Freeze on ppc32 MPC8248 board with 5.2 kernel

Freeze on ppc32 MPC8248 board with 5.2 kernel

[Doug Crawford]

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We have a ppc32 MPC8248 board that is working perfectly with the 4.19
kernel.
We have noticed two issues with the 5.2 kernel:

1) If the new CONFIG_PPC_KUAP (kernel userspace access protection) is
enabled the kernel freezes right after initializing all the drivers and
just before starting /sbin/init.

2) If CONFIG_PPC_KUAP is disabled the system starts up, but any user space
program will hang indefinitely after calling the GCC atomic
"__sync_bool_compare_and_swap".  This happens when nginx starts.  The same
nginx binary works fine on a 4.19 kernel.

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Re: Freeze on ppc32 MPC8248 board with 5.2 kernel

[Christophe Leroy]

Hi Doug,

Le 26/07/2019 à 00:30, Doug Crawford a écrit :
> We have a ppc32 MPC8248 board that is working perfectly with the 4.19 
> kernel.
> We have noticed two issues with the 5.2 kernel:

  Have you tried 5.0 and 5.1 ?

> 
> 1) If the new CONFIG_PPC_KUAP (kernel userspace access protection) is 
> enabled the kernel freezes right after initializing all the drivers and 
> just before starting /sbin/init.

Can you provide your .config ?

Can you also provide the output of the boot console ?

> 
> 2) If CONFIG_PPC_KUAP is disabled the system starts up, but any user 
> space program will hang indefinitely after calling the GCC atomic 
> "__sync_bool_compare_and_swap".  This happens when nginx starts.  The 
> same nginx binary works fine on a 4.19 kernel.

Can you provide 'dmesg' ?

What version of GCC do you use ?

Have you tried a simple program doing nothing else than 
__sync_bool_compare_and_swap() ?

Can you provide a disassembly of the function that uses 
__sync_bool_compare_and_swap() ?

Thanks
Christophe