rcu: Don't kick unless grace period or request

The current code can result in spurious kicks when there are no grace
periods in progress and no grace-period-related requests.  This is
sort of OK for a diagnostic aid, but the resulting ftrace-dump messages
in dmesg are annoying.  This commit therefore avoids spurious kicks
in the common case.
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: NJosh Triplett <josh@joshtriplett.org>

kernel/rcu/tree.c

@@ -1304,7 +1304,8 @@ static void rcu_stall_kick_kthreads(struct rcu_state *rsp)
 	if (!rcu_kick_kthreads)
 		return;
 	j = READ_ONCE(rsp->jiffies_kick_kthreads);
-	if (time_after(jiffies, j) && rsp->gp_kthread) {
+	if (time_after(jiffies, j) && rsp->gp_kthread &&
+	    (rcu_gp_in_progress(rsp) || READ_ONCE(rsp->gp_flags))) {
 		WARN_ONCE(1, "Kicking %s grace-period kthread\n", rsp->name);
 		rcu_ftrace_dump(DUMP_ALL);
 		wake_up_process(rsp->gp_kthread);