Date: Mon, 5 Aug 2013 10:49:14 -0700 From: Jack Vogel <jfvogel@gmail.com> To: Luigi Rizzo <rizzo@iet.unipi.it> 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: <CAFOYbckJaZYQj2D4k41Nmjm9urue9_CDcdQ3yhRddWx0SzXE6g@mail.gmail.com> In-Reply-To: <CA%2BhQ2%2BgZTGmrBKTOAeFnNma4DQXbAy_y8NZrovpWqm_5BJTWhQ@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>
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Sigh, this ends up being ugly I'm afraid. I need some time to look at code and think about it. 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" >
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