linux-kernel - Re: [REGRESSION] mainline boot regression on AMD Stoney Ridge Chromebooks

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Date: Wed, 10 Apr 2024 21:34:33 +0200
From: Thomas Gleixner <tglx@...utronix.de>
To: Laura Nao <laura.nao@...labora.com>
Cc: kernel@...labora.com, laura.nao@...labora.com,
 linux-kernel@...r.kernel.org, regressions@...mhuis.info,
 regressions@...ts.linux.dev, x86@...nel.org
Subject: Re: [REGRESSION] mainline boot regression on AMD Stoney Ridge
 Chromebooks

Laura!

On Wed, Apr 10 2024 at 18:11, Laura Nao wrote:
> On 4/10/24 15:57, Thomas Gleixner wrote:
>> I just moved the exit check a bit so we should see the scan info. That
>> should tell me what goes south.
>
> Here's the full kernel log with the latest patch applied: 
> https://pastebin.com/raw/r2CkP396

Ok. Now I can see it.

	pr_info("NPP %u\n", tscan.amd_nodes_per_pkg);

The output is:

<6>[    0.000000] NPP 3

The original code then reads out 1, which is what's expected on that
machine.

Now that bogus value '3' is used later in

    a %= b / 3

as b == 2, the division result is zero, which makes the %= operation
crash with a division by zero. As there are no handlers yet, nothing to
see.

The problem causing the bogus readout sits between my keyboard and my
chair.

I'll send out the fixes with proper change logs later tonight.

Thanks for all your help!

       tglx