Spurious backtrace during bootup on alpha

Hi all.

I've been seeing the following message when booting up my 164SX, right
after the timecounters are set:
<snip>

Stack backtrace:
db_print_backtrace() at db_print_backtrace+0x18
backtrace() at backtrace+0x2c
sched_switch() at sched_switch+0xf4
mi_switch() at mi_switch+0x1fc
cv_wait() at cv_wait+0x260
_sema_wait() at _sema_wait+0x8c
ata_queue_request() at ata_queue_request+0x2b4
ata_getparam() at ata_getparam+0xd8
ata_identify_devices() at ata_identify_devices+0x78
ata_boot_attach() at ata_boot_attach+0x58
run_interrupt_driven_config_hooks() at
run_interrupt_driven_config_hooks+0x30
mi_startup() at mi_startup+0x144
locorestart() at locorestart+0x64
--- root of call graph ---

</snip>

This is using a yesterday's tree (as pulled from the Greek cvsup
mirror -- cvsup.gr.freebsd.org).  I buildworld'ed and buildkernel'ed
on 5.2.1-RC2 and then rebooted to my brand-new -CURRENT kernel. The
kernel config (GATEKEEPER) is a GENERIC without all the extra stuff
not available or needed in my SX (e.g. eisa, usb, extra nic's and scsi
controllers, inet6, nfs, etc.).

I didn't notice the above message when I first booted the new kernel
(since the whole process was done remotely), so I went on with my
usual "buildworld revisited" procedure (as a stress test for the new
kernel), which finished just fine. I did notice, however, that system
load was around 3 throughout the buildworld, which is kinda weird
(I've never seen anything above ~1.20 when building world on -RELENG).

I attach the output of dmesg and sysctl for this kernel, plus a dmesg
of my -RC2 kernel and of a 'boot -v' of the -CURRENT kernel. More
weird stuff ahead; intuition says that the backtrace should also
appear in the dmesg of the verbose'd boot-up, right? Ummm... Nope. No
sign of a backtrace there. Any ideas? Note that a buildworld on my
oldish pca56 takes about 6-6:30 hours, so if this backtrace stuff was
something lethal, it would have fired up during this time (I guess).
Could this be another spurious ata problem (as the backtrace seems to
suggest)?

\n\n

-- 
 Nikos "Noth" Ntarmos    | < ntarmos at ceid dot upatras dot gr >
 NetCINS Lab. _at_ C.E.I.D. | [ http://{noth,p2p}.ceid.upatras.gr/ ]
 U. of Patras - Greece   | ( 38.2594N, 21.7428E ) ( 1024D / CF95160A )