[PATCH] powerpc: don't try to copy ppc for task with NULL pt_regs

[Michael Ellerman]

"Nicholas Piggin" <npiggin at gmail.com> writes:
> On Mon Mar 27, 2023 at 8:15 AM AEST, Jens Axboe wrote:
>> Powerpc sets up PF_KTHREAD and PF_IO_WORKER with a NULL pt_regs, which
>> from my (arguably very short) checking is not commonly done for other
>> archs. This is fine, except when PF_IO_WORKER's have been created and
>> the task does something that causes a coredump to be generated. Then we
>> get this crash:
>
> Hey Jens,
>
> Thanks for the testing and the patch.
>
> I think your patch would work, but I'd be inclined to give the IO worker
> a pt_regs so it looks more like other archs and a regular user thread.
>
> Your IO worker bug reminded me to resurrect some copy_thread patches I
> had and I think they should do that
>
> https://lists.ozlabs.org/pipermail/linuxppc-dev/2023-March/256271.html
>
> I wouldn't ask you to test it until I've at least tried, do you have a
> test case that triggers this?

I hit it once on one machine while running the mtr test from the other
thread. I'm not sure what leads to it failing that way rather than the
usual case of the mariadb test just printing an error.

I've got your series applied and am testing it now.

cheers