rcutorture: Use rcu_gp_slow_register/unregister() only for rcutype test

The rcu_gp_slow_register/unregister() is only useful in tests where
torture_type=rcu, so this commit therefore generates ->gp_slow_register()
and ->gp_slow_unregister() function pointers in the rcu_torture_ops
structure, and slows grace periods only when these function pointers
exist.

Signed-off-by: Zqiang <qiang.zhang1211@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>

kernel/rcu/rcutorture.c

@@ -382,6 +382,8 @@ struct rcu_torture_ops {
 	bool (*check_boost_failed)(unsigned long gp_state, int *cpup);
 	int (*stall_dur)(void);
 	void (*get_gp_data)(int *flags, unsigned long *gp_seq);
+	void (*gp_slow_register)(atomic_t *rgssp);
+	void (*gp_slow_unregister)(atomic_t *rgssp);
 	long cbflood_max;
 	int irq_capable;
 	int can_boost;
@@ -570,6 +572,8 @@ static struct rcu_torture_ops rcu_ops = {
 	.check_boost_failed	= rcu_check_boost_fail,
 	.stall_dur		= rcu_jiffies_till_stall_check,
 	.get_gp_data		= rcutorture_get_gp_data,
+	.gp_slow_register	= rcu_gp_slow_register,
+	.gp_slow_unregister	= rcu_gp_slow_unregister,
 	.irq_capable		= 1,
 	.can_boost		= IS_ENABLED(CONFIG_RCU_BOOST),
 	.extendables		= RCUTORTURE_MAX_EXTEND,
@@ -3343,12 +3347,12 @@ rcu_torture_cleanup(void)
 			pr_info("%s: Invoking %pS().\n", __func__, cur_ops->cb_barrier);
 			cur_ops->cb_barrier();
 		}
-		rcu_gp_slow_unregister(NULL);
+		if (cur_ops->gp_slow_unregister)
+			cur_ops->gp_slow_unregister(NULL);
 		return;
 	}
 	if (!cur_ops) {
 		torture_cleanup_end();
-		rcu_gp_slow_unregister(NULL);
 		return;
 	}
 
@@ -3447,7 +3451,8 @@ rcu_torture_cleanup(void)
 	else
 		rcu_torture_print_module_parms(cur_ops, "End of test: SUCCESS");
 	torture_cleanup_end();
-	rcu_gp_slow_unregister(&rcu_fwd_cb_nodelay);
+	if (cur_ops->gp_slow_unregister)
+		cur_ops->gp_slow_unregister(NULL);
 }
 
 #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
@@ -3929,7 +3934,8 @@ rcu_torture_init(void)
 	if (object_debug)
 		rcu_test_debug_objects();
 	torture_init_end();
-	rcu_gp_slow_register(&rcu_fwd_cb_nodelay);
+	if (cur_ops->gp_slow_register && !WARN_ON_ONCE(!cur_ops->gp_slow_unregister))
+		cur_ops->gp_slow_register(&rcu_fwd_cb_nodelay);
 	return 0;
 
 unwind: