Comment # 5 on bug 1186724 from Takashi Iwai

Similar bugs have been reported in many other places since years ago, and maybe
it's not been fixed properly.  e.g.
  https://bugs.gentoo.org/775299
  https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1724232
  https://bbs.archlinux.org/viewtopic.php?id=231795

(although most of them seem hitting the crash in a slightly later code path in
hci_conn_del_sysfs()).

The duplicated sysfs entry implies that the registration has been processed
before the previous one gets unregistered, likely some race condition.