Consistent file system hang with RELENG_6 of today ...

[Robert Watson]

On Thu, 28 Jul 2005, Marc G. Fournier wrote:

> 'k, I'm starting to play with 6.x, for our new server ... my priority 
> right now is to just have it run the existing 'jail' environments from 
> my 4.x machine, while I work on getting all of our servers up to 6.x, 
> and then will worry about the jail's themselves ...
>
> When I try and startup the 4.x jail on my 6.x machine, it "hangs" the 
> file system that the jail directory hierarchy happens to be mounted on 
> though ... twice in a row so far ...
>
> Now, I'm suspecting (and am going to try without it) that it might be 
> because I'm mounting devfs within the 4.x jail, but even then, it 
> shouldn't hang things up, only generate a whack of errors ...
>
> I have a good dump (CTL-ALT-ESC -> panic), but do not have a clue what 
> to offer from within there that might be of any use ...
>
> If anyone is interested ... ?

If you can get into DDB and have serial console output, the following 
would be useful:

The output of 'show pcpu'

The output of 'show pcpu X' for each present cpu, starting with 0.

The output of 'ps'

The output of 'trace' for the currently running thread, and each non-idle 
thread shown in the show pcpu output

The output of 'show lockedvnods'

It would also be useful if, relating to the startup of the jail, you can 
identify the point in the jail boot where it wedges, and if you hit 
Ctrl-T, what process is shown as running and what state it is in, and 
using DDB, trace that process.

If you could show the trace output for each process listed in "show 
lockevnods".

Likely, there is a leaked lock or a low buffer condition.  However, once 
we have the above output we should be able to say more.  The above will 
hopefully tell us whether it's a vnode deadlock, and ideally, the 
approximate source.

Robert N M Watson