[RFC, 1/4] powerpc/64: Save stack pointer when we hard disable interrupts

[Michael Ellerman]

On Wed, 2018-05-02 at 13:07:26 UTC, Michael Ellerman wrote:
> A CPU that gets stuck with interrupts hard disable can be difficult to
> debug, as on some platforms we have no way to interrupt the CPU to
> find out what it's doing.
> 
> A stop-gap is to have the CPU save it's stack pointer (r1) in its paca
> when it hard disables interrupts. That way if we can't interrupt it,
> we can at least trace the stack based on where it last disabled
> interrupts.
> 
> In some cases that will be total junk, but the stack trace code should
> handle that. In the simple case of a CPU that disable interrupts and
> then gets stuck in a loop, the stack trace should be informative.
> 
> We could clear the saved stack pointer when we enable interrupts, but
> that loses information which could be useful if we have nothing else
> to go on.
> 
> Signed-off-by: Michael Ellerman <mpe at ellerman.id.au>

Series applied to powerpc next.

https://git.kernel.org/powerpc/c/7b08729cb272b4cd5c657cd5ac0ddd

cheers