[geom, cam] Hang near end of kernel probes since r213267 (likely earlier)

[David Wolfskill]

On Mon, Oct 04, 2010 at 10:44:18AM +0300, Andriy Gapon wrote:
> ...
> Interesting!

:-}

> So, init thread is blocked in vfs_mountroot()->g_waitidle() waiting for geom to
> complete probing cd device, but the latter is blocked in cam_periph_getccb()
> waiting for a ccb.
> Can you try to reproduce this again and examine other thread for anything
> interesting in geom/cam department?  Thread named as "xpt_thrd" might be of
> particular interest.

Yes; I can do that.  Bearing in mind that each of us has a finite
number of keystrokes in his (or her) life, typing all that stuff
by hand, though, tends to eat into that upper limit a bit faster than
most other forms of recreation do. :-}

Is there a way I can use USB or firewire in a way similar to a serial
console?  The laptop has both of those (though I only have connectors
for USB at the moment), and does not have a DB9 (let alone a DB25)
serial port.  I'd welcome a pointer.

Anyway: I have a couple of slices where I can re-create it:

* Slice 3 uses "standard ATA", and runs head as of r213322.

* Slice 4 uses ATA_CAM and is presently running head as of r213400.

Symptoms are fairly similar in each, though ?I seem to see the hang less
frequently when I use ATA_CAM.

In either case, PID 8 is [xpt_thrd], and wmesg is "ccb_scan".

I'll hold off on transcribing the backtrace for PID 8, in hope of being
able to let the machine do the clerical work. :-}

> We urgently need geom and cam experts here :-)

Given sufficient pointers on actions to take, patches to apply, or
code to hack, I'm willing.

Peace,
david
-- 
David H. Wolfskill				david at catwhisker.org
Depriving a girl or boy of an opportunity for education is evil.

See http://www.catwhisker.org/~david/publickey.gpg for my public key.
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