rcu: Consolidate expedited GP tracing into rcu_exp_gp_seq_snap()

This commit moves some duplicate code from synchronize_rcu_expedited()
and synchronize_sched_expedited() into rcu_exp_gp_seq_snap().  This
doesn't save lines of code, but does eliminate a "tell me twice" issue.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

kernel/rcu/tree.c

@@ -3392,8 +3392,12 @@ static void rcu_exp_gp_seq_end(struct rcu_state *rsp)
 }
 static unsigned long rcu_exp_gp_seq_snap(struct rcu_state *rsp)
 {
+	unsigned long s;
+
 	smp_mb(); /* Caller's modifications seen first by other CPUs. */
-	return rcu_seq_snap(&rsp->expedited_sequence);
+	s = rcu_seq_snap(&rsp->expedited_sequence);
+	trace_rcu_exp_grace_period(rsp->name, s, TPS("snap"));
+	return s;
 }
 static bool rcu_exp_gp_seq_done(struct rcu_state *rsp, unsigned long s)
 {
@@ -3898,8 +3902,6 @@ void synchronize_sched_expedited(void)
 
 	/* Take a snapshot of the sequence number.  */
 	s = rcu_exp_gp_seq_snap(rsp);
-	trace_rcu_exp_grace_period(rsp->name, s, TPS("snap"));
-
 	if (exp_funnel_lock(rsp, s))
 		return;  /* Someone else did our work for us. */
 

kernel/rcu/tree_plugin.h

@@ -748,8 +748,6 @@ void synchronize_rcu_expedited(void)
 	}
 
 	s = rcu_exp_gp_seq_snap(rsp);
-	trace_rcu_exp_grace_period(rsp->name, s, TPS("snap"));
-
 	if (exp_funnel_lock(rsp, s))
 		return;  /* Someone else did our work for us. */