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From:   Boqun Feng <boqun.feng@gmail.com>
To:     linux-kernel@vger.kernel.org
Cc:     Alan Stern <stern@rowland.harvard.edu>,
        Andrea Parri <parri.andrea@gmail.com>,
        Will Deacon <will@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        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>,
        "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: [RFC v2 3/4] Documentation/locking/atomic: Add a litmus test for atomic_set()
Date:   Wed, 19 Feb 2020 14:26:26 +0800
Message-Id: <20200219062627.104736-4-boqun.feng@gmail.com>
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We already use a litmus test in atomic_t.txt to describe the behavior of
an atomic_set() with the an atomic RMW, so add it into atomic-tests
directory to make it easily accessible for anyone who cares about the
semantics of our atomic APIs.

Additionally, change the sentences describing the test in atomic_t.txt
with better wording.

Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
---
 ...c-RMW-ops-are-atomic-WRT-atomic_set.litmus | 24 +++++++++++++++++++
 Documentation/atomic-tests/README             |  7 ++++++
 Documentation/atomic_t.txt                    |  6 ++---
 3 files changed, 34 insertions(+), 3 deletions(-)
 create mode 100644 Documentation/atomic-tests/Atomic-RMW-ops-are-atomic-WRT-atomic_set.litmus

diff --git a/Documentation/atomic-tests/Atomic-RMW-ops-are-atomic-WRT-atomic_set.litmus b/Documentation/atomic-tests/Atomic-RMW-ops-are-atomic-WRT-atomic_set.litmus
new file mode 100644
index 000000000000..5dd7f04e504a
--- /dev/null
+++ b/Documentation/atomic-tests/Atomic-RMW-ops-are-atomic-WRT-atomic_set.litmus
@@ -0,0 +1,24 @@
+C Atomic-set-observable-to-RMW
+
+(*
+ * Result: Never
+ *
+ * Test that atomic_set() cannot break the atomicity of atomic RMWs.
+ *)
+
+{
+	atomic_t v = ATOMIC_INIT(1);
+}
+
+P0(atomic_t *v)
+{
+	(void)atomic_add_unless(v,1,0);
+}
+
+P1(atomic_t *v)
+{
+	atomic_set(v, 0);
+}
+
+exists
+(v=2)
diff --git a/Documentation/atomic-tests/README b/Documentation/atomic-tests/README
index ae61201a4271..a1b72410b539 100644
--- a/Documentation/atomic-tests/README
+++ b/Documentation/atomic-tests/README
@@ -2,3 +2,10 @@ This directory contains litmus tests that are typical to describe the semantics
 of our atomic APIs. For more information about how to "run" a litmus test or
 how to generate a kernel test module based on a litmus test, please see
 tools/memory-model/README.
+
+============
+LITMUS TESTS
+============
+
+Atomic-RMW-ops-are-atomic-WRT-atomic_set.litmus
+	Test that atomic_set() cannot break the atomicity of atomic RMWs.
diff --git a/Documentation/atomic_t.txt b/Documentation/atomic_t.txt
index ceb85ada378e..d30cb3d87375 100644
--- a/Documentation/atomic_t.txt
+++ b/Documentation/atomic_t.txt
@@ -85,10 +85,10 @@ smp_store_release() respectively. Therefore, if you find yourself only using
 the Non-RMW operations of atomic_t, you do not in fact need atomic_t at all
 and are doing it wrong.
 
-A subtle detail of atomic_set{}() is that it should be observable to the RMW
-ops. That is:
+A note for the implementation of atomic_set{}() is that it cannot break the
+atomicity of the RMW ops. That is:
 
-  C atomic-set
+  C Atomic-RMW-ops-are-atomic-WRT-atomic_set
 
   {
     atomic_t v = ATOMIC_INIT(1);
-- 
2.25.0