powerpc/64s: watchdog fix stack setup

[Michael Ellerman]

On Sat, 2017-07-29 at 12:50:27 UTC, Nicholas Piggin wrote:
> The watchdog soft-NMI exception stack setup loads a stack pointer
> twice, which is an obvious error. It ends up using the system reset
> interrupt (true-NMI) stack, which is also a bug because the watchdog
> could be preempted by a system reset interrupt that overwrites the
> NMI stack.
> 
> Change the soft-NMI to use the "emergency stack". The current kernel
> stack is not used, because of the longer-term goal to prevent
> asynchronous stack access using soft-disable.
> 
> Signed-off-by: Nicholas Piggin <npiggin at gmail.com>

Applied to powerpc fixes, thanks.

https://git.kernel.org/powerpc/c/cc491f1d3583146eaee635c86b9c92

cheers