Comment # 6 on bug 1161138 from Jan Kara

So I've downloaded Leap 15.1 DVD and reproduced the issue. The problem is that
/ is actually a bind-mount of /mounts/instsys on the original tmpfs filesystem
and filesystems such as /proc were mounted in that original filesystem so they
are not children of the current filesystem mounted on / directory. Full
mountinfo is:

26 21 7:0 / /parts/mp_0000 ro,relatime - squashfs /dev/loop0 ro
27 21 7:1 / /parts/mp_0001 ro,relatime - squashfs /dev/loop1 ro
23 21 0:6 / /dev rw,relatime - devtmpfs devtmpfs
rw,size=1904852k,nr_inodes=476213,mode=755
32 21 7:2 / /mounts/mp_0000 ro,relatime - squashfs /dev/loop2 ro
33 21 7:3 / /mounts/mp_0001 ro,relatime - squashfs /dev/loop3 ro
34 21 7:4 / /mounts/mp_0002 ro,relatime - squashfs /dev/loop4 ro
35 21 0:20 /mounts/instsys / rw,relatime - tmpfs tmpfs
rw,size=3916000k,nr_inodes=0
28 21 0:21 / /sys rw,relatime - sysfs sysfs rw
36 21 0:5 / /proc rw,relatime - proc proc rw
37 28 0:7 / /sys/kernel/security rw,nosuid,nodev,noexec,relatime - securityfs
securityfs rw
38 23 0:22 / /dev/shm rw,nosuid,nodev - tmpfs tmpfs rw
39 23 0:26 / /dev/pts rw,relatime - devpts devpts
rw,gid=5,mode=620,ptmxmode=000
40 21 0:27 / /run rw,nosuid,nodev - tmpfs tmpfs rw,mode=755
41 28 0:28 / /sys/fs/cgroup ro,nosuid,nodev,noexec - tmpfs tmpfs ro,mode=755
42 41 0:29 / /sys/fs/cgroup/unified rw,nosuid,nodev,noexec,relatime - cgroup2
cgroup rw
43 41 0:30 / /sys/fs/cgroup/systemd rw,nosuid,nodev,noexec,relatime - cgroup
cgroup rw,xattr,name=systemd
44 28 0:31 / /sys/fs/pstore rw,nosuid,nodev,noexec,relatime - pstore pstore rw
45 28 0:24 / /sys/firmware/efi/efivars rw,nosuid,nodev,noexec,relatime -
efivarfs efivarfs rw
46 41 0:32 / /sys/fs/cgroup/pids rw,nosuid,nodev,noexec,relatime - cgroup
cgroup rw,pids
47 41 0:33 / /sys/fs/cgroup/cpuset rw,nosuid,nodev,noexec,relatime - cgroup
cgroup rw,cpuset
48 41 0:34 / /sys/fs/cgroup/freezer rw,nosuid,nodev,noexec,relatime - cgroup
cgroup rw,freezer
49 41 0:35 / /sys/fs/cgroup/cpu,cpuacct rw,nosuid,nodev,noexec,relatime -
cgroup cgroup rw,cpu,cpuacct
50 41 0:36 / /sys/fs/cgroup/net_cls,net_prio rw,nosuid,nodev,noexec,relatime -
cgroup cgroup rw,net_cls,net_prio
51 41 0:37 / /sys/fs/cgroup/memory rw,nosuid,nodev,noexec,relatime - cgroup
cgroup rw,memory
52 41 0:38 / /sys/fs/cgroup/perf_event rw,nosuid,nodev,noexec,relatime - cgroup
cgroup rw,perf_event
53 41 0:39 / /sys/fs/cgroup/rdma rw,nosuid,nodev,noexec,relatime - cgroup
cgroup rw,rdma
54 41 0:40 / /sys/fs/cgroup/hugetlb rw,nosuid,nodev,noexec,relatime - cgroup
cgroup rw,hugetlb
55 41 0:41 / /sys/fs/cgroup/devices rw,nosuid,nodev,noexec,relatime - cgroup
cgroup rw,devices
56 41 0:42 / /sys/fs/cgroup/blkio rw,nosuid,nodev,noexec,relatime - cgroup
cgroup rw,blkio
57 36 0:43 / /proc/sys/fs/binfmt_misc rw,relatime - autofs systemd-1
rw,fd=37,pgrp=1,timeout=0,minproto=5,maxproto=5,direct,pipe_ino=34865
58 28 0:8 / /sys/kernel/debug rw,relatime - debugfs debugfs rw
59 23 0:19 / /dev/mqueue rw,relatime - mqueue mqueue rw
60 23 0:44 / /dev/hugepages rw,relatime - hugetlbfs hugetlbfs rw
61 21 0:27 / /var/run rw,nosuid,nodev - tmpfs tmpfs rw,mode=755
62 40 0:45 / /run/user/0 rw,nosuid,nodev,relatime - tmpfs tmpfs
rw,size=391600k,mode=700
63 21 8:49 / /mnt rw,relatime - vfat /dev/sdd1
rw,fmask=0022,dmask=0022,codepage=437,iocharset=iso8859-1,shortname=mixed,errors=remount-ro

Notice how all substantial mounts are children (the second column) of mount 21,
which is not visible in mountinfo because it is no longer reachable from
current mount tree.

This leads to the weird and confusing result that if you try resolving any
relative pathname, the resolution will happen relative to mount 35 (bind
mounted to /) which has no children so you just will not see any of other
filesystems as mounted. If you resolve an absolute path (starting with /), the
resolution will start relative to mount 21 and thus you will see all
filesystems as mounted.

So the mount hierarchy looks to be setup in a weird way. I'm not sure how that
is exactly handled for the rescue system. Yast2 guys? How is the mount
hierarchy created in the rescue system?