Crash dump problem - sleeping thread owns a non-sleepable lock during crash dump write

[Terry Kennedy]

> > The crash was a "page fault while in kernel mode" with the current process
> > being the interrupt service routine for the bce0 GigE. Things progressed
> > reasonably until partway through the dump, when the system locked up with a
> > "Sleeping thread (tid 100028, pid 12) owns a non-sleepable lock". That's the
> > same PID as reported in the main crash.
>
> Hmm.  You could try changing the code to not do a nested panic in that
> case.  You would update subr_turnstile.c to just return if panicstr is
> not NULL rather than calling panic.  However, there is still a good
> chance you will end up deadlocking in that case.  I have another patch I
> can send you next week that prevents blocking on mutexes duing a panic
> which may also help.

  Ok, I'll be glad to try that.

> > 3) Is there any way to rig the system to obtain more info if this happens
> > again? Right now I'm using an embedded remote console server, but I could
> > switch the system to a serial port if enabling the kernel debugger might help.
> > But I think that the sleeping thread bit would happen even at the debugger
> > prompt, wouldn't it?
>
> Include DDB and enable the 'trace_on_panic' sysctl knob perhaps.

  Hmmm. Do you think it will get very far before the sleeping thread business
locks it up?

> > Is it possible to correlate the source line in the kernel with the instruction
> > pointer in the panic?
>
> If you are booted into the same kernel with the same modules loaded, you
> can probably run 'kgdb' as root do 'l *<instruction pointer>'.

  I did that and discovered that the 0x20: prefix is probably unwanted:

(kgdb) l *0x20:0xffffffff801e3c06
A syntax error in expression, near `:0xffffffff801e3c06'.
(kgdb) l *0xffffffff801e3c06
0xffffffff801e3c06 is in bce_start_locked (/usr/src/sys/dev/bce/if_bce.c:6996).
6991                    }
6992
6993                    count++;
6994
6995                    /* Send a copy of the frame to any BPF listeners. */
6996                    ETHER_BPF_MTAP(ifp, m_head);
6997            }
6998
6999            /* Exit if no packets were dequeued. */
7000            if (count == 0) {
(kgdb) 

  This kernel does have BPF compiled in, but I don't think it was in use at
the time. 

  Any further suggestions to look at (remember, this system is in another
state from me and all I have is remote access to the framebuffer - I'd have
to go there and set up a serial console to be able to talk to the debugger
if it crashes).

	Thanks,
        Terry Kennedy             http://www.tmk.com
        terry at tmk.com             New York, NY USA