non-sleepable locks held

I got following messages on console:


malloc() of "256" with the following non-sleepable locks held:
exclusive sleep mutex pcm0 (sound cdev) r = 0 (0xc3800600) locked _at_ 
/usr/home/davidxu/src/sys/dev/sound/pcm/dsp.c:213
lock order reversal
  1st 0xc3b85a38 filedesc structure (filedesc structure) _at_ 
kern/sys_generic.c:901
  2nd 0xc0927ca0 Giant (Giant) _at_ fs/specfs/spec_vnops.c:377
Stack backtrace:
backtrace(c086e5e9,c0927ca0,c086a64a,c086a64a,c0865c89) at backtrace+0x17
witness_checkorder(c0927ca0,9,c0865c89,179,1) at witness_checkorder+0x6f8
_mtx_lock_flags(c0927ca0,0,c0865c80,179,c086ec03) at _mtx_lock_flags+0x9d
spec_poll(d7658afc,d7658b1c,c06aad6c,d7658afc,c0909e20) at spec_poll+0x134
spec_vnoperate(d7658afc,c0909e20,c390a30c,40,c3c37b00) at 
spec_vnoperate+0x18
vn_poll(c3ebbd8c,40,c4010180,c383b540,c4010180) at vn_poll+0x3c
selscan(c383b540,d7658b9c,d7658b8c,9,4) at selscan+0x141
kern_select(c383b540,9,80692b0,80692c0,0) at kern_select+0x37f
select(c383b540,d7658d14,14,438,5) at select+0x66
syscall(2f,2f,2f,3,0) at syscall+0x2a0
Xint0x80_syscall() at Xint0x80_syscall+0x1d
--- syscall (93), eip = 0x282a28ab, esp = 0xbfbfe6cc, ebp = 0xbfbfe778 ---
malloc() of "256" with the following non-sleepable locks held:
exclusive sleep mutex pcm0 (sound cdev) r = 0 (0xc3800600) locked _at_ 
/usr/home/davidxu/src/sys/dev/sound/pcm/dsp.c:213
malloc() of "256" with the following non-sleepable locks held:
exclusive sleep mutex pcm0 (sound cdev) r = 0 (0xc3800600) locked _at_ 
/usr/home/davidxu/src/sys/dev/sound/pcm/dsp.c:213