[systemd-devel] systemctl status not showing still running processes in inactive .mount unit cgroups (NFS specifically)

[Colin Guthrie]

Hi,

Looking into a thoroughly broken nfs-utils package here I noticed a
quirk in systemctl status and in umount behaviour.


In latest nfs-utils there is a helper binary shipped upstream called
/usr/sbin/start-statd (I'll send a separate mail talking about this
infrastructure with subject: "Running system services required for
certain filesystems")

It sets the PATH to "/sbin:/usr/sbin" then tries to run systemctl
(something that is already broken here as systemctl is in bin, not sbin)
to start "statd.service" (again this seems to be broken as the unit
appears to be called nfs-statd.service upstream... go figure).

Either way we call the service nfs-lock.service here (for legacy reasons).

If this command fails (which it does for us for two reasons) it runs
"rpc.statd --no-notify" directly. This binary then run in the context of
the .mount unit and thus in the .mount cgroup.

That seems to work OK (from a practical perspective things worked OK and
I got my mount) but are obviously sub optimal, especially when the mount
point is unmounted.

In my case, I called umount but the rpc.statd process was still running:

[root at jimmy nfs-utils]$ pscg | grep 3256
 3256 rpcuser
4:devices:/system.slice/mnt-media-scratch.mount,1:name=systemd:/system.slice/mnt-media-scratch.mount
rpc.statd --no-notify

[root at jimmy nfs-utils]$ systemctl status mnt-media-scratch.mount
● mnt-media-scratch.mount - /mnt/media/scratch
   Loaded: loaded (/etc/fstab)
   Active: inactive (dead) since Mon 2015-01-12 09:58:52 GMT; 1min 12s ago
    Where: /mnt/media/scratch
     What: marley.rasta.guthr.ie:/mnt/media/scratch
     Docs: man:fstab(5)
           man:systemd-fstab-generator(8)

Jan 07 14:55:13 jimmy mount[3216]: /usr/sbin/start-statd: line 8:
systemctl: command not found
Jan 07 14:55:14 jimmy rpc.statd[3256]: Version 1.3.0 starting
Jan 07 14:55:14 jimmy rpc.statd[3256]: Flags: TI-RPC
[root at jimmy nfs-utils]$


As you can see the mount is dead but the process is still running and
the systemctl status output does not correctly show the status of
binaries running in the cgroup. When the mount is active the process
does actually exist in this unit's context (provided systemd is used to
do the mount - if you call "mount /path" command separately, the
rpc.statd process can end up in weird cgroups - such as your user session!)

Anyway, assuming the process is in the .mount unit cgroup, should
systemd detect the umount and kill the processes accordingly, and if
not, should calling "systemctl status" on .mount units show processes
even if it's in an inactive state?

This is with 217 with a few cherry picks on top so might have been
addressed by now.


Cheers

Col

-- 

Colin Guthrie
colin(at)mageia.org
http://colin.guthr.ie/

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