[RFC 3/3] tools/memory-model: Add litmus test for RMW + smp_mb__after_atomic()

[Boqun Feng]

We already use a litmus test in atomic_t.txt to describe atomic RMW +
smp_mb__after_atomic() is "strong acquire" (both the read and the write
part is ordered). So make it a litmus test in memory-model litmus-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.

Signed-off-by: Boqun Feng <boqun.feng@xxxxxxxxx>
---
 Documentation/atomic_t.txt                    |  6 ++--
 ...+mb__after_atomic-is-strong-acquire.litmus | 29 +++++++++++++++++++
 tools/memory-model/litmus-tests/README        |  5 ++++
 3 files changed, 37 insertions(+), 3 deletions(-)
 create mode 100644 tools/memory-model/litmus-tests/Atomic-RMW+mb__after_atomic-is-strong-acquire.litmus

diff --git a/Documentation/atomic_t.txt b/Documentation/atomic_t.txt
index ceb85ada378e..e3ad4e4cd9ed 100644
--- a/Documentation/atomic_t.txt
+++ b/Documentation/atomic_t.txt
@@ -238,14 +238,14 @@ strictly stronger than ACQUIRE. As illustrated:
   {
   }
 
-  P1(int *x, atomic_t *y)
+  P0(int *x, atomic_t *y)
   {
     r0 = READ_ONCE(*x);
     smp_rmb();
     r1 = atomic_read(y);
   }
 
-  P2(int *x, atomic_t *y)
+  P1(int *x, atomic_t *y)
   {
     atomic_inc(y);
     smp_mb__after_atomic();
@@ -260,7 +260,7 @@ This should not happen; but a hypothetical atomic_inc_acquire() --
 because it would not order the W part of the RMW against the following
 WRITE_ONCE.  Thus:
 
-  P1			P2
+  P0			P1
 
 			t = LL.acq *y (0)
 			t++;
diff --git a/tools/memory-model/litmus-tests/Atomic-RMW+mb__after_atomic-is-strong-acquire.litmus b/tools/memory-model/litmus-tests/Atomic-RMW+mb__after_atomic-is-strong-acquire.litmus
new file mode 100644
index 000000000000..e7216cf9d92a
--- /dev/null
+++ b/tools/memory-model/litmus-tests/Atomic-RMW+mb__after_atomic-is-strong-acquire.litmus
@@ -0,0 +1,29 @@
+C Atomic-RMW+mb__after_atomic-is-strong-acquire
+
+(*
+ * Result: Never
+ *
+ * Test of an atomic RMW followed by a smp_mb__after_atomic() is
+ * "strong-acquire": both the read and write part of the RMW is ordered before
+ * the subsequential memory accesses.
+ *)
+
+{
+}
+
+P0(int *x, atomic_t *y)
+{
+	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
+(r0=1 /\ r1=0)
diff --git a/tools/memory-model/litmus-tests/README b/tools/memory-model/litmus-tests/README
index 81eeacebd160..774e10058c72 100644
--- a/tools/memory-model/litmus-tests/README
+++ b/tools/memory-model/litmus-tests/README
@@ -2,6 +2,11 @@
 LITMUS TESTS
 ============
 
+Atomic-RMW+mb__after_atomic-is-strong-acquire
+	Test of an atomic RMW followed by a smp_mb__after_atomic() is
+	"strong-acquire": both the read and write part of the RMW is ordered
+	before the subsequential memory accesses.
+
 Atomic-set-observable-to-RMW.litmus
 	Test of the result of atomic_set() must be observable to atomic RMWs.
 
-- 
2.25.0