LoR with buf system caused by pcm

[Nate Lawson]

Looks like my mp3 playback tried to acquire UFS lockmgr lock with the pcm
lock held.  Also, got a LoR w/ Giant through a page not present trap.  Only
the backtrace() is hand-transcribed due to it not being in dmesg.  My system
appears to be working fine and there was no crash.

dmesg
-----
pcm0: <Intel 82801CA (ICH3)> port 0x18c0-0x18ff,0x1c00-0x1cff irq 11 at
device 31.5 on pci0
pcm0: <Cirrus Logic CS4299 AC97 Codec>
Acquiring lockmgr lock "ufs" with the following non-sleepablelocks held:
exclusive sleep mutex pcm0:play:0 (pcm channel) r = 0 (0xc37a8a00) locked @ /usr/src/sys/dev/sound/pcm/dsp.c:146
Sleeping on "spread" with the following non-sleepablelocks held:
exclusive sleep mutex pcm0:play:0 (pcm channel) r = 0 (0xc37a8a00) locked @ /usr/src/sys/dev/sound/pcm/dsp.c:146
lock order reversal
 1st 0xc37a8a00 pcm0:play:0 (pcm channel) @ /usr/src/sys/dev/sound/pcm/dsp.c:146
 2nd 0xc039a0c0 Giant (Giant) @ kern/kern_synch.c:311
Stack backtrace:
...witness_lock
_mtx_lock_flags()+0xb1
msleep()+0x6c4
bwait()+0x70
spec_getpages()+0x1d5
spec_vnoperate()+0x18
ffs_getpages()+0x4bc
vnode_pager_getpages()+0x77
vm_fault()+0x8f3
trap_pfault()+0xef
trap()+0x3ad
calltrap()+0x5
--- trap 0xc
generic_copyin()+0x32
sndbuf_uiomove()+0xe1
chn_write()+0x10f
dsp_write()+0x85
spec_write()+0x190
...
write()
syscall()