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

[Christophe LEROY]

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 at 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.

Any idea on how to fix this ?

Christophe

>   
>   	__this_cpu_inc(irq_stat.mce_exceptions);
>   
> @@ -820,10 +822,11 @@ void machine_check_exception(struct pt_regs *regs)
>   
>   	/* Must die if the interrupt is not recoverable */
>   	if (!(regs->msr & MSR_RI))
> -		panic("Unrecoverable Machine check");
> +		nmi_panic(regs, "Unrecoverable Machine check");
>   
>   bail:
> -	exception_exit(prev_state);
> +	if (!nested)
> +		nmi_exit();
>   }
>   
>   void SMIException(struct pt_regs *regs)
>