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Date: Thu, 10 Nov 2016 15:24:59 +1100
From: Nicholas Piggin <npiggin@gmail.com>
To: Michael Ellerman <mpe@ellerman.id.au>
Cc: linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH 1/2] powerpc: fix graceful debugger recovery
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On Thu, 10 Nov 2016 12:35:59 +1100
Michael Ellerman <mpe@ellerman.id.au> wrote:

> Nicholas Piggin <npiggin@gmail.com> writes:
> 
> > 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!

> 
> > 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