G5 Quad hangs early on 4.20.2 / 5.0-rc2+

[Michael Ellerman]

Tobias Ulmer <tobiasu at tmux.org> writes:
> 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.

Can you try:

58cfbac25b1f ("Revert "selftests/powerpc: Fix out-of-tree build errors"")

If that's bad and v4.19 is good that would isolate it to about 222
commits.

cheers