Comment 3 for bug 1847590

------- Comment From <email address hidden> 2019-10-14 03:34 EDT-------
commit 932bfc5aae08f3cb20c1c9f051542f5933710151
Author: Thomas Richter <email address hidden>
Date: Fri Sep 20 11:57:43 2019 +0200

s390/cpumsf: Check for CPU Measurement sampling
s390 IBM z15 introduces a check if the CPU Mesurement Facility
sampling is temporarily unavailable. If this is the case return -EBUSY
and abort the setup of CPU Measuement facility sampling.

This patch checks for concurrent sampling which has been introduced with z15.
If machine wide sample is currently active, do not start CPU Measurement facility sampling using the perf
tool. The z15 CPU Measurement facility hardware on z15 now has a bit set when machine wide
sampling is active. This bit can be queried and when it is set the CPU Measurement facility sampling
device driver does not allow CPU specific sample and the perf_event_open() system call returns
-EBUSY in this case

Before z15 this situation could not be detected.

Applied seamlessly on all requested kernels 4.15 , 5.0 and 5.3 ...