kern/104406: [ufs] Processes get stuck in "ufs" state under persistent CPU load

[Alfred Perlstein]

* Oleg Derevenetz <oleg at vsi.ru> [071019 08:17] wrote:
> Hi all,
> 
> Can anyone take a look on PR kern/104406 ? I got repeatable hang situation, 
> but I can't obtain a kernel dump to get result of all show commands from 
> here:
> 
> http://www.freebsd.org/doc/en_US.ISO8859-1/books/developers-handbook/kerneldebug-deadlocks.html
> 
> After my break to debugger using Ctrl+Alt+Esc sequence and entering a 
> "panic" command kernel does not wrote a kernel dump but seems to hang. Can 
> anyone describe how to obtain a kernel dump in this situation, or at least 
> say - which output of show commands need in first place to debug this ? 
> Output of all suggested commands is huge and I afraid of making mistake 
> when carrying this output from screen to list of paper and back :-)

Oleg, one thing you can do to make this less painful is to
run your machine's console over serial port.

First get a crossover serial cable, make sure it works from one
box to another, it should be easy to run "tip com1" on both
boxes to ensure that it works.

Then you just need to add console=comconsole to /boot/loader.conf
and your box's console should come over serial.

Then on the machine watching the console, you can just do this:

% script
Script started, output file is typescript
% tip com1
...do ddb stuff now...
...stop tip
% exit

now you should have everything logged into a file called "typescript"
should save you a big headache.

As far as getting a dump from ddb, try this:

ddb> call doadump

I'm completely at a loss why this isn't a base ddb command "dump"
but whatever... :)

-Alfred