Comment 6 for bug 536994

@Kees, Can you please do the following:

1) echo 1 >/proc/sys/kernel/lock_stat
fire the unmount command.
2) less /proc/lock_stat
If you could attach the output of the previous command then we could check if there is some lock contention occurring.

You could then disable lock_stat as follows:
3) echo 0 >/proc/sys/kernel/lock_stat
4) echo 0 > /proc/lock_stat

Thanks!