Re: [PATCH 1/3] powerpc: do not call ppc_md.panic in panic notifier if fadump not used

[Mahesh Jagannath Salgaonkar <mahesh@linux.vnet.ibm.com>]

On 07/04/2017 03:39 PM, Nicholas Piggin wrote:
> If fadump is not registered, and no other crash or debug handlers are
> registered, the powerpc panic handler stops the guest before the generic
> panic code can push out debug information to the console.
> 
> Without this patch, system reset injection to a guest causes the guest to
> silently stop. Afterwards, we get the expected oops trace.
> 
> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
> ---
>  arch/powerpc/kernel/setup-common.c | 15 +++++++++------
>  1 file changed, 9 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/setup-common.c b/arch/powerpc/kernel/setup-common.c
> index 94a948207cd2..39ba09965b04 100644
> --- a/arch/powerpc/kernel/setup-common.c
> +++ b/arch/powerpc/kernel/setup-common.c
> @@ -707,12 +707,15 @@ EXPORT_SYMBOL(check_legacy_ioport);
>  static int ppc_panic_event(struct notifier_block *this,
>                               unsigned long event, void *ptr)
>  {
> -	/*
> -	 * If firmware-assisted dump has been registered then trigger
> -	 * firmware-assisted dump and let firmware handle everything else.
> -	 */
> -	crash_fadump(NULL, ptr);
> -	ppc_md.panic(ptr);  /* May not return */
> +	if (is_fadump_active()) {

Should it be !fw_dump.dump_registered check ? The function crash_dump()
already checks for !fw_dump.dump_registered before proceeding. If fadump
has not been registered then the crash_dump() will return immediately
without doing anything and then fall through next line ppc_md.panic(ptr).

fadump active is always false in the first kernel (production kernel).
Hence is_fadump_active() check here would stop triggering fadump even if
it is registered.

fadump active is true only during second kernel (dump capture kernel)
that boots after fadump crash when firmware exports 'ibm,kernel-dump'
device tree node indicating dump data is available.

Thanks,
-Mahesh.

> +		/*
> +		 * If firmware-assisted dump has been registered then trigger
> +		 * firmware-assisted dump and let firmware handle everything
> +		 * else.
> +		 */
> +		crash_fadump(NULL, ptr);
> +		ppc_md.panic(ptr);  /* May not return */
> +	}
>  	return NOTIFY_DONE;
>  }
>