This adds an example for the important RCU grace period guarantee, which
shows an RCU reader can never span a grace period.
Signed-off-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
---
.../litmus-tests/RCU+sync+read.litmus | 37 +++++++++++++++++++
1 file changed, 37 insertions(+)
create mode 100644 tools/memory-model/litmus-tests/RCU+sync+read.litmus
diff --git a/tools/memory-model/litmus-tests/RCU+sync+read.litmus b/tools/memory-model/litmus-tests/RCU+sync+read.litmus
new file mode 100644
index 0000000000000..73557772e2a32
--- /dev/null
+++ b/tools/memory-model/litmus-tests/RCU+sync+read.litmus
@@ -0,0 +1,37 @@
+C RCU+sync+read
+
+(*
+ * Result: Never
+ *
+ * This litmus test demonstrates that after a grace period, an RCU updater always
+ * sees all stores done in prior RCU read-side critical sections. Such
+ * read-side critical sections would have ended before the grace period ended.
+ *
+ * This guarantee also implies, an RCU reader can never span a grace period and
+ * is an important RCU grace period memory ordering guarantee.
+ *)
+
+{
+x = 0;
+y = 0;
+}
+
+P0(int *x, int *y)
+{
+ rcu_read_lock();
+ WRITE_ONCE(*x, 1);
+ WRITE_ONCE(*y, 1);
+ rcu_read_unlock();
+}
+
+P1(int *x, int *y)
+{
+ int r0;
+ int r1;
+
+ r0 = READ_ONCE(*x);
+ synchronize_rcu();
+ r1 = READ_ONCE(*y);
+}
+
+exists (1:r0=1 /\ 1:r1=0)
--
2.25.1.696.g5e7596f4ac-goog
