From owner-cvs-src@FreeBSD.ORG Fri Oct 5 19:00:29 2007 Return-Path: Delivered-To: cvs-src@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id EF2B716A468; Fri, 5 Oct 2007 19:00:29 +0000 (UTC) (envelope-from jhb@freebsd.org) Received: from speedfactory.net (mail6.speedfactory.net [66.23.216.219]) by mx1.freebsd.org (Postfix) with ESMTP id 77C9913C46A; Fri, 5 Oct 2007 19:00:29 +0000 (UTC) (envelope-from jhb@freebsd.org) Received: from server.baldwin.cx (unverified [66.23.211.162]) by speedfactory.net (SurgeMail 3.8p) with ESMTP id 213082160-1834499 for multiple; Fri, 05 Oct 2007 15:00:18 -0400 Received: from localhost.corp.yahoo.com (john@localhost [127.0.0.1]) (authenticated bits=0) by server.baldwin.cx (8.13.8/8.13.8) with ESMTP id l95J03Il056520; Fri, 5 Oct 2007 15:00:03 -0400 (EDT) (envelope-from jhb@freebsd.org) From: John Baldwin To: Jeff Roberson Date: Fri, 5 Oct 2007 13:50:39 -0400 User-Agent: KMail/1.9.6 References: <200710032106.l93L65bv095725@repoman.freebsd.org> <200710041219.13202.jhb@freebsd.org> <20071004182759.U912@10.0.0.1> In-Reply-To: <20071004182759.U912@10.0.0.1> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200710051350.39581.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, 05 Oct 2007 15:00:03 -0400 (EDT) X-Virus-Scanned: ClamAV 0.88.3/4480/Fri Oct 5 10:51:39 2007 on server.baldwin.cx X-Virus-Status: Clean X-Spam-Status: No, score=-3.9 required=4.2 tests=ALL_TRUSTED,AWL,BAYES_00, SUBJ_HAS_SPACES autolearn=ham version=3.1.3 X-Spam-Checker-Version: SpamAssassin 3.1.3 (2006-06-01) on server.baldwin.cx Cc: cvs-src@freebsd.org, src-committers@freebsd.org, cvs-all@freebsd.org Subject: Re: cvs commit: src/sys/fs/devfs devfs_vnops.c src/sys/fs/fifofs fifo_vnops.c src/sys/kern uipc_usrreq.c vfs_vnops.c src/sys/vm vnode_pager.c X-BeenThere: cvs-src@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: CVS commit messages for the src tree List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 05 Oct 2007 19:00:30 -0000 On Thursday 04 October 2007 09:29:25 pm Jeff Roberson wrote: > On Thu, 4 Oct 2007, John Baldwin wrote: > > > On Wednesday 03 October 2007 07:48:00 pm Jeff Roberson wrote: > >> On Wed, 3 Oct 2007, John Baldwin wrote: > >> > >>> jhb 2007-10-03 21:06:05 UTC > >>> > >>> FreeBSD src repository > >>> > >>> Modified files: (Branch: RELENG_6) > >>> sys/fs/devfs devfs_vnops.c > >>> sys/fs/fifofs fifo_vnops.c > >>> sys/kern uipc_usrreq.c vfs_vnops.c > >>> sys/vm vnode_pager.c > >>> Log: > >>> MFC: Always use an exclusive lock on the leaf vnode during an open() when > >>> shared lookups are enabled. This closes a few races including a race > > where > >>> concurrent opens of a fifo could result in different v_fifoinfo > > structures > >>> in different threads. > >> > >> Long term we should really look for a better solution to this problem. > >> There are a number of was to improve snapshots in ffs by fixing shared > >> locking. > > > > I don't disagree. The fifo case can be fixed easily enough in the fifo code > > by using fifo_mtx to protect v_fifoinfo perhaps (or doing an upgrade on the > > vnode lock?), but for the MFC I didn't want to have to fix each of the races > > with open(2). Probably better to fix it more properly in HEAD first. > > Definitely someting for head. Were there any others that you ran into > besides v_fifoinfo? We should audit this more closely anyhow. I have > been reluctant to push too much shared locking into VFS because it's not > been so carefully studied. I just saw v_fifoinfo, but Pawel's original commit referenced updates to v_writecount, etc. The v_writecount one is in vn_open() itself: if ((error = VOP_OPEN(vp, fmode, cred, td, fp)) != 0) goto bad; if (fmode & FWRITE) vp->v_writecount++; *flagp = fmode; ASSERT_VOP_ELOCKED(vp, "vn_open_cred"); if (!mpsafe) VFS_UNLOCK_GIANT(vfslocked); return (0); If you just held a shared lock there, you could use atomic ops for vp->v_writecount (and still hold at least a shared vnode lock everywhere v_writecount is updated) and still be able to read vp->v_writecount safely while holding an exclusive lock on the vnode. -- John Baldwin