue.  hwpmc works with NMIs, right?
So an hwpmc bug could trigger the same kind of issues if two CPUs that
concurrently called pmc_intr both tripped over the sane bug.