Panic at USB drive plugging in

Hi all,

as personal preference I compiled kernel with drivers as module as
possible. Recently I found that plugging in USB drives causes kernel
to panic. But it does not happen when booting with GENERIC kernel
which has USB drivers compiled in.

panic screenshot:
http://goo.gl/pIIDaF

back trace:
http://goo.gl/ww4yy6

the kernel is compiled:
FreeBSD 4cbsd 10.0-CURRENT FreeBSD 10.0-CURRENT #1 r253395: Fri Jul 19
15:20:08 CST 2013     jsli_at_4cbsd:/usr/obj/usr/src/sys/Minimal  amd64

the back trace looks like devd and something had timing issues. Any ideas?


Regards,
Jia-Shiun.