panic on 5.2 BETA: blockable sleep lock

I got the following panic twice when starting xawtv using 5.2 BETA (CVS
from Oct 23)
panic: blockable sleep lock (sleep mutex) sellck
_at_/usr/src/sys/kern/sys_generic.c:1145

I don't think it is directly related to bktr since the last commit there
was ~3 months ago. Here is the dmesg output for completeness though.
bktr0: <BrookTree 878> mem 0xdf103000-0xdf103fff irq 10 at device 12.0
on pci0
bktr0: Card has no configuration EEPROM. Cannot determine card make.
bktr0: IMS TV Turbo, Philips FR1236 NTSC FM tuner.


Here is a backtrace:

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panic: blockable sleep lock (sleep mutex) sellck _at_
/usr/src/sys/kern/sys_generic.c:1145
panic messages:
--
panic: blockable sleep lock (sleep mutex) sellck _at_
/usr/src/sys/kern/sys_generic.c:1145

syncing disks, buffers remaining... 3023 3023 panic: mi_switch: switch
in a critical section
Uptime: 6m28s
Dumping 383 MB
16 32 48 64 80[CTRL-C to abort] [CTRL-C to abort] [CTRL-C to abort]  96
112 128 144 160 176 192 208 224 240[CTRL-C to abort] [CTRL-C to abort]
[CTRL-C to abort]  256 272 288 304 320 336 352 368
--
Reading symbols from /boot/kernel/snd_pcm.ko...done.
Loaded symbols for /boot/kernel/snd_pcm.ko
Reading symbols from /boot/kernel/snd_csa.ko...done.
Loaded symbols for /boot/kernel/snd_csa.ko
Reading symbols from /boot/kernel/bktr.ko...done.
Loaded symbols for /boot/kernel/bktr.ko
Reading symbols from /boot/kernel/bktr_mem.ko...done.
Loaded symbols for /boot/kernel/bktr_mem.ko
Reading symbols from
/usr/obj/usr/src/sys/SHOE/modules/usr/src/sys/modules/linprocfs/linprocfs.ko.debug...done.
Loaded symbols for
/usr/obj/usr/src/sys/SHOE/modules/usr/src/sys/modules/linprocfs/linprocfs.ko.debug
Reading symbols from
/usr/obj/usr/src/sys/SHOE/modules/usr/src/sys/modules/linux/linux.ko.debug...done.
Loaded symbols for
/usr/obj/usr/src/sys/SHOE/modules/usr/src/sys/modules/linux/linux.ko.debug
Reading symbols from
/usr/obj/usr/src/sys/SHOE/modules/usr/src/sys/modules/ext2fs/ext2fs.ko.debug...done.
Loaded symbols for
/usr/obj/usr/src/sys/SHOE/modules/usr/src/sys/modules/ext2fs/ext2fs.ko.debug
Reading symbols from
/usr/obj/usr/src/sys/SHOE/modules/usr/src/sys/modules/ntfs/ntfs.ko.debug...done.
Loaded symbols for
/usr/obj/usr/src/sys/SHOE/modules/usr/src/sys/modules/ntfs/ntfs.ko.debug
Reading symbols from
/usr/obj/usr/src/sys/SHOE/modules/usr/src/sys/modules/if_tap/if_tap.ko.debug...done.
Loaded symbols for
/usr/obj/usr/src/sys/SHOE/modules/usr/src/sys/modules/if_tap/if_tap.ko.debug
Reading symbols from /boot/kernel/netgraph.ko...done.
Loaded symbols for /boot/kernel/netgraph.ko
Reading symbols from /boot/kernel/ng_ether.ko...done.
Loaded symbols for /boot/kernel/ng_ether.ko
Reading symbols from /boot/kernel/ng_bridge.ko...done.
Loaded symbols for /boot/kernel/ng_bridge.ko
Reading symbols from /boot/kernel/ng_socket.ko...done.
Loaded symbols for /boot/kernel/ng_socket.ko
#0  doadump () at /usr/src/sys/kern/kern_shutdown.c:240
240 dumping++;
(kgdb) bt
#0  doadump () at /usr/src/sys/kern/kern_shutdown.c:240
#1  0xc051502c in boot (howto=260) at
/usr/src/sys/kern/kern_shutdown.c:372
#2  0xc05153b7 in panic () at /usr/src/sys/kern/kern_shutdown.c:550
#3  0xc051d0c5 in mi_switch () at /usr/src/sys/kern/kern_synch.c:470
#4  0xc0514d18 in boot (howto=256) at
/usr/src/sys/kern/kern_shutdown.c:312
#5  0xc05153b7 in panic () at /usr/src/sys/kern/kern_shutdown.c:550
#6  0xc053c010 in witness_lock (lock=0xc076cf40, flags=8, 
    file=0xc06d2139 "/usr/src/sys/kern/sys_generic.c", line=1145)
    at /usr/src/sys/kern/subr_witness.c:609
#7  0xc050b57a in _mtx_lock_flags (m=0xc3a56dc0, opts=0, 
    file=0xc06ff79c "\037#nÀ\t", line=-1065955520)
    at /usr/src/sys/kern/kern_mutex.c:221
#8  0xc0540436 in selrecord (selector=0xc076cf40, sip=0xc3a56dc0)
    at /usr/src/sys/kern/sys_generic.c:1145
#9  0xc08509f1 in bktr_poll () from /boot/kernel/bktr.ko
#10 0xc04cbb00 in spec_poll (ap=0xd38ceafc)
    at /usr/src/sys/fs/specfs/spec_vnops.c:379
#11 0xc04caf38 in spec_vnoperate (ap=0x0)
    at /usr/src/sys/fs/specfs/spec_vnops.c:122
#12 0xc057ca1c in vn_poll (fp=0x0, events=0, active_cred=0xc3c85380,
td=0x0)
    at vnode_if.h:537
#13 0xc053fc71 in selscan (td=0xc3a56dc0, ibits=0xd38ceb9c,
obits=0xd38ceb8c, 
    nfd=6) at /usr/src/sys/sys/file.h:272
#14 0xc053f7df in kern_select (td=0xc3a56dc0, nd=6, fd_in=0xbfbfebc0, 
    fd_ou=0x0, fd_ex=0x0, tvp=0x0) at
/usr/src/sys/kern/sys_generic.c:816
#15 0xc053f446 in select (td=0x0, uap=0xd38ced14)
    at /usr/src/sys/kern/sys_generic.c:720
#16 0xc068c700 in syscall (frame=
      {tf_fs = 47, tf_es = 47, tf_ds = 47, tf_edi = -1, tf_esi =
134598312, tf_ebp = -1077941160, tf_isp = -745738892, tf_ebx = 0, tf_edx
= 6, tf_ecx = -1077941312, tf_eax = 93, tf_trapno = 0, tf_err = 2,
tf_eip = 673044815, tf_cs = 31, tf_eflags = 662, tf_esp = -1077941396,
tf_ss = 47})
    at /usr/src/sys/i386/i386/trap.c:1010
#17 0xc067d64d in Xint0x80_syscall () at {standard input}:136
(kgdb)