!EARLY_AP_STARTUP and -CURRENT

I'm dealing with a shit sandwich right now where the mps(4) or cam_da
reorders drives on a few thousand legacy MBR machines I have (and I
can't easily install glabel ATM), and !EARLY_AP_STARTUP seems to have
regressed.  I'd like to be able to run w/o EARLY_AP_STARTUP right
quick so I can take a more leisurely approach to fixing mps(4) boot
probe correctly (freebsd-scsi_at_ has that thread).

With WITNESS and !EARLY_AP_STARTUP I hit an assert in sched_setpreempt
in kern/sched_ule.c 100% of the time.  Here are a couple invocations,
with oddness around a different CPU holding the curthread lock but
somehow a different AP is runnable in the function:

Tracing pid 11 tid 100020 td 0xfffff80128cd1560
kdb_enter() at kdb_enter+0x3b/frame 0xfffffe3e653dcc10
vpanic() at vpanic+0x1b9/frame 0xfffffe3e653dcc90
panic() at panic+0x43/frame 0xfffffe3e653dccf0
__mtx_assert() at __mtx_assert+0xb4/frame 0xfffffe3e653dcd00
sched_add() at sched_add+0x152/frame 0xfffffe3e653dcd40
intr_event_schedule_thread() at intr_event_schedule_thread+0xca/frame
0xfffffe3e653dcd80
swi_sched() at swi_sched+0x6c/frame 0xfffffe3e653dcdc0
softclock_call_cc() at softclock_call_cc+0x155/frame 0xfffffe3e653dce70
callout_process() at callout_process+0x1f9/frame 0xfffffe3e653dcef0
handleevents() at handleevents+0x1a4/frame 0xfffffe3e653dcf30
cpu_initclocks_ap() at cpu_initclocks_ap+0xc8/frame 0xfffffe3e653dcf60
init_secondary_tail() at init_secondary_tail+0x1e3/frame 0xfffffe3e653dcf90
init_secondary() at init_secondary+0x2b3/frame 0xfffffe3e653dcff0


db> show thread 0xfffff80128cd1560
Thread 100020 at 0xfffff80128cd1560:
 proc (pid 11): 0xfffff80128cb5000
 name: idle: cpu17
 stack: 0xfffffe3e5cd88000-0xfffffe3e5cd8bfff
 flags: 0x40024  pflags: 0x200000
 state: CAN RUN
 priority: 255
 container lock: sched lock 0 (0xffffffff81c39800)
db> show lock 0xffffffff81c39800
 class: spin mutex
 name: sched lock 0
 flags: {SPIN, RECURSE}
 state: {OWNED}
 owner: 0xfffff80128cca000 (tid 100017, pid 11, "idle: cpu14")


db> bt
Tracing pid 11 tid 100021 td 0xfffff80128cd2000
kdb_enter() at kdb_enter+0x3b/frame 0xfffffe3e655e4c10
vpanic() at vpanic+0x1b9/frame 0xfffffe3e655e4c90
panic() at panic+0x43/frame 0xfffffe3e655e4cf0
__mtx_assert() at __mtx_assert+0xb4/frame 0xfffffe3e655e4d00
sched_add() at sched_add+0x152/frame 0xfffffe3e655e4d40
intr_event_schedule_thread() at intr_event_schedule_thread+0xca/frame
0xfffffe3e655e4d80
swi_sched() at swi_sched+0x6c/frame 0xfffffe3e655e4dc0
softclock_call_cc() at softclock_call_cc+0x155/frame 0xfffffe3e655e4e70
callout_process() at callout_process+0x1f9/frame 0xfffffe3e655e4ef0
handleevents() at handleevents+0x1a4/frame 0xfffffe3e655e4f30
cpu_initclocks_ap() at cpu_initclocks_ap+0xc8/frame 0xfffffe3e655e4f60
init_secondary_tail() at init_secondary_tail+0x1e3/frame 0xfffffe3e655e4f90
init_secondary() at init_secondary+0x2b3/frame 0xfffffe3e655e4ff0
db> show thread 0xfffff80128cd2000
Thread 100021 at 0xfffff80128cd2000:
 proc (pid 11): 0xfffff80128cb6000
 name: idle: cpu18
 stack: 0xfffffe3e5cf17000-0xfffffe3e5cf1afff
 flags: 0x40024  pflags: 0x200000
 state: CAN RUN
 priority: 255
 container lock: sched lock 0 (0xffffffff81c39800)
db> show lock 0xffffffff81c39800
 class: spin mutex
 name: sched lock 0
 flags: {SPIN, RECURSE}
 state: {OWNED}
 owner: 0xfffff80128cdb560 (tid 100028, pid 11, "idle: cpu25")

Regards,
Kevin