Merge branch 'lkmm-dev.2022.10.18c' into HEAD

lkmm-dev.2022.10.18c: LKMM development branch

Author: paulmckrcu

Documentation/litmus-tests/locking/DCL-broken.litmus

@@ -0,0 +1,55 @@
+C DCL-broken
+
+(*
+ * Result: Sometimes
+ *
+ * This litmus test demonstrates more than just locking is required to
+ * correctly implement double-checked locking.
+ *)
+
+{
+	int flag;
+	int data;
+	int lck;
+}
+
+P0(int *flag, int *data, int *lck)
+{
+	int r0;
+	int r1;
+	int r2;
+
+	r0 = READ_ONCE(*flag);
+	if (r0 == 0) {
+		spin_lock(lck);
+		r1 = READ_ONCE(*flag);
+		if (r1 == 0) {
+			WRITE_ONCE(*data, 1);
+			WRITE_ONCE(*flag, 1);
+		}
+		spin_unlock(lck);
+	}
+	r2 = READ_ONCE(*data);
+}
+
+P1(int *flag, int *data, int *lck)
+{
+	int r0;
+	int r1;
+	int r2;
+
+	r0 = READ_ONCE(*flag);
+	if (r0 == 0) {
+		spin_lock(lck);
+		r1 = READ_ONCE(*flag);
+		if (r1 == 0) {
+			WRITE_ONCE(*data, 1);
+			WRITE_ONCE(*flag, 1);
+		}
+		spin_unlock(lck);
+	}
+	r2 = READ_ONCE(*data);
+}
+
+locations [flag;data;lck;0:r0;0:r1;1:r0;1:r1]
+exists (0:r2=0 \/ 1:r2=0)

Documentation/litmus-tests/locking/DCL-fixed.litmus

@@ -0,0 +1,56 @@
+C DCL-fixed
+
+(*
+ * Result: Never
+ *
+ * This litmus test demonstrates that double-checked locking can be
+ * reliable given proper use of smp_load_acquire() and smp_store_release()
+ * in addition to the locking.
+ *)
+
+{
+	int flag;
+	int data;
+	int lck;
+}
+
+P0(int *flag, int *data, int *lck)
+{
+	int r0;
+	int r1;
+	int r2;
+
+	r0 = smp_load_acquire(flag);
+	if (r0 == 0) {
+		spin_lock(lck);
+		r1 = READ_ONCE(*flag);
+		if (r1 == 0) {
+			WRITE_ONCE(*data, 1);
+			smp_store_release(flag, 1);
+		}
+		spin_unlock(lck);
+	}
+	r2 = READ_ONCE(*data);
+}
+
+P1(int *flag, int *data, int *lck)
+{
+	int r0;
+	int r1;
+	int r2;
+
+	r0 = smp_load_acquire(flag);
+	if (r0 == 0) {
+		spin_lock(lck);
+		r1 = READ_ONCE(*flag);
+		if (r1 == 0) {
+			WRITE_ONCE(*data, 1);
+			smp_store_release(flag, 1);
+		}
+		spin_unlock(lck);
+	}
+	r2 = READ_ONCE(*data);
+}
+
+locations [flag;data;lck;0:r0;0:r1;1:r0;1:r1]
+exists (0:r2=0 \/ 1:r2=0)

Documentation/litmus-tests/locking/RM-broken.litmus

@@ -0,0 +1,42 @@
+C RM-broken
+
+(*
+ * Result: DEADLOCK
+ *
+ * This litmus test demonstrates that the old "roach motel" approach
+ * to locking, where code can be freely moved into critical sections,
+ * cannot be used in the Linux kernel.
+ *)
+
+{
+	int lck;
+	int x;
+	int y;
+}
+
+P0(int *x, int *y, int *lck)
+{
+	int r2;
+
+	spin_lock(lck);
+	r2 = atomic_inc_return(y);
+	WRITE_ONCE(*x, 1);
+	spin_unlock(lck);
+}
+
+P1(int *x, int *y, int *lck)
+{
+	int r0;
+	int r1;
+	int r2;
+
+	spin_lock(lck);
+	r0 = READ_ONCE(*x);
+	r1 = READ_ONCE(*x);
+	r2 = atomic_inc_return(y);
+	spin_unlock(lck);
+}
+
+locations [x;lck;0:r2;1:r0;1:r1;1:r2]
+filter (y=2 /\ 1:r0=0 /\ 1:r1=1)
+exists (1:r2=1)

Documentation/litmus-tests/locking/RM-fixed.litmus

@@ -0,0 +1,42 @@
+C RM-fixed
+
+(*
+ * Result: Never
+ *
+ * This litmus test demonstrates that the old "roach motel" approach
+ * to locking, where code can be freely moved into critical sections,
+ * cannot be used in the Linux kernel.
+ *)
+
+{
+	int lck;
+	int x;
+	int y;
+}
+
+P0(int *x, int *y, int *lck)
+{
+	int r2;
+
+	spin_lock(lck);
+	r2 = atomic_inc_return(y);
+	WRITE_ONCE(*x, 1);
+	spin_unlock(lck);
+}
+
+P1(int *x, int *y, int *lck)
+{
+	int r0;
+	int r1;
+	int r2;
+
+	r0 = READ_ONCE(*x);
+	r1 = READ_ONCE(*x);
+	spin_lock(lck);
+	r2 = atomic_inc_return(y);
+	spin_unlock(lck);
+}
+
+locations [x;lck;0:r2;1:r0;1:r1;1:r2]
+filter (y=2 /\ 1:r0=0 /\ 1:r1=1)
+exists (1:r2=1)