panic: lock "aiomtx" already initialized

From stress2's random syscall test:

db> wh
Tracing pid 45777 tid 100465 td 0xc61b7000
kdb_enter(c077f50d,2,c0782352,ed0fab84,2,...) at kdb_enter+0x33
panic(c0782352,c0788b88,c5e1107c,20000,0,...) at panic+0xed
lock_init(c5e1107c,c07c67c4,c0788b88,0,20000) at lock_init+0x8c
mtx_init(c5e1107c,c0788b88,0,0,79400d31,...) at mtx_init+0x9f
aio_init_aioinfo(c61c4ab0,c057d463,c07e6520,9579c960,31a964,...) at aio_init_aioinfo+0x4b
aio_aqueue(c61b7000,79400d31,0,2,1,...) at aio_aqueue+0x8d
oaio_read(c61b7000,ed0facf8,4,c078503a,c07c2250,...) at oaio_read+0x32
syscall(ed0fad38) at syscall+0x14f
Xint0x80_syscall() at Xint0x80_syscall+0x20
--- syscall (318, FreeBSD ELF32, oaio_read), eip = 0x280c0969, esp = 0xbfbfe5f0, ebp = 0xbfbfe638 ---
db> x/s 0xc0782352
0xc0782352:     lock "%s" %p already initialized
db> x/s 0xc0788b88
0xc0788b88:     aiomtx
db> show lock 0xc5e1107c
 class: sleep mutex
 name: aiomtx
 flags: {DEF}
 state: {UNOWNED}