[PATCH 05/28] Documentation/litmus-tests: Add hazptr wildcard-flip escape test

[Kunwu Chan <kunwu.chan@gmail.com>]

Add a three-process litmus test for the in-flight wildcard window
of the single-pass scan: a straggling acquire which published the
old wildcard after the final walk cannot still load the
unpublished object.

Verified with herd7 (linux-kernel.cfg): Never 0 13.

Signed-off-by: Kunwu Chan <kunwu.chan@gmail.com>
Acked-by: Bradley Morgan <brads@mainlining.org>
---
 .../hazptr/hazptr-wildcard-flip-escape.litmus | 46 +++++++++++++++++++
 1 file changed, 46 insertions(+)
 create mode 100644 Documentation/litmus-tests/hazptr/hazptr-wildcard-flip-escape.litmus

diff --git a/Documentation/litmus-tests/hazptr/hazptr-wildcard-flip-escape.litmus b/Documentation/litmus-tests/hazptr/hazptr-wildcard-flip-escape.litmus
new file mode 100644
index 000000000000..de467bb82d20
--- /dev/null
+++ b/Documentation/litmus-tests/hazptr/hazptr-wildcard-flip-escape.litmus
@@ -0,0 +1,46 @@
+C hazptr-wildcard-flip-escape
+
+(*
+ * Result: Never
+ *
+ * Check that a straggling acquire which published the old
+ * wildcard after the final walk cannot still load the
+ * unpublished object.
+ *)
+
+{
+	int ptr = 3;
+	int hp = 0;
+	int wildcard = 1;
+	int enq = 0;
+}
+
+P0(int *ptr, int *enq)
+{
+	WRITE_ONCE(*ptr, 0);
+	smp_mb();
+	smp_store_release(enq, 1);
+}
+
+P1(int *enq, int *wildcard, int *hp)
+{
+	int r1;
+	int r2;
+
+	r1 = smp_load_acquire(enq);
+	WRITE_ONCE(*wildcard, 2);
+	r2 = READ_ONCE(*hp);
+}
+
+P2(int *wildcard, int *hp, int *ptr)
+{
+	int r0;
+	int r3;
+
+	r0 = READ_ONCE(*wildcard);
+	WRITE_ONCE(*hp, r0);
+	smp_mb();
+	r3 = READ_ONCE(*ptr);
+}
+
+exists (1:r1=1 /\ 1:r2=0 /\ 2:r3=3)
-- 
2.43.0