Hello Kir, James B, and whoever has insteresed in aufs proc_mounts.patch, In linux-v5.8-rc1, a commit was merged, 9f6c61f96f2d9 2020-05-14 proc/mounts: add cursor whose purpose is same to aufs proc_mounts.patch.
I didn't test v5.8 so deeply yet, but the commit looks working and aufs proc_mounts.patch is not necessary anymore. I am going to remove proc_mounts.patch from aufs release, and revert a few commits in aufs-util.git whose major parts were developed by Kir. If you can, could you confirm the behaviour of /proc/mounts in v5.8 and post the result here? J. R. Okajima