semi-OT: how to backtrace into the kernel when it's stuck

[David Zeuthen]

On Wed, 2005-12-14 at 16:04 +0100, dannym wrote:
> Hi,
> 
> this is kind of off-topic but ...
> 
> You know, I have this dvd drive...
> 
> when hald is running and I issue mount on the drive, mount will hang and
> not let itself be killed by any means. (the mount will neither succeed
> nor fail but will just be "halted")

Yes, both mount and one or more hald-addon-storage processes is in state
D (uninteruptible IO), right?

(use ps aux to find the state)

> 
> when hald is not running, it works fine.
> 
> Now I thought it would be nice if I could debug that and for that it
> would be nice to see where in the kernel it is waiting around (for some
> lock, I suppose) for that mount process.
> 
> Any ideas how to debug this on the hal side would be nice too :)

Well, a helper of hald is simply polling the drive so we can detect
media changes and I believe the driver in the kernel gets very confused
and somehow stops servicing IO from user-space processes. 

The kernel shouldn't do this, I submit this is a bug with the kernel. To
answer your question, no, I don't really know how to fix this, sorry.

Cheers,
David