path: root/Documentation/atomic_t.txt
diff options
authorBoqun Feng <>2020-03-26 10:40:21 +0800
committerPaul E. McKenney <>2020-06-29 12:05:18 -0700
commit4dcd4d36ddb1fa7fa7257ffe9e711608119b9785 (patch)
tree75832a38c12f4abf413b30ebfdd91fc01ecd6ed1 /Documentation/atomic_t.txt
parentefff6150209694a78c8af8c2a7557af682086220 (diff)
Documentation/litmus-tests/atomic: Add a test for atomic_set()
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. Besides currently the litmus test "atomic-set" in atomic_t.txt has a few things to be improved: 1) The CPU/Processor numbers "P1,P2" are not only inconsistent with the rest of the document, which uses "CPU0" and "CPU1", but also unacceptable by the herd tool, which requires processors start at "P0". 2) The initialization block uses a "atomic_set()", which is OK, but it's better to use ATOMIC_INIT() to make clear this is an initialization. 3) The return value of atomic_add_unless() is discarded inexplicitly, which is OK for C language, but it will be helpful to the herd tool if we use a void cast to make the discard explicit. 4) The name and the paragraph describing the test need to be more accurate and aligned with our wording in LKMM. Therefore fix these in both atomic_t.txt and the new added litmus test. Acked-by: Andrea Parri <> Acked-by: Alan Stern <> Signed-off-by: Boqun Feng <> Reviewed-by: Joel Fernandes (Google) <> Signed-off-by: Paul E. McKenney <>
Diffstat (limited to 'Documentation/atomic_t.txt')
1 files changed, 7 insertions, 7 deletions
diff --git a/Documentation/atomic_t.txt b/Documentation/atomic_t.txt
index 0ab747e0d5ac..67d1d99f8589 100644
--- a/Documentation/atomic_t.txt
+++ b/Documentation/atomic_t.txt
@@ -85,21 +85,21 @@ 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_set(v, 1);
+ atomic_t v = ATOMIC_INIT(1);
- P1(atomic_t *v)
+ P0(atomic_t *v)
- atomic_add_unless(v, 1, 0);
+ (void)atomic_add_unless(v, 1, 0);
- P2(atomic_t *v)
+ P1(atomic_t *v)
atomic_set(v, 0);