linux-kernel - [PATCH memory-model 3/3] tools/memory-model: litmus: Add two tests for unlock(A)+lock(B) ordering

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Date:   Wed,  1 Dec 2021 16:50:53 -0800
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        kernel-team@...com, mingo@...nel.org
Cc:     stern@...land.harvard.edu, parri.andrea@...il.com, will@...nel.org,
        peterz@...radead.org, boqun.feng@...il.com, npiggin@...il.com,
        dhowells@...hat.com, j.alglave@....ac.uk, luc.maranget@...ia.fr,
        akiyks@...il.com, "Paul E . McKenney" <paulmck@...nel.org>
Subject: [PATCH memory-model 3/3] tools/memory-model: litmus: Add two tests for unlock(A)+lock(B) ordering

From: Boqun Feng <boqun.feng@...il.com>

The memory model has been updated to provide a stronger ordering
guarantee for unlock(A)+lock(B) on the same CPU/thread. Therefore add
two litmus tests describing this new guarantee, these tests are simple
yet can clearly show the usage of the new guarantee, also they can serve
as the self tests for the modification in the model.

Co-developed-by: Alan Stern <stern@...land.harvard.edu>
Signed-off-by: Alan Stern <stern@...land.harvard.edu>
Signed-off-by: Boqun Feng <boqun.feng@...il.com>
Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
---
 ...LB+unlocklockonceonce+poacquireonce.litmus | 35 +++++++++++++++++++
 ...unlocklockonceonce+fencermbonceonce.litmus | 33 +++++++++++++++++
 tools/memory-model/litmus-tests/README        |  8 +++++
 3 files changed, 76 insertions(+)
 create mode 100644 tools/memory-model/litmus-tests/LB+unlocklockonceonce+poacquireonce.litmus
 create mode 100644 tools/memory-model/litmus-tests/MP+unlocklockonceonce+fencermbonceonce.litmus

diff --git a/tools/memory-model/litmus-tests/LB+unlocklockonceonce+poacquireonce.litmus b/tools/memory-model/litmus-tests/LB+unlocklockonceonce+poacquireonce.litmus
new file mode 100644
index 0000000000000..eb34123a6ffe0
--- /dev/null
+++ b/tools/memory-model/litmus-tests/LB+unlocklockonceonce+poacquireonce.litmus
@@ -0,0 +1,35 @@
+C LB+unlocklockonceonce+poacquireonce
+
+(*
+ * Result: Never
+ *
+ * If two locked critical sections execute on the same CPU, all accesses
+ * in the first must execute before any accesses in the second, even if the
+ * critical sections are protected by different locks.  Note: Even when a
+ * write executes before a read, their memory effects can be reordered from
+ * the viewpoint of another CPU (the kind of reordering allowed by TSO).
+ *)
+
+{}
+
+P0(spinlock_t *s, spinlock_t *t, int *x, int *y)
+{
+	int r1;
+
+	spin_lock(s);
+	r1 = READ_ONCE(*x);
+	spin_unlock(s);
+	spin_lock(t);
+	WRITE_ONCE(*y, 1);
+	spin_unlock(t);
+}
+
+P1(int *x, int *y)
+{
+	int r2;
+
+	r2 = smp_load_acquire(y);
+	WRITE_ONCE(*x, 1);
+}
+
+exists (0:r1=1 /\ 1:r2=1)
diff --git a/tools/memory-model/litmus-tests/MP+unlocklockonceonce+fencermbonceonce.litmus b/tools/memory-model/litmus-tests/MP+unlocklockonceonce+fencermbonceonce.litmus
new file mode 100644
index 0000000000000..2feb1398be716
--- /dev/null
+++ b/tools/memory-model/litmus-tests/MP+unlocklockonceonce+fencermbonceonce.litmus
@@ -0,0 +1,33 @@
+C MP+unlocklockonceonce+fencermbonceonce
+
+(*
+ * Result: Never
+ *
+ * If two locked critical sections execute on the same CPU, stores in the
+ * first must propagate to each CPU before stores in the second do, even if
+ * the critical sections are protected by different locks.
+ *)
+
+{}
+
+P0(spinlock_t *s, spinlock_t *t, int *x, int *y)
+{
+	spin_lock(s);
+	WRITE_ONCE(*x, 1);
+	spin_unlock(s);
+	spin_lock(t);
+	WRITE_ONCE(*y, 1);
+	spin_unlock(t);
+}
+
+P1(int *x, int *y)
+{
+	int r1;
+	int r2;
+
+	r1 = READ_ONCE(*y);
+	smp_rmb();
+	r2 = READ_ONCE(*x);
+}
+
+exists (1:r1=1 /\ 1:r2=0)
diff --git a/tools/memory-model/litmus-tests/README b/tools/memory-model/litmus-tests/README
index 681f9067fa9ed..d311a0ff1ae64 100644
--- a/tools/memory-model/litmus-tests/README
+++ b/tools/memory-model/litmus-tests/README
@@ -63,6 +63,10 @@ LB+poonceonces.litmus
 	As above, but with store-release replaced with WRITE_ONCE()
 	and load-acquire replaced with READ_ONCE().
 
+LB+unlocklockonceonce+poacquireonce.litmus
+	Does a unlock+lock pair provides ordering guarantee between a
+	load and a store?
+
 MP+onceassign+derefonce.litmus
 	As below, but with rcu_assign_pointer() and an rcu_dereference().
 
@@ -90,6 +94,10 @@ MP+porevlocks.litmus
 	As below, but with the first access of the writer process
 	and the second access of reader process protected by a lock.
 
+MP+unlocklockonceonce+fencermbonceonce.litmus
+	Does a unlock+lock pair provides ordering guarantee between a
+	store and another store?
+
 MP+fencewmbonceonce+fencermbonceonce.litmus
 	Does a smp_wmb() (between the stores) and an smp_rmb() (between
 	the loads) suffice for the message-passing litmus test, where one
-- 
2.31.1.189.g2e36527f23