From: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
This commit adds a litmus test in which P0() and P1() form a lock-based S
litmus test, with the addition of P2(), which observes P0()'s and P1()'s
accesses with a full memory barrier but without the lock. This litmus
test asks whether writes carried out by two different processes under the
same lock will be seen in order by a third process not holding that lock.
The answer to this question is "yes" for all architectures supporting
the Linux kernel, but is "no" according to the current version of LKMM.
A patch to LKMM is under development.
Signed-off-by: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
---
.../ISA2+pooncelock+pooncelock+pombonce.litmus | 41 ++++++++++++++++++++++
1 file changed, 41 insertions(+)
create mode 100644 tools/memory-model/litmus-tests/ISA2+pooncelock+pooncelock+pombonce.litmus
diff --git a/tools/memory-model/litmus-tests/ISA2+pooncelock+pooncelock+pombonce.litmus b/tools/memory-model/litmus-tests/ISA2+pooncelock+pooncelock+pombonce.litmus
new file mode 100644
index 000000000000..7a39a0aaa976
--- /dev/null
+++ b/tools/memory-model/litmus-tests/ISA2+pooncelock+pooncelock+pombonce.litmus
@@ -0,0 +1,41 @@
+C ISA2+pooncelock+pooncelock+pombonce.litmus
+
+(*
+ * Result: Sometimes
+ *
+ * This test shows that the ordering provided by a lock-protected S
+ * litmus test (P0() and P1()) are not visible to external process P2().
+ * This is likely to change soon.
+ *)
+
+{}
+
+P0(int *x, int *y, spinlock_t *mylock)
+{
+ spin_lock(mylock);
+ WRITE_ONCE(*x, 1);
+ WRITE_ONCE(*y, 1);
+ spin_unlock(mylock);
+}
+
+P1(int *y, int *z, spinlock_t *mylock)
+{
+ int r0;
+
+ spin_lock(mylock);
+ r0 = READ_ONCE(*y);
+ WRITE_ONCE(*z, 1);
+ spin_unlock(mylock);
+}
+
+P2(int *x, int *z)
+{
+ int r1;
+ int r2;
+
+ r2 = READ_ONCE(*z);
+ smp_mb();
+ r1 = READ_ONCE(*x);
+}
+
+exists (1:r0=1 /\ 2:r2=1 /\ 2:r1=0)
--
2.5.2
