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From: Robert Watson <rwatson@FreeBSD.org>
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To: John Baldwin <jhb@FreeBSD.org>
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cc: William Michael Grim <wgrim@siue.edu>
Subject: Re: 4BSD Scheduler Problem on 5.3
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On Thu, 31 Mar 2005, John Baldwin wrote:

> On Thursday 31 March 2005 03:38 pm, William Michael Grim wrote:
> > Hello.
> >
> > I keep having kernel panics every couple weeks on my system.  It occurs in
> > the sched_switch() function.  There are several other statements in the
> > backtrace involving "??"; what are those?
> >
> > I have attached the dump output and system info to this email.  Any
> > feedback would be helpful.
> >
> > Thanks so much for your help.
> 
> The real trace ends with Xint0x80_syscall().  The rest after that is
> garbage memory.  Your real problem is in exit1() or ttywakeup().  Since
> ttywakeup() doesn't call exit1() (AFAIK), the exit1() frame is probably
> bogus (gdb doesn't grok trapframes maybe?) and the real bug is a NULL
> pointer deref in ttywakeup().  Perhaps it's a bug in the ptc driver? 
> (ptcopen is in the trace).  What is the ptc driver anyway? 

I think we have a race in -STABLE relating to tty wakeups and
open/close/device teardown.  I've seen a panic relating to sio during a
tty close on RELENG_5 about 5-6 months ago, but was unable to get a dump. 
Scott has since fixed dumps with twe, but I've not yet been able to get
the bug to recur.  I'll give it another try. 

Robert N M Watson