Re: [9fans] crashing 9vx

[erik quanstrom <quanstro@quanstro.net>]

On Sun May 30 12:00:25 EDT 2010, xigh@bouyapop.org wrote:
> You also have to recompile vx library.
>
> Phil
>
> Brian L. Stuart wrote:
> >> OK, somebody sent a hint that it
> >> might make sense to take the -O3 out
> >> of the make flags. Done.
> >>
> >> Result: I can now get through this command:
> >> hget -v http://plan9.bell-labs.com/plan9/download/plan9.iso.bz2>/tmp/iso.bz2
> >> |[2]aux/statusbar plan9.iso
> >>
> >> without an explosion.
> >>
> >
> > This is weird.  I just built 9vx on FreeBSD without
> > the -O3.  But instead of being more stable, that
> > one crashed on startup, like Charles reported.
> > Namely:
> >
> > 9vx panic: user fault: signo=11 addr=3850cb67 [useraddr=cb67] read=1 eip=80b973c esp=493ffac0
> > aborting, to dump core.
> >
> > With the -O3, the crashes are rare, and seem to be
> > associated with heavy I/O.

you may be right, but it seems too easy to blame gcc.
a better fit for the facts so far would seem to me that
9vx' locking is broken.  the optimization may just put
more pressure on broken locking.

putting a couple of prints in the startup will also change
timing.  if you can eliminate or cause a crash by adding
or removing prints, then you can be sure that there is a
locking/timing problem in 9vx.  although that doesn't prove
that gcc is blameless, it would be a reasonable assumption.

- erik