continuous backtrace ... ?

continuous backtrace ... ?

[Robert White]

Greetings,

I have a 2.5.70 kernel image which, at boot, goes into a continuously
looping backtrace.  It scrolls up the screen too fast and continuously to
read but it is clearly a backtrace. If I just relax and watch I can see the
[bracketed hex] and routine name shape of it whizzing by.

This happens while the file systems are read only and the system doesn't
respond to the keyboard at all.

Is there any good way to capture this stream of data in any kind of useful
way?  or at least pause the spew so that I can find the general locus of the
problem?

Given the immediacy of the problem (it appears just-about-concurrently with
attempt to draw the boot logo) I suspect that it has something to do with
the console driver (radeon frame buffer VGA console in normal mode)
interacting with my All-In-Wonder 9700 pro and the very new P4-3ghz in
hyperthreading mode.


Rob.

P.S. I realize suddenly that I should at least include the .config file but
the machine is at home and turned off just now... 8-)

Re: continuous backtrace ... ?

[Andreas Dilger]

On Jun 16, 2003  12:15 -0700, Robert White wrote:
> I have a 2.5.70 kernel image which, at boot, goes into a continuously
> looping backtrace.  It scrolls up the screen too fast and continuously to
> read but it is clearly a backtrace. If I just relax and watch I can see the
> [bracketed hex] and routine name shape of it whizzing by.
> 
> This happens while the file systems are read only and the system doesn't
> respond to the keyboard at all.
> 
> Is there any good way to capture this stream of data in any kind of useful
> way?  or at least pause the spew so that I can find the general locus of the
> problem?
> 
> Given the immediacy of the problem (it appears just-about-concurrently with
> attempt to draw the boot logo) I suspect that it has something to do with
> the console driver (radeon frame buffer VGA console in normal mode)
> interacting with my All-In-Wonder 9700 pro and the very new P4-3ghz in
> hyperthreading mode.

Probably a stack overflow.  Once you hit the do_IRQ() stack overflow
detection code, you get stuck in a loop because your console output is
slow enough that you immediately get another IRQ, rinse, repeat.

I fixed this locally by adding a static jiffies counter to rate-limit
the overflow stack dump to once per 5 seconds.  If you overflow your
stack more often than that, well too bad.  At least you have a chance
to look at your console instead of the machine essentially being wedged.

Cheers, Andreas
--
Andreas Dilger
http://sourceforge.net/projects/ext2resize/
http://www-mddsp.enel.ucalgary.ca/People/adilger/