Re: PPC476 hangs during tlb flush after calling /init in crash kernel with linux 5.4+

From: Christophe Leroy
Date: Tue Apr 27 2021 - 13:26:28 EST

Hi Eddies,

Le 27/04/2021 à 19:03, Eddie James a écrit :
Hi all,

I'm having a problem in simulation and hardware where my PPC476
processor stops executing instructions after callling /init. In my case
this is a bash script. The code descends to flush the TLB, and
somewhere in the loop in _tlbil_pid, the PC goes to
InstructionTLBError47x but does not go any further. This only occurs in
the crash kernel environment, which is using the same kernel,
initramfs, and init script as the main kernel, which executed fine. I
do not see this problem with linux 4.19 or 3.10. I do see it with 5.4
and 5.10. I see a fair amount of refactoring in the PPC memory
management area between 4.19 and 5.4. Can anyone point me in a
direction to debug this further? My stack trace is below as I can run
gdb in simulation.

Can you bisect to pin point the culprit commit ?

Assuming the problem is in arch/powerpc/ , you should get the result in approx 10 steps:

[root@po15610vm linux-powerpc]# git bisect start -- arch/powerpc/
[root@po15610vm linux-powerpc]# git bisect bad v5.4
[root@po15610vm linux-powerpc]# git bisect good v4.19
Bisecting: 964 revisions left to test after this (roughly 10 steps)