From 4dcd4d36ddb1fa7fa7257ffe9e711608119b9785 Mon Sep 17 00:00:00 2001 From: Boqun Feng Date: Thu, 26 Mar 2020 10:40:21 +0800 Subject: [PATCH] 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 --- Documentation/atomic_t.txt | 18 +++++++------- ...c-RMW-ops-are-atomic-WRT-atomic_set.litmus | 24 +++++++++++++++++++ Documentation/litmus-tests/atomic/README | 7 ++++++ 3 files changed, 40 insertions(+), 9 deletions(-) create mode 100644 Documentation/litmus-tests/atomic/Atomic-RMW-ops-are-atomic-WRT-atomic_set.litmus 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); + } + + P0(atomic_t *v) + { + (void)atomic_add_unless(v, 1, 0); } P1(atomic_t *v) - { - atomic_add_unless(v, 1, 0); - } - - P2(atomic_t *v) { atomic_set(v, 0); } diff --git a/Documentation/litmus-tests/atomic/Atomic-RMW-ops-are-atomic-WRT-atomic_set.litmus b/Documentation/litmus-tests/atomic/Atomic-RMW-ops-are-atomic-WRT-atomic_set.litmus new file mode 100644 index 000000000000..49385314d911 --- /dev/null +++ b/Documentation/litmus-tests/atomic/Atomic-RMW-ops-are-atomic-WRT-atomic_set.litmus @@ -0,0 +1,24 @@ +C Atomic-RMW-ops-are-atomic-WRT-atomic_set + +(* + * 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/litmus-tests/atomic/README b/Documentation/litmus-tests/atomic/README index ae61201a4271..a1b72410b539 100644 --- a/Documentation/litmus-tests/atomic/README +++ b/Documentation/litmus-tests/atomic/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.