From owner-freebsd-arch@FreeBSD.ORG  Mon Oct  4 18:26:25 2004
Return-Path: <owner-freebsd-arch@FreeBSD.ORG>
Delivered-To: freebsd-arch@freebsd.org
Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125])
	by hub.freebsd.org (Postfix) with ESMTP id C58AB16A4CE
	for <freebsd-arch@FreeBSD.org>; Mon,  4 Oct 2004 18:26:25 +0000 (GMT)
Received: from duchess.speedfactory.net (duchess.speedfactory.net
	[66.23.201.84])	by mx1.FreeBSD.org (Postfix) with SMTP id 6EE1B43D2D
	for <freebsd-arch@FreeBSD.org>; Mon,  4 Oct 2004 18:26:25 +0000 (GMT)
	(envelope-from ups@tree.com)
Received: (qmail 19133 invoked by uid 89); 4 Oct 2004 18:26:23 -0000
Received: from duchess.speedfactory.net (66.23.201.84)
  by duchess.speedfactory.net with SMTP; 4 Oct 2004 18:26:23 -0000
Received: (qmail 19102 invoked by uid 89); 4 Oct 2004 18:26:23 -0000
Received: from unknown (HELO palm.tree.com) (66.23.216.49)
  by duchess.speedfactory.net with SMTP; 4 Oct 2004 18:26:23 -0000
Received: from [127.0.0.1] (localhost.tree.com [127.0.0.1])
	by palm.tree.com (8.12.10/8.12.10) with ESMTP id i94IQNmt045033;
	Mon, 4 Oct 2004 14:26:23 -0400 (EDT)
	(envelope-from ups@tree.com)
From: Stephan Uphoff <ups@tree.com>
To: John Baldwin <jhb@FreeBSD.org>
In-Reply-To: <200410041321.45142.jhb@FreeBSD.org>
References: <1096610130.21577.219.camel@palm.tree.com>
	 <200410041321.45142.jhb@FreeBSD.org>
Content-Type: text/plain
Message-Id: <1096914383.44307.25.camel@palm.tree.com>
Mime-Version: 1.0
X-Mailer: Ximian Evolution 1.4.6 
Date: Mon, 04 Oct 2004 14:26:23 -0400
Content-Transfer-Encoding: 7bit
cc: Peter Holm <peter@holm.cc>
cc: Julian Elischer <julian@elischer.org>
cc: "freebsd-arch@freebsd.org" <freebsd-arch@FreeBSD.org>
Subject: Re: sched_switch (sched_4bsd) may be preempted
X-BeenThere: freebsd-arch@freebsd.org
X-Mailman-Version: 2.1.1
Precedence: list
List-Id: Discussion related to FreeBSD architecture
	<freebsd-arch.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-arch>,
	<mailto:freebsd-arch-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-arch>
List-Post: <mailto:freebsd-arch@freebsd.org>
List-Help: <mailto:freebsd-arch-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-arch>,
	<mailto:freebsd-arch-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Mon, 04 Oct 2004 18:26:25 -0000

On Mon, 2004-10-04 at 13:21, John Baldwin wrote:
> On Friday 01 October 2004 01:55 am, Stephan Uphoff wrote:
> > sched_switch (sched_4bsd) may be preempted in setrunqueue or slot_fill.
> > This could be ugly.
> > Wrapping it into a critical section and resetting TDP_OWEPREEMPT should
> > work.
> >
> > Hand trimmed patch:
> >
> > RCS file: /cvsroot/src/sys/kern/sched_4bsd.c,v
> > retrieving revision 1.65
> > diff -u -r1.65 sched_4bsd.c
> > --- sys/kern/sched_4bsd.c       16 Sep 2004 07:12:59 -0000      1.65
> > +++ sys/kern/sched_4bsd.c       1 Oct 2004 05:35:28 -0000
> > @@ -823,6 +823,7 @@
> >                 TD_SET_CAN_RUN(td);
> >         else {
> >                 td->td_ksegrp->kg_avail_opennings++;
> > +               critical_enter();
> >                 if (TD_IS_RUNNING(td)) {
> >                         /* Put us back on the run queue (kse and all).
> > */
> >                         setrunqueue(td, SRQ_OURSELF|SRQ_YIELDING);
> > @@ -834,6 +835,8 @@
> >                          */
> >                         slot_fill(td->td_ksegrp);
> >                 }
> > +               critical_exit();
> > +               td->td_pflags &= ~TDP_OWEPREEMPT;
> >         }
> >         if (newtd == NULL)
> >                 newtd = choosethread();
> 
> I thought that SRQ_YIELDING turned preempting off already.

Thanks - I missed that for setrunqueue.
However it is needed for maybe_preempt_in_ksegrp and slot_fill.
Guess adding a flag parameter and checking for SRQ_YIELDING for both
would be and easy way to get rid of the critical section hack.

	Stephan