[linux-lvm] Debugging help.

[Joe Thornber]

On Wed, Jan 24, 2001 at 09:58:23AM -0800, Jay Weber wrote:
> Hi,
> 
> I'm focusing on trying to figure out why I get system hangs in LVM
> when a snapshot is in use (or maybe it only triggers when it runs out of
> space) while there is heavy IO (although I don't think 8 consecutive cp's
> constitue heavy IO).
> 
> Any suggestions on what to turn on debugging wise?  I'm currently
> utilizing SysRq and kdb v1.5 on stock 2.2.18 with LVM patches applied from
> 0.9.1beta2 using the PATCHES/README instructions.  All I manage to get
> after the system hangs, using SysRq's PrintPC or dropping into kdb
> (manually) and doing a backtrace, is reference to cpu_idle and
> init_task_union.  This leads me to believe the system is just sitting in
> an indefinate idle loop state?
> 
> I've also initially tried enabling the debug code in lvm-snap.c but it's
> not much help since the box hangs and the info that may be output from it
> is stuck in buffer and SysRq Sync don't manage to drop it to disk for me
> after hanging.
> 
> Any clues, suggestions, hints, pointers?

I use user mode linux, if I get a hang I just hit control-C and look
what the kernels doing in gdb.

- Joe