scheduler (sched_4bsd) questions

[Peter Holm]

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

> 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
> 
> 
> 
> 

-- 
Peter Holm