Crash with FreeBSD 6.1 STABLE of today

[Gavin Atkinson]

On Mon, 2006-06-26 at 15:15 +0200, Martin Blapp wrote:
> A remote stress testing of a tty session over serial cable
> with a patched kernel worked fine.
> 
> How to proceed now ? The patch also applies to CURRENT
> as there where no big changes since the repo has been
> branched.
> 
> Should I commit it to CURRENT ?
> 
> > http://mx.imp.ch/patch-tty.t_pgrp.diff

I'm still not convinced that the proctree lock is the correct lock to
use - maybe a new lock for the tty subsystem?  Also, some of the locking
in the patch appears to be unnecessary.  I can't help feeling that this
patch is the heavy-handed solution to the problem, and given how
heavyweight locks can be, maybe it's not a good solution.

Is the problem actually understood?  Do we know what's racing with what?
Given there only ever seems to be a single backtrace involved, as far as
I can tell, it's ttymodem racing with tty_close - can those two
functions alone be locked?

Alas, I can't recreate the problem on-demand so can't really find a
better solution.

Gavin