Trying to write a small program to record audio from radio (if I just had
some radio hardware :-), I discovered a repeatable panic.  This occurs
with Feb 9 kernel sources on two machines (one with ym audio, the other
with eap) when trying to record audio with recbuf size of 256 kbytes:

panic: kernel diagnostic assertion "umap->refcount != 0" failed:
file "/usr/src/src/sys/arch/i386/compile/LINTU/../../../../uvm/uvm_bio.c",
line 253

Stopped in pid 11631 (rec) at cpu_Debugger+0x4: leave
db> trace
cpu_Debugger(22000,c52f5000,0,c5c6ca94,20000) at cpu_Debugger+0x4
panic(c039d000,c034590d,c0345a44,c0345a60,fd) at panic+0xad
__assert(c034590d,c0345a60,fd,c0345a44,c5adbae4) at __assert+0x1f
ubc_fault(c5c6cc14,c52f5000,c5c6cb94,1,0,0,1,2) at ubc_fault+0xa5
uvm_fault(c03b4960,c52f5000,0,1,0) at uvm_fault+0x60f
trap() at trap+0x4e3
--- trap (number 6) ---
i486_copyout(c52f5800,20000,c5c6cee0,c01827d8,c0573800) at i486_copyout+0x3c
audio_read(c0573800,c5c6cee0,0,c0180422,c5c6ce3c) at audio_read+0x325
audioread(2a80,c5c6cee0,0,c0189da3,c5c4ce94) at audioread+0x7f
spec_read...
ufsspec_reac...
VOP_READ...
vn_read...
dofileread...
sys_read...
syscall_plain...

(Ten-finger copy, may contain typos)

I can do more testing if required..

  -jm