From: Joel Fernandes <joel@joelfernandes.org>
To: Boqun Feng <boqun.feng@gmail.com>
Cc: linux-kernel@vger.kernel.org,
Alan Stern <stern@rowland.harvard.edu>,
Andrea Parri <parri.andrea@gmail.com>,
Will Deacon <will@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Nicholas Piggin <npiggin@gmail.com>,
David Howells <dhowells@redhat.com>,
Jade Alglave <j.alglave@ucl.ac.uk>,
Luc Maranget <luc.maranget@inria.fr>,
"Paul E. McKenney" <paulmck@kernel.org>,
Akira Yokosawa <akiyks@gmail.com>,
Daniel Lustig <dlustig@nvidia.com>,
Jonathan Corbet <corbet@lwn.net>,
Mauro Carvalho Chehab <mchehab+samsung@kernel.org>,
"David S. Miller" <davem@davemloft.net>,
Rob Herring <robh@kernel.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Jonathan Cameron <Jonathan.Cameron@huawei.com>,
linux-arch@vger.kernel.org, linux-doc@vger.kernel.org
Subject: Re: [PATCH v4 0/4] Documentation/litmus-tests: Add litmus tests for atomic APIs
Date: Wed, 1 Apr 2020 23:58:16 -0400 [thread overview]
Message-ID: <20200402035816.GA46686@google.com> (raw)
In-Reply-To: <20200331014037.GB59159@debian-boqun.qqnc3lrjykvubdpftowmye0fmh.lx.internal.cloudapp.net>
On Tue, Mar 31, 2020 at 09:40:37AM +0800, Boqun Feng wrote:
> On Fri, Mar 27, 2020 at 06:18:43PM -0400, Joel Fernandes wrote:
> > On Thu, Mar 26, 2020 at 10:40:18AM +0800, Boqun Feng wrote:
> > > A recent discussion raises up the requirement for having test cases for
> > > atomic APIs:
> > >
> > > https://lore.kernel.org/lkml/20200213085849.GL14897@hirez.programming.kicks-ass.net/
> > >
> > > , and since we already have a way to generate a test module from a
> > > litmus test with klitmus[1]. It makes sense that we add more litmus
> > > tests for atomic APIs. And based on the previous discussion, I create a
> > > new directory Documentation/atomic-tests and put these litmus tests
> > > here.
> > >
> > > This patchset starts the work by adding the litmus tests which are
> > > already used in atomic_t.txt, and also improve the atomic_t.txt to make
> > > it consistent with the litmus tests.
> > >
> > > Previous version:
> > > v1: https://lore.kernel.org/linux-doc/20200214040132.91934-1-boqun.feng@gmail.com/
> > > v2: https://lore.kernel.org/lkml/20200219062627.104736-1-boqun.feng@gmail.com/
> > > v3: https://lore.kernel.org/linux-doc/20200227004049.6853-1-boqun.feng@gmail.com/
> >
> > For full series:
> >
> > Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
> >
> > One question I had was in the existing atomic_set() documentation, it talks
> > about atomic_add_unless() implementation based on locking could have issues.
> > It says the way to fix such cases is:
> >
> > Quote:
> > the typical solution is to then implement atomic_set{}() with
> > atomic_xchg().
> >
> > I didn't get how using atomic_xchg() fixes it. Is the assumption there that
> > atomic_xchg() would be implemented using locking to avoid atomic_set() having
>
> Right, I think that's the intent of the sentence.
>
> > issues? If so, we could clarify that in the document.
> >
>
> Patches are welcome ;-)
---8<-----------------------
Like this? I'll add it to my tree and send it to Paul during my next
series, unless you disagree ;-)
Subject: [PATCH] doc: atomic_t: Document better about the locking within
atomic_xchg()
It is not fully clear how the atomic_set() would not cause an issue with
preservation of the atomicity of RMW in this example. Make it clear that
locking within atomic_xchg() would save the day.
Suggested-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
---
Documentation/atomic_t.txt | 2 ++
1 file changed, 2 insertions(+)
diff --git a/Documentation/atomic_t.txt b/Documentation/atomic_t.txt
index 0f1fdedf36bbb..1d9c307c73a7c 100644
--- a/Documentation/atomic_t.txt
+++ b/Documentation/atomic_t.txt
@@ -129,6 +129,8 @@ with a lock:
unlock();
the typical solution is to then implement atomic_set{}() with atomic_xchg().
+The locking within the atomic_xchg() in CPU1 would ensure that the value read
+in CPU0 would not be overwritten.
RMW ops:
--
2.26.0.292.g33ef6b2f38-goog
next prev parent reply other threads:[~2020-04-02 3:58 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-26 2:40 [PATCH v4 0/4] Documentation/litmus-tests: Add litmus tests for atomic APIs Boqun Feng
2020-03-26 2:40 ` [PATCH v4 1/4] tools/memory-model: Add an exception for limitations on _unless() family Boqun Feng
2020-03-26 2:40 ` [PATCH v4 2/4] Documentation/litmus-tests: Introduce atomic directory Boqun Feng
2020-03-26 2:40 ` [PATCH v4 3/4] Documentation/litmus-tests/atomic: Add a test for atomic_set() Boqun Feng
2020-03-26 14:23 ` Alan Stern
2020-03-26 2:40 ` [PATCH v4 4/4] Documentation/litmus-tests/atomic: Add a test for smp_mb__after_atomic() Boqun Feng
2020-03-27 22:18 ` [PATCH v4 0/4] Documentation/litmus-tests: Add litmus tests for atomic APIs Joel Fernandes
2020-03-31 1:40 ` Boqun Feng
2020-04-02 3:58 ` Joel Fernandes [this message]
2020-04-02 8:03 ` Boqun Feng
2020-04-04 19:57 ` Joel Fernandes
2020-04-01 16:34 ` Paul E. McKenney
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