Documentation/litmus-tests/atomic: Add a test for smp_mb__after_atomic()

We already use a litmus test in atomic_t.txt to describe atomic RMW +
smp_mb__after_atomic() is stronger than acquire (both the read and the
write parts are ordered). So make it a litmus test in atomic-tests
directory, so that people can access the litmus easily.

Additionally, change the processor numbers "P1, P2" to "P0, P1" in
atomic_t.txt for the consistency with the processor numbers in the
litmus test, which herd can handle.

Acked-by: Alan Stern <stern@rowland.harvard.edu>
Acked-by: Andrea Parri <parri.andrea@gmail.com>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

2 files changed, 37 insertions, 0 deletions

diff --git a/Documentation/litmus-tests/atomic/Atomic-RMW+mb__after_atomic-is-stronger-than-acquire.litmus b/Documentation/litmus-tests/atomic/Atomic-RMW+mb__after_atomic-is-stronger-than-acquire.litmus
new file mode 100644
index 00000000000000..9a8e31a44b2849
--- /dev/null
+++ b/Documentation/litmus-tests/atomic/Atomic-RMW+mb__after_atomic-is-stronger-than-acquire.litmus
@@ -0,0 +1,32 @@
+C Atomic-RMW+mb__after_atomic-is-stronger-than-acquire
+
+(*
+ * Result: Never
+ *
+ * Test that an atomic RMW followed by a smp_mb__after_atomic() is
+ * stronger than a normal acquire: both the read and write parts of
+ * the RMW are ordered before the subsequential memory accesses.
+ *)
+
+{
+}
+
+P0(int *x, atomic_t *y)
+{
+	int r0;
+	int r1;
+
+	r0 = READ_ONCE(*x);
+	smp_rmb();
+	r1 = atomic_read(y);
+}
+
+P1(int *x, atomic_t *y)
+{
+	atomic_inc(y);
+	smp_mb__after_atomic();
+	WRITE_ONCE(*x, 1);
+}
+
+exists
+(0:r0=1 /\ 0:r1=0)
diff --git a/Documentation/litmus-tests/atomic/README b/Documentation/litmus-tests/atomic/README
index a1b72410b5394a..714cf93816ea7e 100644
--- a/Documentation/litmus-tests/atomic/README
+++ b/Documentation/litmus-tests/atomic/README
@@ -7,5 +7,10 @@ tools/memory-model/README.
 LITMUS TESTS
 ============
 
+Atomic-RMW+mb__after_atomic-is-stronger-than-acquire
+	Test that an atomic RMW followed by a smp_mb__after_atomic() is
+	stronger than a normal acquire: both the read and write parts of
+	the RMW are ordered before the subsequential memory accesses.
+
 Atomic-RMW-ops-are-atomic-WRT-atomic_set.litmus
 	Test that atomic_set() cannot break the atomicity of atomic RMWs.