From: Alan Stern <stern@rowland.harvard.edu>
To: "Paul E. McKenney" <paulmck@linux.ibm.com>
Cc: David Goldblatt <davidtgoldblatt@gmail.com>,
<mathieu.desnoyers@efficios.com>,
Florian Weimer <fweimer@redhat.com>, <triegel@redhat.com>,
<libc-alpha@sourceware.org>, <andrea.parri@amarulasolutions.com>,
<will.deacon@arm.com>, <peterz@infradead.org>,
<boqun.feng@gmail.com>, <npiggin@gmail.com>,
<dhowells@redhat.com>, <j.alglave@ucl.ac.uk>,
<luc.maranget@inria.fr>, <akiyks@gmail.com>, <dlustig@nvidia.com>,
<linux-arch@vger.kernel.org>, <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] Linux: Implement membarrier function
Date: Wed, 12 Dec 2018 17:12:18 -0500 (EST) [thread overview]
Message-ID: <Pine.LNX.4.44L0.1812121710350.1543-100000@iolanthe.rowland.org> (raw)
In-Reply-To: <20181212215245.GC4170@linux.ibm.com>
On Wed, 12 Dec 2018, Paul E. McKenney wrote:
> > > I believe that this ordering forbids the cycle:
> > >
> > > Wa=1 > membs -> [m01] -> Rc=0 -> Wc=2 -> rcu_read_unlock() ->
> > > return from synchronize_rcu() -> Ra
> > >
> > > Does this make sense, or am I missing something?
> >
> > It's hard to tell. What you have written here isn't justified by the
> > litmus test source code, since the position of m01 in P1's program
> > order is undetermined. How do you justify m01 -> Rc, for example?
>
> ... justifies Rc=0 following [m01].
>
> > Write it this way instead, using the relations defined in the
> > sys_membarrier patch for linux-kernel.cat:
> >
> > memb ->memb-gp memb ->rcu-link Rc ->memb-rscsi Rc ->rcu-link
> >
> > rcu_read_unlock ->rcu-rscsi rcu_read_lock ->rcu-link
> >
> > synchronize_rcu ->rcu-gp synchronize_rcu ->rcu-link memb
> >
> > Recall that:
> >
> > memb-gp is the identity relation on sys_membarrier events,
> >
> > rcu-link includes (po? ; fre ; po),
> >
> > memb-rscsi is the identity relation on all events,
> >
> > rcu-rscsi links unlocks to their corresponding locks, and
> >
> > rcu-gp is the identity relation on synchronize_rcu events.
> >
> > These facts justify the cycle above.
> >
> > Leaving off the final rcu-link step, the sequence matches the
> > definition of rcu-fence (the relations are memb-gp, memb-rscsi,
> > rcu-rscsi, rcu-gp with rcu-links in between). Therefore the cycle is
> > forbidden.
>
> Understood, but that would be using the model to check the model. ;-)
Well, what are you trying to accomplish? Do you want to find an
argument similar to the one I posted for the 6-CPU test to show that
this test should be forbidden?
Alan
WARNING: multiple messages have this Message-ID (diff)
From: Alan Stern <stern@rowland.harvard.edu>
To: "Paul E. McKenney" <paulmck@linux.ibm.com>
Cc: David Goldblatt <davidtgoldblatt@gmail.com>,
mathieu.desnoyers@efficios.com,
Florian Weimer <fweimer@redhat.com>,
triegel@redhat.com, libc-alpha@sourceware.org,
andrea.parri@amarulasolutions.com, will.deacon@arm.com,
peterz@infradead.org, boqun.feng@gmail.com, npiggin@gmail.com,
dhowells@redhat.com, j.alglave@ucl.ac.uk, luc.maranget@inria.fr,
akiyks@gmail.com, dlustig@nvidia.com, linux-arch@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] Linux: Implement membarrier function
Date: Wed, 12 Dec 2018 17:12:18 -0500 (EST) [thread overview]
Message-ID: <Pine.LNX.4.44L0.1812121710350.1543-100000@iolanthe.rowland.org> (raw)
In-Reply-To: <20181212215245.GC4170@linux.ibm.com>
On Wed, 12 Dec 2018, Paul E. McKenney wrote:
> > > I believe that this ordering forbids the cycle:
> > >
> > > Wa=1 > membs -> [m01] -> Rc=0 -> Wc=2 -> rcu_read_unlock() ->
> > > return from synchronize_rcu() -> Ra
> > >
> > > Does this make sense, or am I missing something?
