Date: Mon, 5 Aug 2013 19:58:56 +0200 From: Luigi Rizzo <rizzo@iet.unipi.it> To: Jack Vogel <jfvogel@gmail.com> Cc: Adrian Chadd <adrian@freebsd.org>, FreeBSD current mailing list <current@freebsd.org>, Bryan Venteicher <bryanv@daemoninthecloset.org>, Navdeep Parhar <np@freebsd.org>, net@freebsd.org, Giuseppe Lettieri <g.lettieri@iet.unipi.it> Subject: Re: [net] protecting interfaces from races between control and data ? Message-ID: <CA%2BhQ2%2BhAcyi=uFcOLV1YNMfDAmdhJoTtqtgpb=R_-RKSmWX9FQ@mail.gmail.com> In-Reply-To: <CAFOYbckJaZYQj2D4k41Nmjm9urue9_CDcdQ3yhRddWx0SzXE6g@mail.gmail.com> References: <20130805082307.GA35162@onelab2.iet.unipi.it> <2034715395.855.1375714772487.JavaMail.root@daemoninthecloset.org> <CAJ-VmokT6YKPR7CXsoCavEmWv3W8urZu4eBVgKWaj9iMaVJFZg@mail.gmail.com> <CA%2BhQ2%2BhuoCCweq7fjoYmH3nyhmhb5DzukEdPSMtaJEWa8Ft0JQ@mail.gmail.com> <51FFDD1E.1000206@FreeBSD.org> <CAJ-Vmo=Q9AqdBJ0%2B4AiX4%2BWreYuZx6VGGYw=MZ4XhMB1P2yMww@mail.gmail.com> <CA%2BhQ2%2BgZTGmrBKTOAeFnNma4DQXbAy_y8NZrovpWqm_5BJTWhQ@mail.gmail.com> <CAFOYbckJaZYQj2D4k41Nmjm9urue9_CDcdQ3yhRddWx0SzXE6g@mail.gmail.com>
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On Mon, Aug 5, 2013 at 7:49 PM, Jack Vogel <jfvogel@gmail.com> 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 <rizzo@iet.unipi.it> wrote: > >> On Mon, Aug 5, 2013 at 7:17 PM, Adrian Chadd <adrian@freebsd.org> 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) -----------------------------------------+-------------------------------
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