From owner-p4-projects@FreeBSD.ORG Fri Aug 11 16:56:28 2006 Return-Path: X-Original-To: p4-projects@freebsd.org Delivered-To: p4-projects@freebsd.org Received: by hub.freebsd.org (Postfix, from userid 32767) id C262316A4E6; Fri, 11 Aug 2006 16:56:28 +0000 (UTC) X-Original-To: perforce@freebsd.org Delivered-To: perforce@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 9D20216A4DD; Fri, 11 Aug 2006 16:56:28 +0000 (UTC) (envelope-from jhb@freebsd.org) Received: from server.baldwin.cx (66-23-211-162.clients.speedfactory.net [66.23.211.162]) by mx1.FreeBSD.org (Postfix) with ESMTP id 12B8C43D70; Fri, 11 Aug 2006 16:56:23 +0000 (GMT) (envelope-from jhb@freebsd.org) Received: from localhost.corp.yahoo.com (john@localhost [127.0.0.1]) (authenticated bits=0) by server.baldwin.cx (8.13.6/8.13.6) with ESMTP id k7BGuIbr082536; Fri, 11 Aug 2006 12:56:23 -0400 (EDT) (envelope-from jhb@freebsd.org) From: John Baldwin To: Divacky Roman Date: Fri, 11 Aug 2006 12:49:44 -0400 User-Agent: KMail/1.9.1 References: <200608111110.k7BBAxIO059339@repoman.freebsd.org> <20060811124027.K45647@fledge.watson.org> <20060811121314.GA85207@stud.fit.vutbr.cz> In-Reply-To: <20060811121314.GA85207@stud.fit.vutbr.cz> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200608111249.44686.jhb@freebsd.org> X-Greylist: Sender succeeded SMTP AUTH authentication, not delayed by milter-greylist-2.0.2 (server.baldwin.cx [127.0.0.1]); Fri, 11 Aug 2006 12:56:23 -0400 (EDT) X-Virus-Scanned: ClamAV 0.87.1/1646/Fri Aug 11 05:51:17 2006 on server.baldwin.cx X-Virus-Status: Clean X-Spam-Status: No, score=-4.4 required=4.2 tests=ALL_TRUSTED,AWL,BAYES_00 autolearn=ham version=3.1.0 X-Spam-Checker-Version: SpamAssassin 3.1.0 (2005-09-13) on server.baldwin.cx Cc: Roman Divacky , Perforce Change Reviews , Robert Watson Subject: Re: PERFORCE change 103633 for review X-BeenThere: p4-projects@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: p4 projects tree changes List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 11 Aug 2006 16:56:29 -0000 On Friday 11 August 2006 08:13, Divacky Roman wrote: > On Fri, Aug 11, 2006 at 12:42:50PM +0100, Robert Watson wrote: > > On Fri, 11 Aug 2006, Roman Divacky wrote: > > > > >http://perforce.freebsd.org/chv.cgi?CH=103633 > > > > > >Change 103633 by rdivacky@rdivacky_witten on 2006/08/11 11:10:09 > > > > > > Giantify futex code - this is necessary because the futex code is > > > expected to be atomic. > > > I need to assure the atomicity. I am using Giant because its > > > sleepable mutex. I hope > > > someone will point me to some other better solution. > > > > Giant is not "sleepable" in the same sense that sx locks, lockmgr locks, > > etc, are. Normally "sleepable" means that the lock can be held across a > > sleep of potentially unbounded length, such as msleep(), tsleep(), > > cv_wait(), etc. Giant is automatically dropped by the kernel on sleep, and > > re-acquired one wakeup. This means that Giant does not provide mutual > > exclusion across a sleep -- if this is a property you are relying on, then > > Giant is not what you want. If you most sleep while holding a lock, I > > would recommend an sx lock. However, a preferred solution is not to sleep > > holding a lock. > > yes... sleepable as in "can be held while sleeping no matter how this is acomplished" > > I think the main problem (which is now fixed) was with this: > > copyin(addr, val1); > if (val1 == val2) > .... > > being non-atomic. On the other hand I tried to use other locks other then Giant and it > didnt work. I hope to investigate that later. Now I have this working and my focus is elsewhere. No, what you have done is wrong. The idea of doing copyin() and then compare is just plain not going to work. :) You will need to use casuptr() or the like similar to the umtx code. This is assuming that a futex can be manipulated from userland w/o entering the kernel. -- John Baldwin