[PATCH tip/core/rcu 04/14] Documentation: LKMM: Add litmus test for RCU GP guarantee where reader stores

paulmck
2020-06-23T00:52:46Z

From: "Joel Fernandes (Google)" <joel@joelfernandes.org>

This adds an example for the important RCU grace period guarantee, which
shows an RCU reader can never span a grace period.

Acked-by: Andrea Parri <parri.andrea@gmail.com>
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
Documentation/litmus-tests/README | 11 +++++++
.../litmus-tests/rcu/RCU+sync+read.litmus | 37 ++++++++++++++++++++++
2 files changed, 48 insertions(+)
create mode 100644 Documentation/litmus-tests/README
create mode 100644 Documentation/litmus-tests/rcu/RCU+sync+read.litmus

diff --git a/Documentation/litmus-tests/README b/Documentation/litmus-tests/README
new file mode 100644
index 0000000..c4307ea
--- /dev/null
+++ b/Documentation/litmus-tests/README
@@ -0,0 +1,11 @@
+============
+LITMUS TESTS
+============
+
+RCU (/rcu directory)
+--------------------
+
+RCU+sync+read.litmus
+RCU+sync+free.litmus
+ Both the above litmus tests demonstrate the RCU grace period guarantee
+ that an RCU read-side critical section can never span a grace period.
diff --git a/Documentation/litmus-tests/rcu/RCU+sync+read.litmus b/Documentation/litmus-tests/rcu/RCU+sync+read.litmus
new file mode 100644
index 0000000..f341767
--- /dev/null
+++ b/Documentation/litmus-tests/rcu/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 is one implication of the RCU grace-period guarantee, which says (among
+ * other things) that an RCU read-side critical section cannot span a grace period.
+ *)
+
+{
+int x = 0;
+int 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)
--
2.9.5