From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Boqun Feng <boqun.feng@gmail.com>
Cc: Will Deacon <will.deacon@arm.com>,
Peter Zijlstra <peterz@infradead.org>,
linux-kernel@vger.kernel.org, Ingo Molnar <mingo@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Randy Dunlap <rdunlap@infradead.org>
Subject: Re: [RFC][PATCH v3]: documentation,atomic: Add new documents
Date: Thu, 3 Aug 2017 07:55:14 -0700 [thread overview]
Message-ID: <20170803145514.GS3730@linux.vnet.ibm.com> (raw)
In-Reply-To: <20170803135718.wx2lwlm5aglvhyh5@tardis>
On Thu, Aug 03, 2017 at 10:05:16PM +0800, Boqun Feng wrote:
> Hi Will,
>
> On Wed, Aug 02, 2017 at 10:45:32AM +0100, Will Deacon wrote:
> [...]
> >
> > It's worth noting that we don't have the problem with any value-returning
> > atomics, so all flavours of xchg in this test would be forbidden on arm64
> > too.
> >
> > > C C-WillDeacon-MP+o-r+ai-rmb-o.litmus
> > >
> > > (*
> > > * Expected result: Never.
> > > *
> > > * Desired litmus test, with atomic_inc() emulated by xchg_relaxed():
> > > *
> > > * WRITE_ONCE(x, 1); atomic_inc(&y);
> > > * r0 = xchg_release(&y, 5); smp_rmb();
> > > * r1 = READ_ONCE(x);
> > > *
> > > *
> > > * WARN_ON(r0 == 0 && r1 == 0);
> > > *)
> > >
> > > {
> > > }
> > >
> > > P0(int *x, int *y)
> > > {
> > > WRITE_ONCE(*x, 1);
> > > r0 = xchg_release(y, 5);
> > > }
> > >
> > > P1(int *x, int *y)
> > > {
> > > r2 = xchg_relaxed(y, 1);
> > > smp_rmb();
> > > r1 = READ_ONCE(*x);
> > > }
> > >
> > > exists
> > > (0:r0=0 /\ 1:r1=0)
> > >
>
> How about a litmus test like this?
>
> C C-AMO-global-transitivity.litmus
>
> {
> }
>
> P0(int *x, int *y)
> {
> WRITE_ONCE(*x, 1);
> r0 = xchg_release(y, 5);
> }
>
> P1(int *y, int *z)
> {
> atomic_inc(y);
> smp_mb();
I am going to guess that the smp_mb() enforces the needed ordering,
but Will will let me know. ;-)
Thanx, Paul
> r1 = READ_ONCE(*z);
> }
>
> P2(int *x, int *z)
> {
> WRITE_ONCE(*z, 1);
> smp_mb();
> r2 = READ_ONCE(*x);
> }
>
> exists
> (0:r0=0 /\ 1:r1=0 /\ 2:r2=0 )
>
> Should we forbid the outcome in the exists-clause? I ask because I want
> to know whether we can just treat atomic_inc() as a store, because if I
> replace atomic_inc() with a WRITE(*y, 6), IIUC, the current model says
> this could happen.
>
> Thoughts?
>
> Regards,
> Boqun
next prev parent reply other threads:[~2017-08-03 14:55 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-06-09 9:24 [RFC][PATCH]: documentation,atomic: Add a new atomic_t document Peter Zijlstra
2017-06-09 11:05 ` [RFC][PATCH] atomic: Fix atomic_set_release() for 'funny' architectures Peter Zijlstra
2017-06-09 11:13 ` Peter Zijlstra
2017-06-09 17:28 ` Vineet Gupta
2017-06-09 18:49 ` Peter Zijlstra
2017-06-09 18:58 ` James Bottomley
2017-06-09 14:03 ` Chris Metcalf
2017-08-10 12:10 ` [tip:locking/core] locking/atomic: " tip-bot for Peter Zijlstra
2017-06-09 15:44 ` [RFC][PATCH]: documentation,atomic: Add a new atomic_t document Will Deacon
2017-06-09 19:36 ` Peter Zijlstra
2017-06-11 13:56 ` Boqun Feng
2017-06-12 14:49 ` Peter Zijlstra
2017-06-13 6:39 ` Boqun Feng
2017-06-14 12:33 ` Will Deacon
2017-07-12 12:53 ` Boqun Feng
2017-07-12 13:08 ` Peter Zijlstra
2017-07-12 19:13 ` Paul E. McKenney
2017-07-26 11:53 ` [RFC][PATCH v3]: documentation,atomic: Add new documents Peter Zijlstra
2017-07-26 12:47 ` Boqun Feng
2017-07-31 9:05 ` Peter Zijlstra
2017-07-31 11:04 ` Boqun Feng
2017-07-31 17:43 ` Paul E. McKenney
2017-08-01 2:14 ` Boqun Feng
2017-08-01 9:01 ` Peter Zijlstra
2017-08-01 10:19 ` Will Deacon
2017-08-01 11:47 ` Peter Zijlstra
2017-08-01 12:17 ` Will Deacon
2017-08-01 12:52 ` Peter Zijlstra
2017-08-01 16:14 ` Paul E. McKenney
2017-08-01 16:42 ` Peter Zijlstra
2017-08-01 16:53 ` Will Deacon
2017-08-01 22:18 ` Paul E. McKenney
2017-08-02 8:46 ` Will Deacon
2017-08-01 18:37 ` Paul E. McKenney
2017-08-02 9:45 ` Will Deacon
2017-08-02 16:17 ` Paul E. McKenney
2017-08-03 14:05 ` Boqun Feng
2017-08-03 14:55 ` Paul E. McKenney [this message]
2017-08-03 16:12 ` Will Deacon
2017-08-03 16:58 ` Paul E. McKenney
2017-08-01 13:35 ` Paul E. McKenney
2017-07-26 16:28 ` Randy Dunlap
2017-06-09 18:15 ` [RFC][PATCH]: documentation,atomic: Add a new atomic_t document Randy Dunlap
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