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Date: Wed, 25 Oct 2017 23:56:48 +1100
From: Balbir Singh <bsingharora@gmail.com>
To: Michael Neuling <mikey@neuling.org>
Cc: mpe@ellerman.id.au, Vipin K Parashar <vipin@linux.vnet.ibm.com>, Mahesh
 Salgaonkar <mahesh@linux.vnet.ibm.com>, linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH] powernv: Avoid checkstop on HMI and MCE
Message-ID: <20171025235648.1152bff3@MiWiFi-R3-srv>
In-Reply-To: <20171024092005.3861-1-mikey@neuling.org>
References: <20171024092005.3861-1-mikey@neuling.org>
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On Tue, 24 Oct 2017 20:20:05 +1100
Michael Neuling <mikey@neuling.org> wrote:

> On an unrecoverable HMI or MCE only generate an checkstop (via
> PLATFORM ERROR opal reboot call) when panic_on_oops is set.
> 
> We currently generate an checkstop as an attempt for the FSP to grab a
> dump and then reboot us. Unfortunately this never works and no one
> I've talked to has ever seen a resulting dump, let alone got useful
> information from it.
> 
> Even worse, the checkstop gets in the way of debugging real
> problems. If we hit a software bug that results in this, we get no
> opportunity to debug it live. Similarly if the bug is due to hardware
> that is not in the dump (say PCI or NVLINK GPU), we get no information
> in the dump about that hardware.
> 
> So let's remove it unless someone sets panic_on_oops.
> 
> Signed-off-by: Michael Neuling <mikey@neuling.org>
> ---
>  arch/powerpc/platforms/powernv/opal-hmi.c | 6 ++++++
>  arch/powerpc/platforms/powernv/opal.c     | 4 ++++
>  2 files changed, 10 insertions(+)
> 
> diff --git a/arch/powerpc/platforms/powernv/opal-hmi.c b/arch/powerpc/platforms/powernv/opal-hmi.c
> index c9e1a4ff29..23780970d0 100644
> --- a/arch/powerpc/platforms/powernv/opal-hmi.c
> +++ b/arch/powerpc/platforms/powernv/opal-hmi.c
> @@ -29,6 +29,7 @@
>  #include <asm/opal.h>
>  #include <asm/cputable.h>
>  #include <asm/machdep.h>
> +#include <asm/bug.h>
>  
>  #include "powernv.h"
>  
> @@ -284,6 +285,11 @@ static void hmi_event_handler(struct work_struct *work)
>  			print_hmi_event_info(hmi_evt);
>  		}
>  
> +		if (!panic_on_oops) {
> +			die("Unrecoverable HMI exception", NULL, SIGBUS);
> +			return;
> +		}
> +

If panic_on_oops is set, we checkstop, not panic! Passing NULL to die, will
cause arch_uprobe_exception_notify() to complain.

We could respin this a bit and I can send an updated patch if there is interest


Balbir Singh.