From owner-svn-src-all@FreeBSD.ORG  Sun Mar 29 21:15:44 2015
Return-Path: <owner-svn-src-all@FreeBSD.ORG>
Delivered-To: svn-src-all@freebsd.org
Received: from mx1.freebsd.org (mx1.freebsd.org
 [IPv6:2001:1900:2254:206a::19:1])
 (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits))
 (No client certificate requested)
 by hub.freebsd.org (Postfix) with ESMTPS id 6D4A92CF;
 Sun, 29 Mar 2015 21:15:44 +0000 (UTC)
Received: from mail-ig0-x229.google.com (mail-ig0-x229.google.com
 [IPv6:2607:f8b0:4001:c05::229])
 (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits))
 (Client CN "smtp.gmail.com",
 Issuer "Google Internet Authority G2" (verified OK))
 by mx1.freebsd.org (Postfix) with ESMTPS id 2E452AC3;
 Sun, 29 Mar 2015 21:15:44 +0000 (UTC)
Received: by igbud6 with SMTP id ud6so58411783igb.1;
 Sun, 29 Mar 2015 14:15:43 -0700 (PDT)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113;
 h=mime-version:sender:in-reply-to:references:date:message-id:subject
 :from:to:cc:content-type;
 bh=0e8lI/A0F8Hv6WZNdHEKDWa5uzQjrcSrGcnRVdGTQuw=;
 b=YBZyNEJkL3krtOReuqym85sw4JFl58920FAyBx3cvhScOhMdkGZSH5J/EKnGtSS8ph
 Yq8R5IsUTJqbTiGiVDB5wfL89HjIqAVHAMhIHG1+mZUiiYEowDD6Weu6ldFnDVjt0j7d
 pwSaNEdZkQYy0kePd/YRDvAJxc1qok1YmfRGNh0LQ3eGGXx+ibkEATtgWDTm6mQOKKrH
 BhnWZFLe6PDN7P9Hq1CTlsMvFIvubknLj0cjShET3rOEk7KNmv5+qPa7XsnQ5vm8dksJ
 N2SXjdyaNHphblSEbDn7D5pXIbnGmKfCbZERICItBwvpP1kBcFCdflZ3k/VEOA0DFE7h
 sYag==
MIME-Version: 1.0
X-Received: by 10.107.155.13 with SMTP id d13mr43883951ioe.29.1427663743514;
 Sun, 29 Mar 2015 14:15:43 -0700 (PDT)
Sender: adrian.chadd@gmail.com
Received: by 10.36.17.194 with HTTP; Sun, 29 Mar 2015 14:15:43 -0700 (PDT)
In-Reply-To: <20150329210757.GA64665@FreeBSD.org>
References: <201503271326.t2RDQxd3056112@svn.freebsd.org>
 <20150328083443.GV64665@FreeBSD.org>
 <20150328191629.GY64665@FreeBSD.org> <5517B433.5010508@selasky.org>
 <CAJ-VmonU15_nEGVQNwR52deDf1TbPUz0oAMr+3zwNqU_9+o1fw@mail.gmail.com>
 <20150329210757.GA64665@FreeBSD.org>
Date: Sun, 29 Mar 2015 14:15:43 -0700
X-Google-Sender-Auth: 8_pQOhRozONIOuNR0Ae5RmozCcM
Message-ID: <CAJ-VmomQzEXV4KtokK7jBgqCHEwExvYxhHJBar1uY2=yB1BjAg@mail.gmail.com>
Subject: Re: svn commit: r280759 - head/sys/netinet
From: Adrian Chadd <adrian@freebsd.org>
To: Gleb Smirnoff <glebius@freebsd.org>
Content-Type: text/plain; charset=UTF-8
Cc: Hans Petter Selasky <hps@selasky.org>,
 "svn-src-head@freebsd.org" <svn-src-head@freebsd.org>,
 "svn-src-all@freebsd.org" <svn-src-all@freebsd.org>,
 "src-committers@freebsd.org" <src-committers@freebsd.org>,
 Fabien Thomas <fabient@freebsd.org>
X-BeenThere: svn-src-all@freebsd.org
X-Mailman-Version: 2.1.18-1
Precedence: list
List-Id: "SVN commit messages for the entire src tree \(except for &quot;
 user&quot; and &quot; projects&quot; \)" <svn-src-all.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/options/svn-src-all>,
 <mailto:svn-src-all-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/svn-src-all/>
List-Post: <mailto:svn-src-all@freebsd.org>
List-Help: <mailto:svn-src-all-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/svn-src-all>,
 <mailto:svn-src-all-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Sun, 29 Mar 2015 21:15:44 -0000

> To illustrate the probability of 1 instruction race, I would suggest to
> look at PCPU_ADD() implementation for all arches except amd64/i386 and
> find out that it is prone to this race. Hitting the race in PCPU_ADD()
> will usually lead to mangling vm_meter statistics. Did we ever observe
> this in practice? No.

I dunno. Has anyone actually looked at that? :)

On a busy system you may find those small race windows exist enough to
be annoying. Case in point - the recent callout code race. The race
between "read" "modify" "write" was tiny, but enough to break things.


-adrian