freebsd stable - Feb 2013 - mount lag, umounting returns wrong "Device busy"

Hello,

while playing with new jail features, I recognized that manually
umounting doesn't work as I'd expect.
After jail has been destroyed, the following mountpoint is active:
    /dev/gpt/jailname1ROOT on /.jail.jailname1 (ufs, local, read-only)

There was var mounted to /.jail.jailname1/var but that sucessfully umounted.
'fstat' also shows no open files in /.jail.jailname1

But when I do 'umount /.jail.jailname' I get "Device busy"
returned.
Some minutes later umounting works.
But I always have to wait some time, although nothing is open and
nothing is mounted above.

Does anybody have an idea what could cause that false "Device busy"?

-Harry

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On Fri, Feb 15, 2013 at 05:43:16PM +0100, Harald Schmalzbauer
wrote:
>  Hello,
> 
> while playing with new jail features, I recognized that manually
> umounting doesn't work as I'd expect.
> After jail has been destroyed, the following mountpoint is active:
>     /dev/gpt/jailname1ROOT on /.jail.jailname1 (ufs, local, read-only)
> 
> There was var mounted to /.jail.jailname1/var but that sucessfully
umounted.
> 'fstat' also shows no open files in /.jail.jailname1
> 
> But when I do 'umount /.jail.jailname' I get "Device
busy" returned.
> Some minutes later umounting works.
> But I always have to wait some time, although nothing is open and
> nothing is mounted above.
> 
> Does anybody have an idea what could cause that false "Device
busy"?
> 
My guess is that the jail was not dead yet and it held a reference for
/.jail.jailname1's vnode.

jls -v should show the jail.

I don't know if this can happen, but my guess is that not-yet-expired
network connections hold reference to a jail preventing it from being
destroyed. So I would definitely checkout netstat output. There may be
other posibilities, but nothing obvious comes to my mind at the moment.


-- 
Mateusz Guzik <mjguzik gmail.com>