NFS + nullfs + jail = zombies?

[Ernie Luzar]

Thomas Johnson wrote:
> I am working on developing a clustered application utilizing jails and
> running into problems that seem to be NFS-related. I'm hoping that
> someone can point out my error.
> 
> The jail images and my application data are served via NFS. The host
> mounts NFS at boot, and then uses nullfs mounts to assemble the jail
> tree when the jail is created (fstab files and jail.conf are below).
> This seems to work fine, the jail starts and is usable. The problem
> comes when I remove/restart the jail. Frequently (but not
> consistently), the jail gets stuck in a dying state, causing the
> unmount of the jail root (nullfs) to fail with a "device busy" error.
> 
> # jail -f /var/local/jail.conf -r wds1-1a
> Stopping cron.
> Waiting for PIDS: 1361.
> .
> Terminated
> wds1-1a: removed
> umount: unmount of /var/jail/wds1-1a failed: Device busy
> # jls -av
>    JID  Hostname                      Path
>         Name                          State
>         CPUSetID
>         IP Address(es)
>      1  wds1-1a                       /var/jail/wds1-1a
>         wds1-1a                       DYING
>         2
>         2620:1:1:1:1a::1
> 
> Through trial-and-error I have determined that forcing an unmount of
> the root works, but subsequent mounts to that mount point will fail to
> unmount with the same error. Deleting and recreating the mountpoint
> fixes the mounting issue, but the dying jail remains permanently.
> 
> I have also found that if I copy the jail root to local storage and
> update the jail's fstab to nullfs mount this, the problem seems to go
> away. This leads me to believe that the issue is related to the NFS
> source for the nullfs mount. statd and lockd are both running on the
> host.
> 
> My relevant configurations are below. I can provide any other
> information desired.
> 
> # Host fstab line for jail root.
> #
> 10.219.212.1:/vol/dev/wds/jail_base  /jail/base nfs ro    0    0
> 
> 
> # Jail fstab file (mount.fstab)
> #
> /jail/base /var/jail/wds1-1a nullfs ro 0 0
> # writable (UFS-backed) /var
> /var/jail-vars/wds1-1a /var/jail/wds1-1a/var nullfs rw 0 0
> 
> 
> # jail.conf file
> #
> * {
>     devfs_ruleset = "4";
>     mount.devfs;
>     exec.start = "/bin/sh /etc/rc";
>     exec.stop = "/bin/sh /etc/rc.shutdown";
>     interface = "vmx1";
>     allow.dying = 1;
>     exec.prestart = "/usr/local/bin/rsync -avC --delete
> /jail/${image}/var/ /var/jail-vars/${host.hostname}/";
>     }
> 
> # JMANAGE wds1-1a
> wds1-1a {
>     path = "/var/jail/wds1-1a";
>     ip6.addr = "2620:1:1:1:1a::1";
>     host.hostname = "wds1-1a";
>     host.domainname = "dev";
>     mount.fstab = "/var/local/fstab.wds1-1a";
>     $image = "base";
> }


If I remember correctly from past posts about NFS and jails, NFS does 
not play well with jails. The jails directory tree has to be on the host 
running the jail. Remove NFS from the picture and it should just work. 
Your beating a dead horse.