> >
> > It's hard to tell. What you have written here isn't justified by the
> > litmus test source code, since the position of m01 in P1's program
> > order is undetermined. How do you justify m01 -> Rc, for example?
>
> ... justifies Rc=0 following [m01].
>
> > Write it this way instead, using the relations defined in the
> > sys_membarrier patch for linux-kernel.cat:
> >
> > memb ->memb-gp memb ->rcu-link Rc ->memb-rscsi Rc ->rcu-link
> >
> > rcu_read_unlock ->rcu-rscsi rcu_read_lock ->rcu-link
> >
> > synchronize_rcu ->rcu-gp synchronize_rcu ->rcu-link memb
> >
> > Recall that:
> >
> > memb-gp is the identity relation on sys_membarrier events,
> >
> > rcu-link includes (po? ; fre ; po),
> >
> > memb-rscsi is the identity relation on all events,
> >
> > rcu-rscsi links unlocks to their corresponding locks, and
> >
> > rcu-gp is the identity relation on synchronize_rcu events.
> >
> > These facts justify the cycle above.
> >
> > Leaving off the final rcu-link step, the sequence matches the
> > definition of rcu-fence (the relations are memb-gp, memb-rscsi,
> > rcu-rscsi, rcu-gp with rcu-links in between). Therefore the cycle is
> > forbidden.
>
> Understood, but that would be using the model to check the model. ;-)
Well, what are you trying to accomplish? Do you want to find an
argument similar to the one I posted for the 6-CPU test to show that
this test should be forbidden?
Alan
next prev parent reply other threads:[~2018-12-12 22:12 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <8736rldyzm.fsf@oldenburg.str.redhat.com>
[not found] ` <1543444466.5493.220.camel@redhat.com>
[not found] ` <87y39c2dsg.fsf@oldenburg.str.redhat.com>
[not found] ` <1689938209.14804.1543502662882.JavaMail.zimbra@efficios.com>
[not found] ` <20181129150433.GH4170@linux.ibm.com>
[not found] ` <CAHD6eXcvx1bskbp-X+vuMYoMQiCLOt0PiCZ5FT1yFsda9Ud-yA@mail.gmail.com>
2018-12-06 21:54 ` [PATCH] Linux: Implement membarrier function Paul E. McKenney
2018-12-10 16:22 ` Alan Stern
2018-12-10 16:22 ` Alan Stern
2018-12-10 18:25 ` Paul E. McKenney
2018-12-11 16:21 ` Alan Stern
2018-12-11 16:21 ` Alan Stern
2018-12-11 19:08 ` Paul E. McKenney
2018-12-11 20:09 ` Alan Stern
2018-12-11 20:09 ` Alan Stern
2018-12-11 21:22 ` Paul E. McKenney
2018-12-12 17:07 ` Paul E. McKenney
2018-12-12 18:04 ` Alan Stern
2018-12-12 18:04 ` Alan Stern
2018-12-12 19:42 ` Paul E. McKenney
2018-12-12 21:32 ` Alan Stern
2018-12-12 21:32 ` Alan Stern
2018-12-12 21:52 ` Paul E. McKenney
2018-12-12 22:12 ` Alan Stern [this message]
2018-12-12 22:12 ` Alan Stern
2018-12-12 22:49 ` Paul E. McKenney
2018-12-13 15:49 ` Alan Stern
2018-12-13 15:49 ` Alan Stern
2018-12-14 0:20 ` Paul E. McKenney
2018-12-14 2:26 ` Alan Stern
2018-12-14 2:26 ` Alan Stern
2018-12-14 5:20 ` Paul E. McKenney
2018-12-14 15:31 ` Alan Stern
2018-12-14 15:31 ` Alan Stern
2018-12-14 18:43 ` Paul E. McKenney
2018-12-14 21:39 ` Alan Stern
2018-12-14 21:39 ` Alan Stern
2018-12-16 18:51 ` Paul E. McKenney
2018-12-17 16:02 ` Alan Stern
2018-12-17 16:02 ` Alan Stern
2018-12-17 18:32 ` Paul E. McKenney
2018-12-12 22:19 ` Paul E. McKenney
2018-12-11 6:42 ` David Goldblatt
2018-12-11 14:49 ` Paul E. McKenney
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