LOR on head using virtualbox between intel kms and sound, with system lockup

Hi,

I've experienced a  hard lockup on head r275563, amd64.

The hardware is a laptop with an intel graphics card.

If any further info is required just ask.

I had just launched a virtualbox VM with Windows 7, the system locked up
just after the startup sound was played in the VM, X11 disappeared and
the system locked hard and a LOR data on screen.

(I already tested recompiling the virtualbox kmod and the bug shows up
with and without 3d/2d acceleration enabled in the VM)

I copied (by hand, so sorry for any typos) the LOR data:

Lock order reversal: (sleepable after non-sleepable)
 1st 0xfffff8000874da90 so_snd (so_snd) _at_
/usr/src/sys/kern/uipc_sockbuf.c:666
 2nd 0xfffff80057ff20a0 drmslk (drmslk) _at_
/usr/src/sys/modules/drm2/i915kms/../../../dev/drm2/i915/intel_display.c:2317
KDB: stack backtrace:
db_trace_self_wrapper() at db_trace_self_wrapper+0x2b/frame
0xfffffe022ed8eff0
kdb_backtrace() at kdb_backtrace+0x39/frame 0xfffffe022ed8f0a0
witness_checkorder() at witness_checkorder+x0dad/frame 0xfffffe022ed8f130
_sx_xlock() at _sx_xlock+0x71/frame 0xfffffe022ed8f170
intel_pipe_set_base() at intel_pipe_set_base+0x77/frame 0xfffffe022ed8f1d8
drm_crtc_helper_set_config() at drm_crtc_helper_set_config+0x7c0/frame
0xfffffe022ed8f290
vt_kms_postswitch() at vt_kms_postswitch+0x5c/frame 0xfffffe022ed8f2c0
vt_window_switch() at vt_window_switch+0xc3/frame 0xfffffe022ed8f300
vtterm_cngrab() at vtterm_cngrab+0x23/frame 0xfffffe022ed8f320
cngrab() at cngrab+0x35/frame 0xfffffe022ed8f340
kdb_trap() at kdb_trap+0x183/frame 0xfffffe022ed8f3e0
trap_fatal() at ytap_fatal+0x34c/frame 0xfffffe022ed8f440
trap_pfault() at trap_pfault+0x262/frame 0xfffffe022ed8f4a0
trap() at trap+0x44c/frame 0xfffffe022ed8f5f0
calltrap() at calltrap+0x8/frame 0xfffffe022ed8f5f0
--- trap 0xc, tip = 0xffffffff8056834d, rsp = 0xfffffe022ed8f6b0, rbp =
0xfffffe022ed8f6e0 ---
sbappendstream_locked() at sbappendstream_locked+0x2d/frame
0xfffffe022ed8f6e0
sbappendstream() at sbappendstream+0x3c/frame 0xfffffe022ed8f710
tcp_usr_send() at tcp_usr_send+0x1ab/frame 0xfffffe022ed8f790
sosend_generic() at sosend_generic+0x40b/frame 0xfffffe022ed8f850
kern_sendit() at kern_sendit+0x19e/frame 0xfffffe022ed8f900
sendit() at sendit+0x129/frame 0xfffffe022ed8f950
sys_sendto() at sys_sendto+0x4d/frame 0xfffffe022ed8f9a0
amd64_syscall() at amd64_syscall+0x211/frame 0xfffffe022ed8fab0
Xfast_syscall() at Xfast_syscall+0xfb/frame 0xfffffe022ed8fab0
--- syscall (133, FreeBSD ELF64, sys_sendto), rip = 0x80126c5a, rsp =
0x7fffdf1e9df8, rbp = 0x7fffdf1e9e40 ---

Please note that this is the last one, but at least another one, almost
identical to this one, was scrolled up. I've been unable to recover
their data, since, as I said the system is hard locked and did not even
write them to any system log.

Anyone can help? should this one be looked into? How can I try to debut
it more?

Thanks in advance!

-- 
Guido Falsi <mad_at_madpilot.net>