perf-urgent-2020-11-15

 - A set of commits which reduce the stack usage of various perf event
   handling functions which allocated large data structs on stack causing
   stack overflows in the worst case.

 - Use the proper mechanism for detecting soft interrupts in the recursion
   protection.

 - Make the resursion protection simpler and more robust.

 - Simplify the scheduling of event groups to make the code more robust and
   prepare for fixing the issues vs. scheduling of exclusive event groups.

 - Prevent event multiplexing and rotation for exclusive event groups

 - Correct the perf event attribute exclusive semantics to take pinned
   events, e.g. the PMU watchdog, into account

 - Make the anythread filtering conditional for Intel's generic PMU
   counters as it is not longer guaranteed to be supported on newer
   CPUs. Check the corresponding CPUID leaf to make sure.

 - Fixup a duplicate initialization in an array which was probably cause by
   the usual copy & paste - forgot to edit mishap.