Apache-worker stuck at 100% CPU

[Ivan Voras]

2008/9/12 Alfred Perlstein <alfred at freebsd.org>:

> Try using "pstack" a few times.  It's in ports.
>
> Also, gcore(1) might help.

Will try.

> You can also try to attach using gdb.

I did, but either I'm missing something or I'm not using it well,
because I can't get a backtrace. How do I select threads to backtrace?
How do I pick what thread to backtrace?

> Basically, one of these tools should give you a stack trace which
> can help.
>
> It's interesting that the process is in "umtxn" though, is it
> multithreaded apache?  Can you dump the threads?  I think top(1)
> has an option to view each thread, how about trying that?

Yes, it's multithreaded apache. This did help somewhat - when I do it
I see that it's not actually stuck in umtxn - there's one thread that
consumes the CPU and it's apparently always running (in state CPUx).

  PID USERNAME PRI NICE   SIZE    RES STATE  C   TIME   WCPU COMMAND
 7212 www      103    0 30340K  7932K CPU2   2 444:23 99.02% httpd

I'm currently upgrading the system to 7-STABLE, to see if it helps.