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

[Michael Ellerman]

Jens Axboe <axboe at kernel.dk> writes:
> 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.

Do kthread's ever core dump? I didn't think they did, but I can't find
any logic to prevent it.

Maybe it's always been possible but just never happened due to luck.

As Nick said we should probably have a non-NULL regs for PF_IO_WORKERS,
but I'll still take this as a nice backportable fix for the immediate
crash.

I tagged it as Fixes: pointing back at the commit that added ppr_get(),
even though I don't know for sure the bug was triggerable back then
(v4.8).

cheers