possible umount bugs (was Re: "Panic: unmount: dangling vnode")

[Kris Kennaway]

On Mon, Mar 06, 2006 at 04:34:06PM -0500, Chad Whitacre wrote:
> Kris,
> 
> > A number of problems with umount are due to be fixed in 6.1 ...
> 
> Wow, ok. Thanks for the heads-up. That's honestly a little disappointing 
> to hear. I had hoped it was a problem with my backup script.

The rule of thumb is that user code should not cause kernel panics.
But all software has bugs, of course.

> I posted a fuller description of this and another problem last week. 
> Here's the archive link:
> 
> http://lists.freebsd.org/pipermail/freebsd-questions/2006-March/114825.html
> 
> 
> The two notes I would add to that post are:
> 
>   1. The "dangling vnode" symptom did happen one other time when the box
>      first came online several months ago. The other sysadmin rebooted
>      and no further action was taken.
> 
>   2. We do not have a core dump from the latest "dangling vnode" bout,
>      due to the system apparently hanging.
> 
> 
> Is it likely that known umount problems explain the other symptom 
> ("umount: unmount of /backup failed: Device busy")?

That's completely standard and just means something still had a file
open on that filesystem.  Use fstat or lsof to find out what.

> This is actually a production box, so I can't do too much testing on it. 
> I may be able to install the patch, though, in which case I will report 
> back.

Thanks.

Kris
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