Hi Greg, Sasha,
Please consider the attached backport of f91072ed1b72 ("perf/core: Fix race in the perf_mmap_close() function") for v4.14.y, v4.19.y and v5.4.y This will not apply in v4.9.y and v4.4.y and I am sending separate backport for that.
-- Regards Sudip