Hey!
Maybe something from your initrd is acting weird?
As far as I can tell, nothing from the initrd is running. It's
basically ArchLinux's mkinitcpio run on gentoo - thus, pretty standard stuff.
It might be interesting to strace PID 1 while you are doing this. And
if that doesn't help strace the other processes you run, to see if any
of them unmounts anything.
Good idea! Actually, I found out some more stuff.
1. It's not calling ls /proc, it seems as if the auto-complete
function of the running shell triggers the problem.
2. It's not restricted to auto-completing /proc, /home triggers it as
well.
3. But it's not bash's fault, tcsh triggers it, too.
4. Auto-completing one level deeper, e.g. /usr/bin, doesn't trigger
the unmount.
( note: I've two shells running: one started by the emergency shell and
one started by the small dropbear server I manually started
for debugging purpose. Everything but dropbear is watched by strace.
The problem, of course, also occurs without dropbear.)
$ strace -f -F -p 1 -p 179 -p191 -p177
Process 1 attached
Process 179 attached
Process 191 attached
Process 177 attached
[pid 177] wait4(-1, unfinished ...
[pid 191] rt_sigsuspend([] unfinished ...
[pid 179] read(16, unfinished ...
[pid 1] fstat(14, {st_mode=S_IFREG|0644, st_size=0, ...}) = 0
[pid 1] mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS,
-1, 0) = 0x7faf0bd52000
[pid 1] read(14, strace\n, 1024) = 7
[pid 1] close(14) = 0
[pid 1] munmap(0x7faf0bd52000, 4096) = 0
[pid 1] writev(3, [{31, 4}, {systemd, 7}, {[1]: , 5}, {Child 202
(strace) died (code=ex..., 55}, {\n, 1}], 5) = 72
[pid 1] open(/proc/202/cgroup, O_RDONLY|O_CLOEXEC) = 14
[pid 1] fstat(14, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0
[pid 1] mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS,
-1, 0) = 0x7faf0bd52000
[pid 1] read(14, 8:memory:/\n7:freezer:/\n6:devices..., 1024) = 101
[pid 1] close(14) = 0
[pid 1] munmap(0x7faf0bd52000, 4096) = 0
[pid 1] waitid(P_PID, 202, {si_signo=SIGCHLD, si_code=CLD_EXITED,
si_pid=202, si_status=0, si_utime=0, si_stime=0}, WEXITED, NULL) = 0
[pid 1] waitid(P_ALL, 0, {}, WNOHANG|WEXITED|WNOWAIT, NULL) = 0
[pid 1] epoll_wait(4, unfinished ...
[pid 179] ... read resumed \n, 1) = 1
[...]
( this was the only output from systemd, so I guess it's not guilty).
auto-completing /proc
[pid 179] rt_sigprocmask(SIG_BLOCK, [INT], [], 8) = 0
[pid 179] write(2, l, 1)= 1
[pid 179] rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
[pid 179] rt_sigprocmask(SIG_BLOCK, NULL, [], 8) = 0
[pid 179] read(0, s, 1) = 1
[pid 179] rt_sigprocmask(SIG_BLOCK, [INT], [], 8) = 0
[pid 179] write(2, s, 1)= 1
[pid 179] rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
[pid 179] rt_sigprocmask(SIG_BLOCK, NULL, [], 8) = 0
[pid 179] read(0, , 1) = 1
[pid 179] rt_sigprocmask(SIG_BLOCK, [INT], [], 8) = 0
[pid 179] write(2, , 1)= 1
[pid 179] rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
[pid 179] rt_sigprocmask(SIG_BLOCK, NULL, [], 8) = 0
[pid 179] read(0, /, 1) = 1
[pid 179] rt_sigprocmask(SIG_BLOCK, [INT], [], 8) = 0
[pid 179] write(2, /, 1)= 1
[pid 179] rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
[pid 179] rt_sigprocmask(SIG_BLOCK, NULL, [], 8) = 0
[pid 179] read(0, p, 1) = 1
[pid 179] rt_sigprocmask(SIG_BLOCK, [INT], [], 8) = 0
[pid 179] write(2, p, 1)= 1
[pid 179] rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
[pid 179] rt_sigprocmask(SIG_BLOCK, NULL, [], 8) = 0
[pid 179] read(0, r, 1) = 1
[pid 179] rt_sigprocmask(SIG_BLOCK, [INT], [], 8) = 0
[pid 179] write(2, r, 1)= 1
[pid 179] rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
[pid 179] rt_sigprocmask(SIG_BLOCK, NULL, [], 8) = 0
[pid 179] read(0, o, 1) = 1
[pid 179] rt_sigprocmask(SIG_BLOCK, [INT], [], 8) = 0
[pid 179] write(2, o, 1)= 1
[pid 179] rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
[pid 179] rt_sigprocmask(SIG_BLOCK, NULL, [], 8) = 0
[pid 179] read(0, \t, 1)= 1
### tab is pushed here
[pid 179] openat(AT_FDCWD, /, O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC) = 3
[pid 179] getdents(3, /* 22 entries */, 32768) = 560
[pid 179] getdents(3, /* 0 entries */, 32768) = 0
[pid 179] close(3)= 0
[pid 179] stat(/proc, {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
[pid 179] rt_sigprocmask(SIG_BLOCK, [INT], [], 8) = 0
[pid 179] write(2, c/, 2)
# after a reboot: autocomplete, that doesn't trigger
[pid 179] read(0, \t, 1)= 1
[pid 179] stat(/usr, {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
[pid 179] openat(AT_FDCWD, /usr/,
O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC) = 3
[pid 179] getdents(3, /* 16 entries */, 32768) = 464
[pid 179] getdents(3, /* 0 entries */,
