From owner-freebsd-current@FreeBSD.ORG Mon Aug 5 17:58:59 2013 Return-Path: Delivered-To: current@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) (using TLSv1 with cipher ADH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTP id C27597D; Mon, 5 Aug 2013 17:58:59 +0000 (UTC) (envelope-from rizzo.unipi@gmail.com) Received: from mail-la0-x229.google.com (mail-la0-x229.google.com [IPv6:2a00:1450:4010:c03::229]) (using TLSv1 with cipher ECDHE-RSA-RC4-SHA (128/128 bits)) (No client certificate requested) by mx1.freebsd.org (Postfix) with ESMTPS id 92C162C17; Mon, 5 Aug 2013 17:58:58 +0000 (UTC) Received: by mail-la0-f41.google.com with SMTP id ec20so2316316lab.0 for ; Mon, 05 Aug 2013 10:58:56 -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 :x-google-sender-auth:message-id:subject:from:to:cc:content-type; bh=6ZtvieGuGGhAoaS120XU/yBY9J5erKykOaKC1g2RHZM=; b=UDqfQxf4mqMb/UO47n6zUdZVEG+2QScx44XHXDKrGBij62yi6VgwfstSwP/4mRjeuP C3i1p87rUezNa7tErAFgfUfxtWM0zMzWIF4HLrgAZDYfYzvMxQ/1y3rwFKsabmX94ICk kdEOYdrztO04jq/AsqhYvRB4X2RlpLRvc629P/97Eh3gCL9o6vIRU7XqY+ObccFghCuh Ybgbw+wlWKU66CxpjwycKgZDFDF2gE+J+yMa6Uf8lUBcRZ1OTAp/J6CpfdDBfW4Gw1xr lk5eNM12nASMeUTxeAk0bbnUclap+UbbBppZnQPM7pRf0MA/YcO+auRNOOXIZ2rSKBv5 S9Xw== MIME-Version: 1.0 X-Received: by 10.152.36.198 with SMTP id s6mr5661194laj.67.1375725536550; Mon, 05 Aug 2013 10:58:56 -0700 (PDT) Sender: rizzo.unipi@gmail.com Received: by 10.114.200.165 with HTTP; Mon, 5 Aug 2013 10:58:56 -0700 (PDT) In-Reply-To: References: <20130805082307.GA35162@onelab2.iet.unipi.it> <2034715395.855.1375714772487.JavaMail.root@daemoninthecloset.org> <51FFDD1E.1000206@FreeBSD.org> Date: Mon, 5 Aug 2013 19:58:56 +0200 X-Google-Sender-Auth: -7AMBJyuIckaxEZBCuXlzZJHyq0 Message-ID: Subject: Re: [net] protecting interfaces from races between control and data ? From: Luigi Rizzo To: Jack Vogel Content-Type: text/plain; charset=ISO-8859-1 X-Content-Filtered-By: Mailman/MimeDel 2.1.14 Cc: Adrian Chadd , FreeBSD current mailing list , Bryan Venteicher , Navdeep Parhar , net@freebsd.org, Giuseppe Lettieri X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 05 Aug 2013 17:58:59 -0000 On Mon, Aug 5, 2013 at 7:49 PM, Jack Vogel wrote: > Sigh, this ends up being ugly I'm afraid. I need some time to look at code > and think about it. > > actually the intel drivers seem in decent shape, especially if we reuse IFF_DRV_RUNNING as the reset flag and the core+queue lock in the control path. cheers luigi > Jack > > > > On Mon, Aug 5, 2013 at 10:36 AM, Luigi Rizzo wrote: > >> On Mon, Aug 5, 2013 at 7:17 PM, Adrian Chadd wrote: >> >> > I'm travelling back to San Jose today; poke me tomorrow and I'll brain >> > dump what I did in ath(4) and the lessons learnt. >> > >> > The TL;DR version - you don't want to grab an extra lock in the >> > read/write paths as that slows things down. Reuse the same per-queue >> > TX/RX lock and have: >> > >> > * a reset flag that is set when something is resetting; that says to >> > the queue "don't bother processing anything, just dive out"; >> > * 'i am doing Tx / Rx' flags per queue that is set at the start of >> > TX/RX servicing and finishes at the end; that way the reset code knows >> > if there's something pending; >> > * have the reset path grab each lock, set the 'reset' flag on each, >> > then walk each queue again and make sure they're all marked as 'not >> > doing TX/RX'. At that point the reset can occur, then the flag cna be >> > cleared, then TX/RX can resume. >> > >> >> so this is slightly different from what Bryan suggested (and you endorsed) >> before, as in that case there was a single 'reset' flag IFF_DRV_RUNNING >> protected by the 'core' lock, then a nested round on all tx and rx locks >> to make sure that all customers have seen it. >> In both cases the tx and rx paths only need the per-queue lock. >> >> As i see it, having a per-queue reset flag removes the need for nesting >> core + queue locks, but since this is only in the control path perhaps >> it is not a big deal (and is better to have a single place to look at to >> tell whether or not we should bail out). >> >> cheers >> luigi >> >> _______________________________________________ >> freebsd-net@freebsd.org mailing list >> http://lists.freebsd.org/mailman/listinfo/freebsd-net >> To unsubscribe, send any mail to "freebsd-net-unsubscribe@freebsd.org" >> > > -- -----------------------------------------+------------------------------- Prof. Luigi RIZZO, rizzo@iet.unipi.it . Dip. di Ing. dell'Informazione http://www.iet.unipi.it/~luigi/ . Universita` di Pisa TEL +39-050-2211611 . via Diotisalvi 2 Mobile +39-338-6809875 . 56122 PISA (Italy) -----------------------------------------+-------------------------------