From: Andrea Parri <andrea.parri@amarulasolutions.com>
To: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>, Will Deacon <will.deacon@arm.com>,
Alan Stern <stern@rowland.harvard.edu>,
Boqun Feng <boqun.feng@gmail.com>,
Nicholas Piggin <npiggin@gmail.com>,
David Howells <dhowells@redhat.com>,
Jade Alglave <j.alglave@ucl.ac.uk>,
Luc Maranget <luc.maranget@inria.fr>,
Akira Yokosawa <akiyks@gmail.com>,
Daniel Lustig <dlustig@nvidia.com>,
Jonathan Corbet <corbet@lwn.net>,
Randy Dunlap <rdunlap@infradead.org>,
Matthew Wilcox <willy@infradead.org>
Subject: Re: [PATCH v3 2/3] locking: Clarify requirements for smp_mb__after_spinlock()
Date: Tue, 3 Jul 2018 19:07:57 +0200 [thread overview]
Message-ID: <20180703170757.GA3251@andrea> (raw)
In-Reply-To: <20180703153910.GZ3593@linux.vnet.ibm.com>
On Tue, Jul 03, 2018 at 08:39:10AM -0700, Paul E. McKenney wrote:
[...]
> > + * smp_mb__after_spinlock() provides the equivalent of a full memory barrier
> > + * between program-order earlier lock acquisitions and program-order later
>
> Not just the earlier lock acquisition, but also all program-order earlier
> memory accesses, correct?
I understand: "but also all program-order earlier memory accesses program-order
before that lock acquisition(s) ...". Yes, but:
- I considered this as implied by the above (L ->mb M2 and M1 ->po L implies
M1 ->mb M2, where M1, M2 are memory accesses and L is a lock acquisition);
- my prose abilities are limited ;-), and I was/am unable to come up with an
(to me) acceptable or readable enough way to make it explicit; some ideas?
> > + * WRITE_ONCE(X, 1); WRITE_ONCE(Y, 1);
> > + * spin_lock(S); smp_mb();
> > + * smp_mb__after_spinlock(); r1 = READ_ONCE(X);
> > + * r0 = READ_ONCE(Y);
> > + * spin_unlock(S);
>
> Should we say that this is an instance of the SB pattern? (Am OK either
> way, just asking the question.)
I don't think we *should* ;-), but I'm also OK either way.
Andrea
next prev parent reply other threads:[~2018-07-03 17:08 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-06-28 10:41 [PATCH 0/3] sched/locking/doc: Miscellaneous fixes Andrea Parri
2018-06-28 10:41 ` [PATCH 1/3] sched: Use smp_mb() in wake_woken_function() Andrea Parri
2018-06-28 10:41 ` [PATCH 2/3] locking: Clarify requirements for smp_mb__after_spinlock() Andrea Parri
2018-06-28 13:02 ` Matthew Wilcox
2018-06-28 13:10 ` Andrea Parri
2018-06-28 13:49 ` Alan Stern
2018-06-28 13:52 ` Andrea Parri
2018-06-28 15:05 ` Peter Zijlstra
2018-06-28 17:30 ` Andrea Parri
2018-07-02 12:50 ` Peter Zijlstra
2018-07-02 15:11 ` [PATCH v2 " Andrea Parri
2018-07-02 15:37 ` Peter Zijlstra
2018-07-03 8:49 ` Andrea Parri
2018-07-03 14:53 ` [PATCH v3 " Andrea Parri
2018-07-03 15:39 ` Paul E. McKenney
2018-07-03 17:07 ` Andrea Parri [this message]
2018-06-28 10:41 ` [PATCH 3/3] doc: Update wake_up() & co. memory-barrier guarantees Andrea Parri
2018-07-05 22:28 ` [PATCH 0/3] sched/locking/doc: Miscellaneous fixes Andrea Parri
2018-07-06 10:36 ` Peter Zijlstra
2018-07-06 14:43 ` Paul E. McKenney
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