gah ... okay, first "problem" is coming up with a serial console, as I
only have the one machine ... but, am going to search one out and save
this email ... will come back to it once I get it setup that far ...

thanks ...

On Tue, 28 Nov 2000, John Baldwin wrote:

> On 28-Nov-00 The Hermit Hacker wrote:
> > 
> > Just tried to build a kernel based on sources from today, to enable
> > BREAK_TO_DEBUGGER so that I can try and get in and see where its hanging
> > ... the compile hung the machine solid.  Even hitting the
> > 'numlock'/'capslock' on my keyboard generated no results ...
> It is spinning with interrupts disabled, probably due to holding a spinlock for
> far too long.  Debugging this is not all that fun.  :-P  If you can rig up an
> NMI switch, you can use that to drop into ddb and then use 'x' to see who owns
> various mutexes (sched_lock and callout_mtx being the primary spin mutexes of
> concern).  If you compile your kernel with WITNESS and MUTEX_DEBUG, then you
> can use 'x' to look at the sched_lock and callout_mtx mutex structures, find
> the pointer to the mtx_debug structure, and examine that to find the mtxd_file
> and mtxd_line members.  Then you can look at those (x/s to look at the filename
> as a string) to find the filename and line number when the mutex was last
> acquired.  Grr, except that this is broken for spin mutexes.  If you are
> patient, you can try rigging up a serial console, compile KTR into your kernel
> as so:
> options KTR
> options KTR_EXTEND
> Then when the machine has booted, log in via ssh or a tty other than the serial
> console and type the following:
> # sysctl -w debug.ktr_mask=0x1208
> # sysctl -w debug.ktr_verbose=2
> # while (1) do
> > make -j 16 buildworld
> > end
> Unfortunately, there is a chance the machine will die before it hangs due to
> exceeding the stack space.  In that case, you can _try_ bumping UPAGES, but
> that didn't help on my test machines. :-/  However, if your machine doesn't
> blow up and die, then when it hangs, the KTR output dumped to the serial console
> (which you should probably log to a file via script or somesuch) will show what
> mutex was acquired and where it was acquired that is causing the hang.
> -- 
> John Baldwin <[EMAIL PROTECTED]> --
> PGP Key:
> "Power Users Use the Power to Serve!"  -

Marc G. Fournier                   ICQ#7615664               IRC Nick: Scrappy
Systems Administrator @ 
primary: [EMAIL PROTECTED]           secondary: scrappy@{freebsd|postgresql}.org 

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