rcu: Remove !PREEMPT code from rcu_note_voluntary_context_switch()

Because RCU-tasks exists only in PREEMPT kernels and because RCU-sched
no longer exists in PREEMPT kernels, it is no longer necessary for the
rcu_note_voluntary_context_switch() macro to do anything for !PREEMPT
kernels.  This commit therefore removes !PREEMPT-related code from
this macro, namely, the rcu_all_qs().
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

include/linux/rcupdate.h

@@ -150,18 +150,14 @@ static inline void rcu_init_nohz(void) { }
 		if (READ_ONCE((t)->rcu_tasks_holdout)) \
 			WRITE_ONCE((t)->rcu_tasks_holdout, false); \
 	} while (0)
-#define rcu_note_voluntary_context_switch(t) \
-	do { \
-		rcu_all_qs(); \
-		rcu_tasks_qs(t); \
-	} while (0)
+#define rcu_note_voluntary_context_switch(t) rcu_tasks_qs(t)
 void call_rcu_tasks(struct rcu_head *head, rcu_callback_t func);
 void synchronize_rcu_tasks(void);
 void exit_tasks_rcu_start(void);
 void exit_tasks_rcu_finish(void);
 #else /* #ifdef CONFIG_TASKS_RCU */
 #define rcu_tasks_qs(t)	do { } while (0)
-#define rcu_note_voluntary_context_switch(t)		rcu_all_qs()
+#define rcu_note_voluntary_context_switch(t) do { } while (0)
 #define call_rcu_tasks call_rcu
 #define synchronize_rcu_tasks synchronize_rcu
 static inline void exit_tasks_rcu_start(void) { }