lock problems with uaudio full-duplex

Hi,
I'm trying to get usb sound working in full-duplex, but still no  
success.
Once it worked (on 5.3 with patches from appropriate PRs), and then  
it began to fail.
I've tried to use that at 5.4, then at 6.0-CURRENT - that, with  
GENERIC kernel produced some interesting kernel output (on 5.3 and  
5.4 I didn't used KDB, WITNESS and INVARIANTS).

The machine is cvsupped just before build, and `uname -a` produces:
FreeBSD pager.int.connecto.tv 6.0-CURRENT FreeBSD 6.0-CURRENT #1: Tue  
Jun 14 16:43:54 MSD 2005     root_at_pager.int.connecto.tv:/usr/obj/usr/ 
src/sys/GENERIC  i386

I've got following:

Jun 14 18:56:03 pager kernel: Sleeping on "usbsyn" with the following  
non-sleepable locks held:
kernel: exclusive sleep mutex pcm0:record:0 (pcm record channel) r =  
0 (0xc2494840) locked _at_ /usr/src/sys/modules/sound/sound/../../../dev/ 
sound/pcm/dsp.c:145

Jun 14 18:56:03 pager kernel: malloc(M_WAITOK) of "512", forcing  
M_NOWAIT with the following non-sleepable locks held:
Jun 14 18:56:03 pager kernel: exclusive sleep mutex pcm0:record:0  
(pcm record channel) r = 0 (0xc2494840) locked _at_ /usr/src/sys/modules/ 
sound/sound/../../../dev/sound/pcm/dsp.c:145

Jun 14 18:56:07 pager kernel: Sleeping on "usbdly" with the following  
non-sleepable locks held:
Jun 14 18:56:07 pager kernel: exclusive sleep mutex pcm0:record:0  
(pcm record channel) r = 0 (0xc2494840) locked _at_ /usr/src/sys/modules/ 
sound/sound/../../../dev/sound/pcm/dsp.c:363

sample code to reproduce, dmesg and kernel logs are attached.

Few word about kernel logs: Start message were sent to syslog via  
logger just before program was executed. ``Now will shutdown''  
message were sent just before signaling  to program. Program had done  
some cycles before this message.