From owner-cvs-src@FreeBSD.ORG Mon Aug 9 19:15:01 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 CE70116A4D0 for ; Mon, 9 Aug 2004 19:15:01 +0000 (GMT) Received: from mail2.speakeasy.net (mail2.speakeasy.net [216.254.0.202]) by mx1.FreeBSD.org (Postfix) with ESMTP id A4BBC43D5D for ; Mon, 9 Aug 2004 19:15:01 +0000 (GMT) (envelope-from jhb@FreeBSD.org) Received: (qmail 18712 invoked from network); 9 Aug 2004 19:15:01 -0000 Received: from dsl027-160-063.atl1.dsl.speakeasy.net (HELO server.baldwin.cx) ([216.27.160.63]) (envelope-sender ) encrypted SMTP for ; 9 Aug 2004 19:15:01 -0000 Received: from 10.50.40.208 (gw1.twc.weather.com [216.133.140.1]) (authenticated bits=0) by server.baldwin.cx (8.12.11/8.12.11) with ESMTP id i79JEjHq076363; Mon, 9 Aug 2004 15:14:57 -0400 (EDT) (envelope-from jhb@FreeBSD.org) From: John Baldwin To: Alfred Perlstein Date: Mon, 9 Aug 2004 15:08:22 -0400 User-Agent: KMail/1.6 References: <200408042031.i74KVKUf039025@repoman.freebsd.org> <20040808042703.GA64746@xor.obsecurity.org> <20040808053321.GD57908@elvis.mu.org> In-Reply-To: <20040808053321.GD57908@elvis.mu.org> MIME-Version: 1.0 Content-Disposition: inline Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Message-Id: <200408091508.22530.jhb@FreeBSD.org> X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on server.baldwin.cx cc: cvs-src@FreeBSD.org cc: src-committers@FreeBSD.org cc: cvs-all@FreeBSD.org cc: Kris Kennaway Subject: Re: cvs commit: src/sys/i386/i386 pmap.c src/sys/kern subr_witness.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: Mon, 09 Aug 2004 19:15:01 -0000 On Sunday 08 August 2004 01:33 am, Alfred Perlstein wrote: > * Kris Kennaway [040807 21:28] wrote: > > On Wed, Aug 04, 2004 at 04:34:03PM -0400, John Baldwin wrote: > > > On Wednesday 04 August 2004 04:31 pm, John Baldwin wrote: > > > > jhb 2004-08-04 20:31:19 UTC > > > > > > > > FreeBSD src repository > > > > > > > > Modified files: > > > > sys/i386/i386 pmap.c > > > > sys/kern subr_witness.c > > > > Log: > > > > Remove a potential deadlock on i386 SMP by changing the lazypmap > > > > ipi and spin-wait code to use the same spin mutex (smp_tlb_mtx) as > > > > the TLB ipi and spin-wait code snippets so that you can't get into > > > > the situation of one CPU doing a TLB shootdown to another CPU that is > > > > doing a lazy pmap shootdown each of which are waiting on each other. > > > > With this change, only one of the CPUs would do an IPI and spin-wait > > > > at a time. > > > > > > Both this patch and the previous I have tested locally and also sent > > > out to current@ for testing. However, I received zero feedback (not > > > even useless feedback), so they may theoretically be risky. > > > > Isn't this the patch I tested for you and reported that it did not fix > > the problem? > > Y'know there's some existing research on these sort of low level > deadlocks, ie. how to do TLB shootdown without deadlock in: > > "UNIX Internals: The New Frontiers" Yes, and the failsafe algorithm is to halt all CPUs, do the change, then unhalt the CPUs forcing each one to do a TLB shootdown when it unfreezes. Unfortuantely, this has a very negative performance impact as the book also details. The current code was written by Peter who is not all that dumb, Alfred. -- John Baldwin <>< http://www.FreeBSD.org/~jhb/ "Power Users Use the Power to Serve" = http://www.FreeBSD.org