boot-time crash in today's -current, and other threading problems

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I'm spamming everyone who's had fingers in the threading code lately
since I can't seem to find a specific commit that looks guilty.

On 19 Nov. I updated my -current system and noticed a regression where
alpine (a new version of the pine mail client that uses threads) would
crash while opening my mail folders with a sig 6. I figured I'd wait a
day or two since it was obvious that there was some work going on with
threads, and other things were working.

Today I upgraded again, and the new kernel crashes on startup.
Traceback is below. Suggestions welcome.

Doug

...
bge0: <Broadcom NetXtreme Gigabit Ethernet Controller, ASIC rev.
0x6002> mem 0xecef0000-0xecefffff irq 18 at device 0.0 on pci9
miibus0: <MII bus> on bge0
brgphy0: <BCM5752 10/100/1000baseTX PHY> PHY 1 on miibus0
brgphy0:  10baseT, 10baseT-FDX, 100baseTX, 100baseTX-FDX, 1000baseT,
1000baseT-FDX, auto
bge0: Ethernet address: 00:15:c5:55:f0:5b
bge0: [ITHREAD]


Fatal trap 12: page fault while in kernel mode
cpuid = 0; apic id = 00
fault virtual address   = 0xdeadc0ee
fault code              = supervisor read, page not present
instruction pointer     = 0x20:0xc0556053
stack pointer           = 0x28:0xe5b00c54
frame pointer           = 0x28:0xe5b00c64
code segment            = base 0x0, limit 0xfffff, type 0x1b
                        = DPL 0, pres 1, def32 1, gran 1
processor eflags        = interrupt enabled, resume, IOPL = 0
current process         = 11 (swi4: clock sio)
Physical memory: 2029 MB
Dumping 70 MB: 55 39 23 7

#0  doadump () at pcpu.h:195
195     pcpu.h: No such file or directory.
        in pcpu.h

(kgdb) where
#0  doadump () at pcpu.h:195
#1  0xc0455619 in db_fncall (dummy1=-441447812, dummy2=0, dummy3=582,
    dummy4=0xe5b009e8 "ÀxEÀ") at /usr/local/src/sys/ddb/db_command.c:486
#2  0xc0455b85 in db_command_loop () at
/usr/local/src/sys/ddb/db_command.c:401
#3  0xc04572f5 in db_trap (type=12, code=0)
    at /usr/local/src/sys/ddb/db_main.c:222
#4  0xc058b136 in kdb_trap (type=12, code=0, tf=0xe5b00c14)
    at /usr/local/src/sys/kern/subr_kdb.c:502
#5  0xc071f4af in trap_fatal (frame=0xe5b00c14, eva=3735929070)
    at /usr/local/src/sys/i386/i386/trap.c:863
#6  0xc071f6d0 in trap_pfault (frame=0xe5b00c14, usermode=0,
eva=3735929070)
    at /usr/local/src/sys/i386/i386/trap.c:785
#7  0xc071ff92 in trap (frame=0xe5b00c14)
    at /usr/local/src/sys/i386/i386/trap.c:463
#8  0xc0706dab in calltrap () at
/usr/local/src/sys/i386/i386/exception.s:139
#9  0xc0556053 in _mtx_assert (m=0xdeadc0de, what=20,
    file=0xc0763525 "/usr/local/src/sys/kern/kern_mutex.c", line=167)
    at /usr/local/src/sys/kern/kern_mutex.c:632
#10 0xc055676a in unlock_mtx (lock=0xdeadc0de)
    at /usr/local/src/sys/kern/kern_mutex.c:167
#11 0xc0574c3f in softclock (dummy=0x0)
    at /usr/local/src/sys/kern/kern_timeout.c:297
#12 0xc0546405 in ithread_loop (arg=0xc54daa00)
    at /usr/local/src/sys/kern/kern_intr.c:1034
#13 0xc0543988 in fork_exit (callout=0xc0546250 <ithread_loop>,
    arg=0xc54daa00, frame=0xe5b00d38)
    at /usr/local/src/sys/kern/kern_fork.c:788
#14 0xc0706e20 in fork_trampoline ()
    at /usr/local/src/sys/i386/i386/exception.s:205

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