[PATCH 0/7] arch: More wchan fixes

[Peter Zijlstra]

Hi,

Respin of the rest of the get_wchan() rework [1]. Given the many problems with
STACKTRACE this series focuses on the newer ARCH_STACKWALK since that's a
smaller set of architectures to review with a better specified interface.

The idea is to piece-wise convert the rest of the architectures to
ARCH_STACKWALK, but that can be done at leasure.

PowerPC and ARM64 are a bit funny in that their __switch_to() is in C and ends
up on the stack. For now simply mark it __sched to make it work. Mark wanted to
maybe do something different, but I think this ought to get us started.