Re: How to debug hanging machines / proc: table is full

On Wed, Jul 31, 2019 at 05:46:08PM +0200, Raimo Niskanen wrote:
> I have enabled Witness, it went so-so. We'll see what it catches.
>
> I downloaded 6.5 amd64 src.tar.gz and sys.tar.gz, unpacked them,
> applied all patches for stable 001-006 and built a kernel with:
> include "arch/amd64/conf/GENERIC"
> option MULTIPROCESSOR
> option MP_LOCKDEBUG
> option WITNESS
>
> Then I activated in /etc/sysctl.conf:
> ddb.console=1
> kern.witness.locktrace=1
> kern.witness.watch=3
>
> For fun, I pressed Ctrl+Alt+Esc at the console, got a ddb> prompt and typed
> "show witness". It printed lots of info, I scrolled down to the end, but
> during the printout there was an UVM fault:
>
> Spin locks:
> /usr/src/sys/....
> :
> bla bla bla
> :
> uvm_fault(0xffffffff81e03b50, 0xffff800022368360, 0, 1) -> e
> kernel: page fault trap, code=0
> Faulted in DDB: continuing...

The output of "show witness" is unlikely to be useful in your case.
It is more of a tool for debugging witness. You can ignore it.
However, "show all locks" might display interesting information
after a witness-related panic.