From owner-svn-src-all@FreeBSD.ORG Thu Oct 1 13:21:36 2009 Return-Path: Delivered-To: svn-src-all@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id D0A79106568F; Thu, 1 Oct 2009 13:21:36 +0000 (UTC) (envelope-from asmrookie@gmail.com) Received: from mail-fx0-f222.google.com (mail-fx0-f222.google.com [209.85.220.222]) by mx1.freebsd.org (Postfix) with ESMTP id E3C4B8FC15; Thu, 1 Oct 2009 13:21:35 +0000 (UTC) Received: by fxm22 with SMTP id 22so129721fxm.36 for ; Thu, 01 Oct 2009 06:21:35 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:sender:received:in-reply-to :references:date:x-google-sender-auth:message-id:subject:from:to:cc :content-type; bh=XkSOXWfuEm4u1sOMwrPwvLGt7eAX+OEtyUtLObuxMZU=; b=DAMXioZJ8IDiBKV5o7mjAF8WPoxRRNvfb0TS6WHmZvKyv5QJ/QkSVuX9V6sQmEJFM+ 8NjfmWNpmd59UXQ52T6BV1c3lnEXRrLUXIP29KuKsiut5n7Z7/1LOA9YiVom3YKtBftD fRgsyt0fXsdiQva2IwCoqAYnN6H75v+PppCLc= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:sender:in-reply-to:references:date :x-google-sender-auth:message-id:subject:from:to:cc:content-type; b=AvnJBWNomNWi3KEOmunpNcA9LRogBF/ZDHpiJvH++B8+EIGXY7gh7Ou8RDmXtKnblI 0nFBnPg0PDtzTphR+h36lUg/0qaLo3Wm4yM/gqV4UNGjTlEsUMVo7TabfHqM6bOI1lOJ nHDV8NKYMDjd47KFkluRdFrb265BBUJELT73g= MIME-Version: 1.0 Sender: asmrookie@gmail.com Received: by 10.223.3.137 with SMTP id 9mr332980fan.45.1254403294882; Thu, 01 Oct 2009 06:21:34 -0700 (PDT) In-Reply-To: References: <200909301326.n8UDQVB1016396@svn.freebsd.org> Date: Thu, 1 Oct 2009 15:21:34 +0200 X-Google-Sender-Auth: 3e6186589986e703 Message-ID: <3bbf2fe10910010621u72d0f692h8f9c4a783667253d@mail.gmail.com> From: Attilio Rao To: Robert Watson Content-Type: text/plain; charset=UTF-8 Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org Subject: Re: svn commit: r197643 - in head/sys: kern sys X-BeenThere: svn-src-all@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: "SVN commit messages for the entire src tree \(except for " user" and " projects" \)" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 01 Oct 2009 13:21:36 -0000 2009/9/30 Robert Watson : > On Wed, 30 Sep 2009, Attilio Rao wrote: > >> When releasing a read/shared lock we need to use a write memory barrier >> in order to avoid, on architectures which doesn't have strong ordered >> writes, CPU instructions reordering. > > Hi Attilio (Fabio, et al), > > Nice catch! Are we aware of specific reported problems that can be laid at > the feet of this bug, or was this more of a "wait a moment, shouldn't there > be a barrier there?". Could you comment on the scope of this problem across > architectures we support? A possible problem related to that would be MD specific and not on ia32/amd64 because there the barriers and simple atomics are the same. Given that sun4v suffers of serveral other problems, that MIPS has no SMP support, you would find it only for arm, ia64 and sparc eventually. Thus I'm not aware of any problem which can be reconducted to that. Attilio -- Peace can only be achieved by understanding - A. Einstein