I saw this behavior (task-hang) when I tested the fsfreeze code. I was
writing a little patch to replace fsfreeze's wait queue with a killable
queue, in this way the user can do at least "kill -9", but since the
behavior was the same before your patch I didn't send it. I don't know if we
can break any previous behavior. The funny thing here is that it's like if
fsfreeze freezes itself :)
I think freezing all tasks ain't that bad, my problem is it's not possible to
start fsfreeze -u to thaw filesystem..