kernel since 5.6 do not boot anymore on Apple PowerBook

[Christophe Leroy]

Hello Giuseppe,

Le 22/08/2020 à 10:28, Giuseppe Sacco a écrit :
> Hello Christophe,
> 
> Il giorno ven, 21/08/2020 alle 16.03 +0200, Christophe Leroy ha
> scritto:
> [...]
>>
>> You also said in a previous mail that your original issue also
>> happens
>> when CONFIG_VMAP_STACK is not selected. The above bug being linked
>> to
>> CONFIG_VMAP_STACK, maybe it would be easier to bisect with
>> CONFIG_VMAP_STACK unselected.
> 
> I was wrong. Disabling CONFIG_VMAP_STACK led me to all "good" compile
> and bisect ended without finding the culprit commit.
> 
> So, I started from scratch: I rebuilt HEAD and found that it does show
> the original problem I am facing, then I rebuilt it without
> CONFIG_VMAP_STACK and found that it does pass (fix?) the problem, since
> kernel continue booting, but then it stops with three Oops related to
> command systemd-udevd.
> 
> You may find a video that displays the complete boot, vmlinux, config,
> and system.map files here:
> 

The Oopses in the video are fixed in 5.9-rc2, see my response to your 
other mail.

So now we know that your kernel doesn't boot when CONFIG_VMAP_STACK is set.
Can you remind the exact problem ?

One common problem with CONFIG_VMAP_STACK is when some drivers are 
invalidly using buffers in stack for DMA.

Couldn't try with CONFIG_DEBUG_VIRTUAL (without CONFIG_VMAP_STACK) and 
see if it triggers some warnings ?

Thanks
Christophe