Re: [PATCH v2 3/3] powerpc: machine check interrupt is a non-maskable interrupt

[Nicholas Piggin <npiggin@gmail.com>]

On Mon, 8 Oct 2018 17:39:11 +0200
Christophe LEROY <christophe.leroy@c-s.fr> wrote:

> Hi Nick,
> 
> Le 19/07/2017 à 08:59, Nicholas Piggin a écrit :
> > Use nmi_enter similarly to system reset interrupts. This uses NMI
> > printk NMI buffers and turns off various debugging facilities that
> > helps avoid tripping on ourselves or other CPUs.
> > 
> > Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
> > ---
> >   arch/powerpc/kernel/traps.c | 9 ++++++---
> >   1 file changed, 6 insertions(+), 3 deletions(-)
> > 
> > diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
> > index 2849c4f50324..6d31f9d7c333 100644
> > --- a/arch/powerpc/kernel/traps.c
> > +++ b/arch/powerpc/kernel/traps.c
> > @@ -789,8 +789,10 @@ int machine_check_generic(struct pt_regs *regs)
> >   
> >   void machine_check_exception(struct pt_regs *regs)
> >   {
> > -	enum ctx_state prev_state = exception_enter();
> >   	int recover = 0;
> > +	bool nested = in_nmi();
> > +	if (!nested)
> > +		nmi_enter();  
> 
> This alters preempt_count, then when die() is called
> in_interrupt() returns true allthough the trap didn't happen in 
> interrupt, so oops_end() panics for "fatal exception in interrupt" 
> instead of gently sending SIGBUS the faulting app.

Thanks for tracking that down.

> Any idea on how to fix this ?

I would say we have to deliver the sigbus by hand.

    if ((user_mode(regs)))
        _exception(SIGBUS, regs, BUS_MCEERR_AR, regs->nip);
    else
        die("Machine check", regs, SIGBUS);