From owner-cvs-src@FreeBSD.ORG Sun Aug 22 00:16:03 2004 Return-Path: Delivered-To: cvs-src@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 0097916A4CE; Sun, 22 Aug 2004 00:16:03 +0000 (GMT) Received: from cs.rice.edu (cs.rice.edu [128.42.1.30]) by mx1.FreeBSD.org (Postfix) with ESMTP id D8A2043D46; Sun, 22 Aug 2004 00:16:02 +0000 (GMT) (envelope-from alc@cs.rice.edu) Received: from localhost (calypso.cs.rice.edu [128.42.1.127]) by cs.rice.edu (Postfix) with ESMTP id 13BEB4ABB4; Sat, 21 Aug 2004 19:16:00 -0500 (CDT) Received: from cs.rice.edu ([128.42.1.30]) by localhost (calypso.cs.rice.edu [128.42.1.127]) (amavisd-new, port 10024) with LMTP id 31747-01-73; Sat, 21 Aug 2004 19:15:59 -0500 (CDT) Received: by cs.rice.edu (Postfix, from userid 19572) id B29A34ABB3; Sat, 21 Aug 2004 19:15:59 -0500 (CDT) Date: Sat, 21 Aug 2004 19:15:59 -0500 From: Alan Cox To: Brian Fundakowski Feldman Message-ID: <20040822001559.GG9106@cs.rice.edu> References: <200408211920.i7LJKLlA088634@repoman.freebsd.org> <20040821225939.GA784@green.homeunix.org> <20040821233134.GF9106@cs.rice.edu> <20040821234116.GC784@green.homeunix.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20040821234116.GC784@green.homeunix.org> User-Agent: Mutt/1.4.2i X-Virus-Scanned: by amavis-20030616-p7 at cs.rice.edu cc: Alan Cox cc: cvs-src@FreeBSD.org cc: src-committers@FreeBSD.org cc: cvs-all@FreeBSD.org Subject: Re: cvs commit: src/sys/vm vm_fault.c X-BeenThere: cvs-src@freebsd.org X-Mailman-Version: 2.1.1 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: Sun, 22 Aug 2004 00:16:03 -0000 On Sat, Aug 21, 2004 at 07:41:16PM -0400, Brian Fundakowski Feldman wrote: > On Sat, Aug 21, 2004 at 06:31:34PM -0500, Alan Cox wrote: > > On Sat, Aug 21, 2004 at 06:59:39PM -0400, Brian Fundakowski Feldman wrote: > > > On Sat, Aug 21, 2004 at 07:20:21PM +0000, Alan Cox wrote: > > > > alc 2004-08-21 19:20:21 UTC > > > > > > > > FreeBSD src repository > > > > > > > > Modified files: > > > > sys/vm vm_fault.c > > > > Log: > > > > Further reduce the use of Giant by vm_fault(): Giant is held only when > > > > manipulating a vnode, e.g., calling vput(). This reduces contention for > > > > Giant during many copy-on-write faults, resulting in some additional > > > > speedup on SMPs. > > > > > > > > Note: debug_mpsafevm must be enabled for this optimization to take effect. > > > > > > This is very broken. See included first attempt at fixing it without > > > regard for actually trying to reimplement debug.mpsafenet for vnodes. > > > > > > > Can you please explain what is broken? > > #1. Lock order reversal. Giant is acquired after the map read lock. No, that is the order it has been in for months. The other functions that acquire a map lock and Giant do the same. > #2. Unlocking Giant without it being locked. This occurs in both > VM_UNLOCK_GIANT() lines I removed. I know this because my machine > panicked on the other after I removed the first. Yes, I see what happened. I was able to reproduce it. As the commit explains, I failed to condition an early unlock of Giant on debug_mpsafevm. Regards, Alan