"top" sees multiple instances of:
6008 root 20 3184 D 0 0:00.06 flush_cpu sshd: root@pts/13
This is 2.6.27rc5, preemption and tickless turned on, on a 4-CPU machine.
(OK, two hyperthreaded ones :-P) strace() shows that this happens on the
last close of its /dev/ptmx file descriptor, which hangs.
I'll do a bisect early next week unless somebody else identifies a likely