[BUG][next-20170619][347de24] PowerPC boot fails with Oops

[Nicholas Piggin]

On Tue, 20 Jun 2017 12:49:25 +0530
Abdul Haleem <abdhalee at linux.vnet.ibm.com> wrote:

> Hi,
> 
> commit: 347de24 (powerpc/64s: implement arch-specific hardlockup
> watchdog)
> 
> linux-next fails to boot on PowerPC Bare-metal box.
> 
> Test: boot
> Machine type: Power 8 Bare-metal
> Kernel: 4.12.0-rc5-next-20170619
> gcc: version 4.8.5
> 
> 
> In file arch/powerpc/kernel/watchdog.c
> 
> void soft_nmi_interrupt(struct pt_regs *regs)
> {
>     unsigned long flags;
>     int cpu = raw_smp_processor_id();
>     u64 tb;
> 
>     if (!cpumask_test_cpu(cpu, &wd_cpus_enabled))
>         return;
> 
> >>> nmi_enter();  

Thanks for the report.

This is due to emergency stacks not zeroing preempt_count, so they get
garbage here, and it just trips the BUG_ON(in_nmi()) check.

Don't think it's a bug in the proposed new powerpc watchdog. (at least
I was able to reproduce your bug and fix it by fixing the stack init).

Thanks,
Nick