KASAN debug kernel fails to boot at early stage when CONFIG_SMP=y is set (kernel 6.5-rc5, PowerMac G4 3,6)

Erhard Furtner erhard_f at mailbox.org
Mon Aug 14 05:38:55 AEST 2023

On Fri, 11 Aug 2023 06:45:14 +0000
Christophe Leroy <christophe.leroy at csgroup.eu> wrote:

> Le 11/08/2023 à 01:48, Erhard Furtner a écrit :
> > I wanted to fire up my PowerMac G4 MDD (Dual CPU) with a KASAN debug build of kernel 6.5-rc5 for testing purposes. But the kernel fails to boot at a very early stage. I only get a white screen reading
> > "done
> > found display: /pci at f0000000/ATY,AlteracParent at 10/ATY,Alterac_B at 1, opening..."  
> Can you try with CONFIG_PPC_EARLY_DEBUG and see if you get more 
> information on the screen ?

With CONFIG_PPC_EARLY_DEBUG set booting continues and I get two more lines on a white screen:

[    0.000000] printk: bootconsole [udbg0] enabled
[    0.000000] Total memory = 2048MB; using 4096kB for hash table

Afterwards the G4 freezes.

By chane I found out another interesting thing: This only happens on cold boots.

If I boot the G4 up with another kernel first and boot the SMP KASAN kernel afterwards it just boots up fine too! On further reboots the SMP KASAN kernel keeps booting up normally. Until I turn the machine off - and next time I turn it on the same SMP KASAN kernel fails booting again as described. Strange...

This behaviour however is reproducible. Tried that procedure 15-20 times just to be sure. Hope you can make something out of it.

Attached is a dmesg of a successful SMP KASAM kernel boot attempt when a working kernel was booted first.

Erhard F.
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