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Subject[PATCH v3 4/5] Documentation/locking/atomic: Add a litmus test for atomic_set()
Date
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..67d1d99f8589 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 must not 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
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