Today I ran into a situation where gluster was stuck. You could check info and status, but nothing more spectacular. When you tried enabling profiling or heal you'd get in log:
[2012-12-13 15:40:07.881363] E [glusterd-utils.c:277:glusterd_lock] 0-glusterd: Unable to get lock for uuid: c3ce6b9c-6297-4e77-924c-b44e2c13e58f, lock held by: c3ce6b9c-6297-4e77-924c-b44e2c13e58f
As can be seen the node itself can't get a lock that it itself is holding. Googling around it seems that the error comes from a command that failed to complete correctly and didn't release the lock. The web talks that this lock should auto-disappear in 30 minutes, but that's not the best solution. Also I was able to get rid of the lock a few times with
gluster volume statedump home0
but not always. When I managed to clear the lock things seemed to work (profiling started and gave info etc), but when I ran again
gluster volume heal home0
it locked up again. In the end the only help that I got from #gluster was to unmount all clients, stop all gluster processes and restart them. That indeed cleared the locks and heal command also works, but it's not really a solution I'd like to ever see again. I've written to gluster-users list and will update this entry if I get an actual way that this should have been cleared.