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Subject: Re: PPC476 hangs during tlb flush after calling /init in crash kernel
 with linux 5.4+
To:     Eddie James <eajames@linux.ibm.com>, linuxppc-dev@lists.ozlabs.org
Cc:     linux-kernel@vger.kernel.org, benh@kernel.crashing.org,
        paulus@samba.org, mpe@ellerman.id.au, npiggin@gmail.com,
        miltonm@us.ibm.com
References: <b973fa4768140021719e7cc3123ee873d8b2a3f1.camel@linux.ibm.com>
From:   Christophe Leroy <christophe.leroy@csgroup.eu>
Message-ID: <a24e9e0d-1d4f-506b-9303-4b995815d3c4@csgroup.eu>
Date:   Tue, 27 Apr 2021 19:26:07 +0200
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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)


Christophe