/proc/diskstats reports incorrect disk read stats in 5.11.0-46 HWE kernel in Ubuntu 20.04. 5.4.0-94 kernel is OK

Hd-idle stopped working when I installed the 5.11 HWE kernel on Ubuntu 20.04. I eventually found that /proc/diskstats was reporting phantom disk read activity. Here are the stats for one of my drives running under 5.4.0. I've underlined the disk read counter that's used by hd-idle to check disk activity:

grep sdg /proc/diskstats 
   8      96 sdg 12758 4 793104 49835 446 0 7840 262 0 47720 39172 0 0 0 0
                         ------
   8      97 sdg1 12606 4 787936 49248 446 0 7840 262 0 47308 38712 0 0 0 0
   8     105 sdg9 41 0 576 94 0 0 0 0 0 112 68 0 0 0 0

The HWE kernel (5.11) reports continuously increasing disk reads on the raw device at maybe 5 to 10 reads per second and this prevents hd-idle from spinning down the drive. Note that there's no read activity on the individual partitions.

The disk itself appears to be really idle because I can force it to spin-down (using 'hd-idle -t sdg') and it doesn't immediately spin back up.

So, it appears the 5.11 HWE kernel is reporting phantom read I/O that isn't really there. As I said in the title, the 5.4 kernel works correctly.

This drive is one of six hard drives that are members of a ZFS zpool and all of them have this issue. My other, system, drives are an NVME SSD and a 2.5" SSD and I don't know if they also report phantom disk reads because they never go completely idle.

FWIW, I searched launchpad and bugzilla.kernel.org and I don't see any bugs or reports that match this behavior.

Update 01/17/22: Same problem occurs on Linux 5.8.0-63. Here's another demonstration (on 5.8.0) of the issue where diskstats shows reads occurring to a drive that's actually spun down and sleeping:

$ sudo hd-idle -t sdg
$ hddtemp /dev/sdg
/dev/sdg: HGST HDN726040ALE614: drive is sleeping
$ grep sdg /proc/diskstats
   8      96 sdg 6272 2 48966 34365 345 1 5952 315 0 21544 34858 0 0 0 0 12 177
   8      97 sdg1 3279 2 42088 29129 345 1 5952 315 0 16584 29445 0 0 0 0 0 0
   8     105 sdg9 41 0 576 86 0 0 0 0 0 104 86 0 0 0 0 0 0
$ sleep 5
$ grep sdg /proc/diskstats
   8      96 sdg 6302 2 48986 34367 345 1 5952 315 0 21580 34860 0 0 0 0 12 177
   8      97 sdg1 3279 2 42088 29129 345 1 5952 315 0 16584 29445 0 0 0 0 0 0
   8     105 sdg9 41 0 576 86 0 0 0 0 0 104 86 0 0 0 0 0 0
$ hddtemp /dev/sdg
/dev/sdg: HGST HDN726040ALE614: drive is sleeping