Date: Tue, 18 Aug 2015 05:45:15 -0700
From: Darren Hart <dvhart@infradead.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>,
        Torvald Riegel <triegel@redhat.com>,
        "Carlos O'Donell" <carlos@redhat.com>, Ingo Molnar <mingo@elte.hu>,
        Jakub Jelinek <jakub@redhat.com>,
        linux-man <linux-man@vger.kernel.org>,
        lkml <linux-kernel@vger.kernel.org>,
        Davidlohr Bueso <dave@stgolabs.net>, Arnd Bergmann <arnd@arndb.de>,
        Steven Rostedt <rostedt@goodmis.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Linux API <linux-api@vger.kernel.org>,
        Roland McGrath <roland@hack.frob.com>,
        Anton Blanchard <anton@samba.org>, Eric Dumazet <edumazet@google.com>,
        bill o gallmeister <bgallmeister@gmail.com>,
        Jan Kiszka <jan.kiszka@siemens.com>, Daniel Wagner <wagi@monom.org>,
        Rich Felker <dalias@libc.org>, Andy Lutomirski <luto@amacapital.net>,
        bert hubert <bert.hubert@netherlabs.nl>,
        Rusty Russell <rusty@rustcorp.com.au>,
        Heinrich Schuchardt <xypron.glpk@gmx.de>
Subject: Re: Next round: revised futex(2) man page for review
Message-ID: <20150818124515.GA13787@vmdeb7>
References: <55B61EF3.7080302@gmail.com>
 <20150805222140.GA74817@vmdeb7>
 <alpine.DEB.2.11.1508200031220.3873@nanos>
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On Thu, Aug 20, 2015 at 12:40:46AM +0200, Thomas Gleixner wrote:
> On Wed, 5 Aug 2015, Darren Hart wrote:
> > On Mon, Jul 27, 2015 at 02:07:15PM +0200, Michael Kerrisk (man-pages) wrote:
> > > .\" FIXME XXX ===== Start of adapted Hart/Guniguntala text =====
> > > .\"       The following text is drawn from the Hart/Guniguntala paper
> > > .\"       (listed in SEE ALSO), but I have reworded some pieces
> > > .\"       significantly. Please check it.
> > > 
> > >        The PI futex operations described below  differ  from  the  other
> > >        futex  operations  in  that  they impose policy on the use of the
> > >        value of the futex word:
> > > 
> > >        *  If the lock is not acquired, the futex word's value  shall  be
> > >           0.
> > > 
> > >        *  If  the  lock is acquired, the futex word's value shall be the
> > >           thread ID (TID; see gettid(2)) of the owning thread.
> > > 
> > >        *  If the lock is owned and there are threads contending for  the
> > >           lock,  then  the  FUTEX_WAITERS  bit shall be set in the futex
> > >           word's value; in other words, this value is:
> > > 
> > >               FUTEX_WAITERS | TID
> > > 
> > > 
> > >        Note that a PI futex word never just has the value FUTEX_WAITERS,
> > >        which is a permissible state for non-PI futexes.
> > 
> > The second clause is inappropriate. I don't know if that was yours or
> > mine, but non-PI futexes do not have a kernel defined value policy, so
> > ==FUTEX_WAITERS cannot be a "permissible state" as any value is
> > permissible for non-PI futexes, and none have a kernel defined state.
> 
> Depends. If the regular futex is configured as robust, then we have a
> kernel defined value policy as well.

Indeed, thanks for catching that.

-- 
Darren Hart
Intel Open Source Technology Center
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