Description: perf: Fix race in perf_mmap_close function
References:
 https://lore.kernel.org/lkml/20200910104153.1672460-1-jolsa@kernel.org/
Notes:
 carnil> Commit fixes 9bb5d40cd93c ("perf: Fix mmap() accounting hole")
 carnil> in 3.10-rc7.
 carnil> For v5.9.y fixed in 5.9.2
Bugs:
upstream: released (5.10-rc1) [f91072ed1b7283b13ca57fcfbece5a3b92726143]
4.19-upstream-stable: released (4.19.158) [1cbfb60332f4e62224440f6d38a6b3114b2355f0]
4.9-upstream-stable: released (4.9.244) [5a097d643717160d859f5bd4a29e2088f48a5fd3]
sid: released (5.9.6-1)
4.19-buster-security: released (4.19.160-1)
4.9-stretch-security: released (4.9.246-1)