Received: with ECARTIS (v1.0.0; list xfs); Mon, 25 Aug 2008 18:54:37 -0700 (PDT) X-Spam-Checker-Version: SpamAssassin 3.3.0-r574664 (2007-09-11) on oss.sgi.com X-Spam-Level: X-Spam-Status: No, score=-2.5 required=5.0 tests=AWL,BAYES_00 autolearn=ham version=3.3.0-r574664 Received: from cuda.sgi.com (cuda2.sgi.com [192.48.168.29]) by oss.sgi.com (8.12.11.20060308/8.12.11/SuSE Linux 0.7) with ESMTP id m7Q1sUEX012342 for ; Mon, 25 Aug 2008 18:54:31 -0700 X-ASG-Debug-ID: 1219715752-4cf603540000-NocioJ X-Barracuda-URL: http://cuda.sgi.com:80/cgi-bin/mark.cgi Received: from ipmail01.adl6.internode.on.net (localhost [127.0.0.1]) by cuda.sgi.com (Spam Firewall) with ESMTP id 0DC713CD48C for ; Mon, 25 Aug 2008 18:55:53 -0700 (PDT) Received: from ipmail01.adl6.internode.on.net (ipmail01.adl6.internode.on.net [203.16.214.146]) by cuda.sgi.com with ESMTP id Dv77OX9UipMuZOGW for ; Mon, 25 Aug 2008 18:55:53 -0700 (PDT) X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: AtACAPz8skh5LD0wiGdsb2JhbACSLAEBAQ8gpC+Baw X-IronPort-AV: E=Sophos;i="4.32,266,1217773800"; d="scan'208";a="180299290" Received: from ppp121-44-61-48.lns10.syd7.internode.on.net (HELO disturbed) ([121.44.61.48]) by ipmail01.adl6.internode.on.net with ESMTP; 26 Aug 2008 11:25:50 +0930 Received: from dave by disturbed with local (Exim 4.69) (envelope-from ) id 1KXnmf-0005NY-Ah; Tue, 26 Aug 2008 11:55:49 +1000 Date: Tue, 26 Aug 2008 11:55:49 +1000 From: Dave Chinner To: Peter Zijlstra Cc: Lachlan McIlroy , Daniel J Blueman , Linux Kernel , xfs@oss.sgi.com, hch@lst.de X-ASG-Orig-Subj: Re: [2.6.27-rc4] XFS i_lock vs i_iolock... Subject: Re: [2.6.27-rc4] XFS i_lock vs i_iolock... Message-ID: <20080826015549.GT5706@disturbed> Mail-Followup-To: Peter Zijlstra , Lachlan McIlroy , Daniel J Blueman , Linux Kernel , xfs@oss.sgi.com, hch@lst.de References: <6278d2220808221412x28f4ac5dl508884c8030b364a@mail.gmail.com> <20080825010213.GO5706@disturbed> <48B21507.9050708@sgi.com> <20080825035542.GR5706@disturbed> <1219647573.20732.28.camel@twins> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1219647573.20732.28.camel@twins> User-Agent: Mutt/1.5.18 (2008-05-17) X-Barracuda-Connect: ipmail01.adl6.internode.on.net[203.16.214.146] X-Barracuda-Start-Time: 1219715754 X-Barracuda-Bayes: INNOCENT GLOBAL 0.0000 1.0000 -2.0210 X-Barracuda-Virus-Scanned: by cuda.sgi.com at sgi.com X-Barracuda-Spam-Score: -2.02 X-Barracuda-Spam-Status: No, SCORE=-2.02 using per-user scores of TAG_LEVEL=2.0 QUARANTINE_LEVEL=1000.0 KILL_LEVEL=2.1 tests= X-Barracuda-Spam-Report: Code version 3.2, rules version 3.2.1.3728 Rule breakdown below pts rule name description ---- ---------------------- -------------------------------------------------- X-Virus-Scanned: ClamAV 0.91.2/8088/Mon Aug 25 13:49:45 2008 on oss.sgi.com X-Virus-Status: Clean X-archive-position: 17716 X-ecartis-version: Ecartis v1.0.0 Sender: xfs-bounce@oss.sgi.com Errors-to: xfs-bounce@oss.sgi.com X-original-sender: david@fromorbit.com Precedence: bulk X-list: xfs On Mon, Aug 25, 2008 at 08:59:33AM +0200, Peter Zijlstra wrote: > On Mon, 2008-08-25 at 13:55 +1000, Dave Chinner wrote: > > On Mon, Aug 25, 2008 at 12:12:23PM +1000, Lachlan McIlroy wrote: > > > Dave Chinner wrote: > > >> On Fri, Aug 22, 2008 at 10:12:59PM +0100, Daniel J Blueman wrote: > > >>> ======================================================= > > >>> [ INFO: possible circular locking dependency detected ] > > >>> 2.6.27-rc4-224c #1 > > >>> ------------------------------------------------------- > > >>> xfs_fsr/5763 is trying to acquire lock: > > >>> (&(&ip->i_lock)->mr_lock/2){--..}, at: [] xfs_ilock+0x8c/0xb0 > > >>> > > >>> but task is already holding lock: > > >>> (&(&ip->i_iolock)->mr_lock/3){--..}, at: [] > > >>> xfs_ilock+0xa5/0xb0 > > >> > > >> False positive. We do: > > >> > > >> xfs_lock_two_inodes(ip, tip, XFS_IOLOCK_EXCL | XFS_ILOCK_EXCL); > > > > > > Why not just change the above line to two lines: > > > xfs_lock_two_inodes(ip, tip, XFS_IOLOCK_EXCL); > > > xfs_lock_two_inodes(ip, tip, XFS_ILOCK_EXCL); > > > > Yeah, that'd work, but it implllies that we no longer allow > > xfs_lock_two_inodes() to take both inode locks at once. > > How can you take two locks in one go? It seems to me you always need to > take them one after another, and as soon as you do that, you have > ordering constraints. It doesn't take them both inode locks in one go - it does them separately in a given order via xfs_ilock(). Basically there are two layers of constraints here - xfs_ilock() handles the order withing a given inode, xfs_lock_two_inodes() handles order and deadlock prevention between inodes. What lockdep is complaining about is a difference in the lock order between different locks in different inodes - a situation that does not result in a deadlock... Cheers, Dave. -- Dave Chinner david@fromorbit.com