From owner-freebsd-arch@FreeBSD.ORG Mon Oct 4 19:14:13 2004 Return-Path: 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 DD3FA16A4CE for ; Mon, 4 Oct 2004 19:14:12 +0000 (GMT) Received: from relay.pair.com (relay.pair.com [209.68.1.20]) by mx1.FreeBSD.org (Postfix) with SMTP id 7D89943D41 for ; Mon, 4 Oct 2004 19:14:12 +0000 (GMT) (envelope-from pho@holm.cc) Received: (qmail 78180 invoked from network); 4 Oct 2004 19:14:11 -0000 Received: from 0x50a43fc7.hknxx1.adsl-dhcp.tele.dk (HELO peter.osted.lan) (80.164.63.199) by relay.pair.com with SMTP; 4 Oct 2004 19:14:11 -0000 X-pair-Authenticated: 80.164.63.199 Received: from peter.osted.lan (localhost.osted.lan [127.0.0.1]) by peter.osted.lan (8.12.10/8.12.10) with ESMTP id i94JEAEe008457; Mon, 4 Oct 2004 21:14:10 +0200 (CEST) (envelope-from pho@peter.osted.lan) Received: (from pho@localhost) by peter.osted.lan (8.12.10/8.12.10/Submit) id i94JEAd1008456; Mon, 4 Oct 2004 21:14:10 +0200 (CEST) (envelope-from pho) Date: Mon, 4 Oct 2004 21:14:10 +0200 From: Peter Holm To: Julian Elischer Message-ID: <20041004191410.GA8423@peter.osted.lan> References: <1095468747.31297.241.camel@palm.tree.com> <1096496057.3733.2163.camel@palm.tree.com> <1096603981.21577.195.camel@palm.tree.com> <200410041131.35387.jhb@FreeBSD.org> <1096911278.44307.17.camel@palm.tree.com> <20041004184939.GA8178@peter.osted.lan> <41619D29.1000704@elischer.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <41619D29.1000704@elischer.org> User-Agent: Mutt/1.4.1i cc: Peter Holm cc: "freebsd-arch@freebsd.org" cc: Stephan Uphoff Subject: Re: scheduler (sched_4bsd) questions X-BeenThere: freebsd-arch@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list List-Id: Discussion related to FreeBSD architecture List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 04 Oct 2004 19:14:13 -0000 On Mon, Oct 04, 2004 at 11:57:45AM -0700, Julian Elischer wrote: > can you run ktrdump against teh corefile and get the ktr output? > (you do have it enabled right?) > No, that's one of the problems: doadump() fails with this specific panic. - Peter > > Peter Holm wrote: > > >On Mon, Oct 04, 2004 at 01:34:38PM -0400, Stephan Uphoff wrote: > > > > > >>On Mon, 2004-10-04 at 11:31, John Baldwin wrote: > >> > >> > >>>On Friday 01 October 2004 12:13 am, Stephan Uphoff wrote: > >>> > >>> > >>>>On Wed, 2004-09-29 at 18:14, Stephan Uphoff wrote: > >>>> > >>>> > >>>>>I was looking at the MUTEX_WAKE_ALL undefined case when I used the > >>>>>critical section for turnstile_claim(). > >>>>>However there are bigger problems with MUTEX_WAKE_ALL undefined > >>>>>so you are right - the critical section for turnstile_claim is pretty > >>>>>useless. > >>>>> > >>>>> > >>>>Arghhh !!! > >>>> > >>>>MUTEX_WAKE_ALL is NOT an option in GENERIC. > >>>>I recall verifying that it is defined twice. Guess I must have looked at > >>>>the wrong source tree :-( > >>>>This means yes - we have bigger problems! > >>>> > >>>>Example: > >>>> > >>>>Thread A holds a mutex x contested by Thread B and C and has priority > >>>>pri(A). > >>>> > >>>>Thread C holds a mutex y and pri(B) < pri(C) > >>>> > >>>>Thread A releases the lock wakes thread B but lets C on the turnstile > >>>>wait queue. > >>>> > >>>>An interrupt thread I tries to lock mutex y owned by C. > >>>> > >>>>However priority inheritance does not work since B needs to run first to > >>>>take ownership of the lock. > >>>> > >>>>I is blocked :-( > >>>> > >>>> > >>>Ermm, if the interrupt happens after x is released then I's priority > >>>should propagate from I to C to B. > >>> > >>> > >>There is a hole after the mutex x is released by A - but before B can > >>claim the mutex. The turnstile for mutex x is unowned and interrupt > >>thread I when trying to donate its priority will run into: > >> > >> if (td == NULL) { > >> /* > >> * This really isn't quite right. Really > >> * ought to bump priority of thread that > >> * next acquires the lock. > >> */ > >> return; > >> } > >> > >>So B needs to run and acquire the mutex before priority inheritance > >>works again and does not get a priority boost to do so. > >> > >>This is easy to fix and MUTEX_WAKE_ALL can be removed again at that time > >>- but my time budget is limited and Peter has an interesting bug left > >>that has priority. > >> > >> > > > >I'm not closer to being able to create this panic in a controlled way. > >After a whole day of different tests I finally got this panic: > >http://www.holm.cc/stress/log/cons81.html. The trigger seems to be one > >particular Java applet, but it is not easily reproduceable. > > > >- Peter > > > > > > > >>>If the interrupt happens before x is released, > >>>then the final bit of propagate_priority() should handle it since it > >>>resorts the turnstile's thread queue so that C will be awakened rather > >>>than B. > >>> > >>> > >>Agreed. > >> > >> Stephan > >> > >> > >_______________________________________________ > >freebsd-arch@freebsd.org mailing list > >http://lists.freebsd.org/mailman/listinfo/freebsd-arch > >To unsubscribe, send any mail to "freebsd-arch-unsubscribe@freebsd.org" > > > > -- Peter Holm