panic in drm_ioctl

Hi. My box just crashed with

panic: mtx_lock() of destroyed mutex _at_ /usr/src/sys/kern/kern_mutex.c:151
KDB: stack backtrace:
db_trace_self_wrapper(c07268c7,d6131ad8,c054562a,c0724173,c079ff00,...) at db_trace_self_wrapper+0x26
kdb_backtrace(c0724173,c079ff00,c0723186,d6131ae4,d6131ae4,...) at kdb_backtrace+0x29
panic(c0723186,c072304c,97,c0571e48,c079fd50,...) at panic+0xaa
_mtx_lock_flags(c29ee8c0,0,c072304c,97,d6131b44,...) at _mtx_lock_flags+0x59
lock_mtx(c29ee8c0,0,c0724b6b,eb,0,...) at lock_mtx+0x29
_sleep(c3ef9d84,c29ee8c0,154,c07133ca,bb8,...) at _sleep+0x3bd
i915_irq_wait(c29e6300,80046445,c43885d0,3,c38b1800,...) at i915_irq_wait+0x16d
drm_ioctl(c29e6300,80046445,c43885d0,3,c38b1800,...) at drm_ioctl+0x337
giant_ioctl(c29e6300,80046445,c43885d0,3,c38b1800,...) at giant_ioctl+0x56
devfs_ioctl_f(c3004510,80046445,c43885d0,c388ad80,c38b1800,...) at devfs_ioctl_f+0xc9
kern_ioctl(c38b1800,4,80046445,c43885d0,9baad5,...) at kern_ioctl+0x243
ioctl(c38b1800,d6131cfc,c,d6131ca0,c07612b0,...) at ioctl+0x134
syscall(d6131d38) at syscall+0x288
Xint0x80_syscall() at Xint0x80_syscall+0x20
--- syscall (54, FreeBSD ELF32, ioctl), eip = 0x286d9a1f, esp = 0xbfbfe04c, ebp = 0xbfbfe068 ---

This is a ~7 days old -CURRENT with INVARIANTS and i915drm.
Is there any point investigating this? Or should I just csup and hope 
that that will fix it? :)

(I still have a debug kernel and core file if anyone is interested.)

Cheers
Michiel