[mythtv] Help debugging deadlock on mythfrontend exit with release-0-21-fixes

[Andrew Dennison]

I am getting an occasional deadlock on exit of mythfrontend with
r16131, but I've been seeing this with svn head for a while (months?).
Strace shows that mythfrontend is blocked in a FUTEX_WAIT with
infinite timeout:

strace -p 5700
Process 5700 attached - interrupt to quit
futex(0xb291d5b0, FUTEX_WAIT, 0, NULL <unfinished ...>

I can attach gdb to the process but I can't find a way to generate a
backtrace as the futex syscall never returns so gdb is blocked. Is
there a way to do this, or do I just have to narrow it down from the
logs?

I _think_ this is related to the media monitor as only a few file
descriptors are still open, and two of them are
18 -> /tmp/mythtv_media
36 -> /dev/hdc (dvd drive)
(the rest are /dev/nvidia*)

Anyone got some useful tips?