Weird PostgreSQL crashes on FC2/FC3 64-bit

Since I've upgraded my development server to FC2/FC3 64-bit, I
occasionally get these weird PostgreSQL semi-lockups. Once in a while, a
query (usually a big update of some type) will just stop dead. Doing a
ps -ef | grep postgres, I will see something like:

root     17034     1  0 21:41 ?        00:00:00 gdb -q -x /dev/stdin
postgres 9131
postgres  9131  2712  0 20:31 ?        00:00:00 postgres: postgres
netdata [local] VACUUM

Other connections continue to run (unless the dead process causes a
pileup behind it) and I can make new connections to the DB.

The strange thing is I cannot kill the dead process. I can type "kill -9
9131" all day long (yes I know it's bad) but the process will not go
away. Doing kill -9 on all the other postmasters will make them go away
but the bad one will still stay forever. The gdb process is killable though.

At this point, this dead process is still on my machine. Are there any
commands for me to figure out what's going on here?