scheduler (sched_4bsd) questions

[Stephan Uphoff]

On Sun, 2004-10-10 at 15:57, Peter Holm wrote:
> On Sun, Oct 10, 2004 at 03:50:08PM -0400, Stephan Uphoff wrote:
> > On Tue, 2004-10-05 at 09:03, Peter Holm wrote: 
> > > On Mon, Oct 04, 2004 at 12:42:53PM -0700, Julian Elischer wrote:
> > > 
> > > OK, I got a crash dump now, after a few modifications to kern_shutdown.c
> > > 
> > > There are however a few strange things worth noticing:
> > > 
> > > 1) The are no panic string:
> > > 
> > > Mounted root from ufs:/dev/ad0s1a.
> > > pid 1146: corrected slot count (2->1)
> > > [thread 100796]
> > > Stopped at      sched_add+0x13: movl    0x14c(%esi),%ebx
> > > 
> > > 2) The gdb stack trace gets a bit weird at:
> > > 
> > > #8  0xc07812da in calltrap () at ../../../i386/i386/exception.s:140
> > > #9  0xc05f0018 in flock (td=0x0, uap=0x0) at ../../../kern/kern_descrip.c:2138
> > > #10 0xc0619fd1 in setrunqueue (td=0xc2319180, flags=0x0) at kern_switch.c:521
> > > #11 0xc061921f in sched_wakeup (td=0xc2319180) at ../../../kern/sched_4bsd.c:859
> > > 
> > > Where did flock() come from?
> > > 
> > > The full console output is at http://www.holm.cc/stress/log/cons82.html
> > > 
> > > - Peter
> > 
> > I am still puzzled.
> > My newest pet theory is that the sorting of the kg_runq is corrupted
> > before setrunqueue is called.
> > Directly changing td_priority while the thread is on the run queue would
> > be an explanation.
> > However the only instance that I found is what I think is a rare
> > condition where sleepq_resume_thread may be called while the thread is
> > on a runqueue. (John - what did I miss this time ...)
> > 
> > Peter could you try this patch?
> > 
> 
> Sure, no problem.
> 
> This patch + your previous changes applied to HEAD, right?
> 
> - Peter

Yes.

I will try to clean up the old patches tonight to get them reviewed.

	Stephan


> 
> > Index: subr_sleepqueue.c
> > ===================================================================
> > RCS file: /cvsroot/src/sys/kern/subr_sleepqueue.c,v
> > retrieving revision 1.11
> > diff -u -r1.11 subr_sleepqueue.c
> > --- subr_sleepqueue.c   19 Aug 2004 11:31:41 -0000      1.11
> > +++ subr_sleepqueue.c   10 Oct 2004 18:18:55 -0000
> > @@ -642,7 +642,7 @@
> >         /* Adjust priority if requested. */
> >         MPASS(pri == -1 || (pri >= PRI_MIN && pri <= PRI_MAX));
> >         if (pri != -1 && td->td_priority > pri)
> > -               td->td_priority = pri;
> > +               sched_prio(td, pri);
> >         setrunnable(td);
> >         mtx_unlock_spin(&sched_lock);
> > }
> > 
> > Should it crash again could you walk the kg_runq to verify the sorting?
> > 
> > Thanks
> > 	Stephan
> > 
> > 
> > 
> >