From owner-svn-src-all@freebsd.org  Tue Aug 16 12:54:18 2016
Return-Path: <owner-svn-src-all@freebsd.org>
Delivered-To: svn-src-all@mailman.ysv.freebsd.org
Received: from mx1.freebsd.org (mx1.freebsd.org
 [IPv6:2001:1900:2254:206a::19:1])
 by mailman.ysv.freebsd.org (Postfix) with ESMTP id C64C8BBB951;
 Tue, 16 Aug 2016 12:54:18 +0000 (UTC) (envelope-from hps@selasky.org)
Received: from mail.turbocat.net (mail.turbocat.net
 [IPv6:2a01:4f8:d16:4514::2])
 (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits))
 (Client did not present a certificate)
 by mx1.freebsd.org (Postfix) with ESMTPS id 916581A4C;
 Tue, 16 Aug 2016 12:54:18 +0000 (UTC) (envelope-from hps@selasky.org)
Received: from laptop015.home.selasky.org (unknown [62.141.129.119])
 (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits))
 (No client certificate requested)
 by mail.turbocat.net (Postfix) with ESMTPSA id 83A781FE022;
 Tue, 16 Aug 2016 14:54:16 +0200 (CEST)
Subject: Re: svn commit: r304218 - head/sys/netinet
To: Randall Stewart <rrs@FreeBSD.org>, src-committers@freebsd.org,
 svn-src-all@freebsd.org, svn-src-head@freebsd.org
References: <201608161240.u7GCeuWS082118@repo.freebsd.org>
From: Hans Petter Selasky <hps@selasky.org>
Message-ID: <92a3cfc1-56bc-813f-dd12-ac19c66fd716@selasky.org>
Date: Tue, 16 Aug 2016 14:58:45 +0200
User-Agent: Mozilla/5.0 (X11; FreeBSD amd64; rv:45.0) Gecko/20100101
 Thunderbird/45.0
MIME-Version: 1.0
In-Reply-To: <201608161240.u7GCeuWS082118@repo.freebsd.org>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 7bit
X-BeenThere: svn-src-all@freebsd.org
X-Mailman-Version: 2.1.22
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: <https://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: <https://lists.freebsd.org/mailman/listinfo/svn-src-all>,
 <mailto:svn-src-all-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Tue, 16 Aug 2016 12:54:18 -0000

On 08/16/16 14:40, Randall Stewart wrote:
> +int
> +tcp_inpinfo_lock_add(struct inpcb *inp)
> +{
> +	in_pcbref(inp);
> +	INP_WUNLOCK(inp);
> +	INP_INFO_RLOCK(&V_tcbinfo);
> +	INP_WLOCK(inp);
> +	if (inp->inp_flags & (INP_TIMEWAIT | INP_DROPPED)) {
> +		return(1);
> +	}
> +	return(0);
> +
> +}

Hi,

Could you add some comments describing how it is considered safe to drop 
the INP write-lock and then pick it up again?

My first impression is that because you are dropping the inp lock, 
multiple threads can enter the code in question, leaving the window open 
to races?

--HPS