refscale: Add srcu_read_lock_lite() support using "srcu-lite"

This commit creates a new srcu-lite option for the refscale.scale_type
module parameter that selects srcu_read_lock_lite() and
srcu_read_unlock_lite().

[ paulmck: Apply Dan Carpenter feedback. ]

Signed-off-by: Paul E. McKenney <[email protected]>
Cc: Alexei Starovoitov <[email protected]>
Cc: Andrii Nakryiko <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Kent Overstreet <[email protected]>
Cc: <[email protected]>
Reviewed-by: Neeraj Upadhyay <[email protected]>
Signed-off-by: Frederic Weisbecker <[email protected]>

Author: paulmckrcu

kernel/rcu/refscale.c

@@ -212,6 +212,36 @@ static const struct ref_scale_ops srcu_ops = {
 	.name		= "srcu"
 };
 
+static void srcu_lite_ref_scale_read_section(const int nloops)
+{
+	int i;
+	int idx;
+
+	for (i = nloops; i >= 0; i--) {
+		idx = srcu_read_lock_lite(srcu_ctlp);
+		srcu_read_unlock_lite(srcu_ctlp, idx);
+	}
+}
+
+static void srcu_lite_ref_scale_delay_section(const int nloops, const int udl, const int ndl)
+{
+	int i;
+	int idx;
+
+	for (i = nloops; i >= 0; i--) {
+		idx = srcu_read_lock_lite(srcu_ctlp);
+		un_delay(udl, ndl);
+		srcu_read_unlock_lite(srcu_ctlp, idx);
+	}
+}
+
+static const struct ref_scale_ops srcu_lite_ops = {
+	.init		= rcu_sync_scale_init,
+	.readsection	= srcu_lite_ref_scale_read_section,
+	.delaysection	= srcu_lite_ref_scale_delay_section,
+	.name		= "srcu-lite"
+};
+
 #ifdef CONFIG_TASKS_RCU
 
 // Definitions for RCU Tasks ref scale testing: Empty read markers.
@@ -1082,9 +1112,10 @@ ref_scale_init(void)
 	long i;
 	int firsterr = 0;
 	static const struct ref_scale_ops *scale_ops[] = {
-		&rcu_ops, &srcu_ops, RCU_TRACE_OPS RCU_TASKS_OPS &refcnt_ops, &rwlock_ops,
-		&rwsem_ops, &lock_ops, &lock_irq_ops, &acqrel_ops, &clock_ops, &jiffies_ops,
-		&typesafe_ref_ops, &typesafe_lock_ops, &typesafe_seqlock_ops,
+		&rcu_ops, &srcu_ops, &srcu_lite_ops, RCU_TRACE_OPS RCU_TASKS_OPS
+		&refcnt_ops, &rwlock_ops, &rwsem_ops, &lock_ops, &lock_irq_ops, &acqrel_ops,
+		&clock_ops, &jiffies_ops, &typesafe_ref_ops, &typesafe_lock_ops,
+		&typesafe_seqlock_ops,
 	};
 
 	if (!torture_init_begin(scale_type, verbose))