[PATCH 1/1] Fix bugs determining active VT consoles

[Joe Marcus Clarke]

On Fri, 2007-08-31 at 11:33 -0700, Remco Treffkorn wrote:
> On Friday 31 August 2007, Joe Marcus Clarke wrote:
> > On Fri, 2007-08-31 at 12:46 -0400, William Jon McCann wrote:
> > > On 8/31/07, Joe Marcus Clarke <marcus at freebsd.org> wrote:
> > > > On Fri, 2007-08-31 at 12:22 -0400, William Jon McCann wrote:
> > > > > On 8/30/07, Joe Marcus Clarke <marcus at freebsd.org> wrote:
> > > > > > On FreeBSD, having a process sit in VT_WAITACTIVE can cause kernel
> > > > > > panics or unkillable processes that consume 100% of the CPU.  To
> > > > > > work around this problem, replace the model where individual
> > > > > > threads call VT_WAITACTIVE with a g_timeout model which checks the
> > > > > > active VT every second, and queues an event when it changes.
> > > > >
> > > > > As I said in the other mail, I don't think we want to do this.  Can
> > > > > you describe why you think this isn't a FreeBSD kernel bug?
> > > >
> > > > I missed the other email, sorry.  From my reading of what this ioctl is
> > > > supposed to do, it is typically called after activating a given VT to
> > > > ensure that the VT is active before proceeding.  It should not be
> > > > something a program sits in for long periods of time.
> > >
> > > According to what or whom?
> >
> > I read it from Linux Journal:
> >
> > http://www.linuxjournal.com/article/2783
> >
> > That made me think it's used more to see if the switch is complete than
> > as an event driver.
> 
> This article is from 1994! Nowhere does it indicate a problem with 
> VT_WAITACTIVE.

No, but it indicates that the purpose of VT_WAITACTIVE is to wait for a
VT switch to complete.

> 
> How does this relate to FreeBSD and a potential problem there?

I already described the real problem with a process hanging on shutdown
because the threads are waiting for VT_WAITACTIVE to return.

> 
> Could you please explain what makes you think there is a FreeBSD bug that 
> makes VT_WAITACTIVE risky to use, and why you think working around a problem 
> is better than fixing it?

I already sent email out to kernel developers, but I haven't heard back.
Something needs to be done, and instead of sitting on my ass, I decided
to take some initiative based on what I found on the web.

Joe

-- 
Joe Marcus Clarke
FreeBSD GNOME Team      ::      gnome at FreeBSD.org
FreeNode / #freebsd-gnome
http://www.FreeBSD.org/gnome
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