Re: [PATCH 1/2] powerpc: fix graceful debugger recovery

On Thu, 10 Nov 2016 12:35:59 +1100
Michael Ellerman [off-list ref] wrote:

Nicholas Piggin [off-list ref] writes:

quoted

When exiting xmon with 'x' (exit and recover), oops_begin bails
out immediately, but die then calls __die() and oops_end(), which
cause a lot of bad things to happen.  

In fact oops_begin() returns 1, which oops_end() then passes directly to
raw_local_irq_restore() as flags. On 64-bit that actually works because
arch_local_irq_restore() takes just "en" (enable), not real flags. But
on 32-bit it's supposed to be the MSR value. So that's impressively
broken.

Yeah, I guess most of the time you either go to debugger with
sysrq, or in case of a crash don't try to graceful recover.

When sending debug NMIs down via system reset it becomes a problem!

quoted

If the debugger was attached then went to graceful recovery, exit
from die() immediately.  

Right. Crucially it doesn't change anything in terms of the actual logic
of oops_begin(), ie. previously oops_begin() did nothing prior to
calling debugger(), and after this patch that remains the same (which
you did mention above but just spelling it out for myself).

Right.

Thanks,
Nick