G5 Quad hangs early on 4.20.2 / 5.0-rc2+

[Tobias Ulmer]

On Wed, Jan 16, 2019 at 12:15:14PM +1100, Benjamin Herrenschmidt wrote:
> On Tue, 2019-01-15 at 23:49 +0100, Tobias Ulmer wrote:
> > Hi,
> > 
> > both the latest stable 4.20.2 and 5.0 rc2+ hang early on the G5 Quad.
> > 
> > Surely I'm not the first to run into this, but I couldn't find any
> > discussion or bug report. Sorry if you're already aware.
> > 
> > You can see it hang here (5.0 rc2+, 4.20.2 is nearly identical) until
> > the watchdog triggers a reboot:
> > 
> > https://i.imgur.com/UiCVRuG.jpg
> > 
> > If I had to make an uneducated guess, it seems to boot into the same
> > codepath twice (mpic was already initialized, then it starts again right
> > after smp bringup). Maybe on a second CPU?
> > 
> > To narrow it down a little, my last known good was 4.18.9
> 
> I don't think it's an MPIC related problem but it does appear to hang
> about when interrupts get turned on.

When they get turned on for the second time, for some reason. You can see the
end of the first time just on top of the screen.

It repeats part of the startup initialization right after it's done with
smp bringup.

> 
> I have one of these critters in the office, but I'm working remotely
> this week so I won't be able to dig into this until next week.
> 
> It might help if you could bisect in the meantime.

I'm bisecting it now, but it's slow going since I don't have much time
to babysit the machine. The problem shows up somewhere between v4.19 and
v4.20.

> 
> Cheers,
> Ben.
> 
>