rcu: Use rcu_segcblist_segempty() instead of open coding it

This makes the code more readable.

Reviewed-by: Qiuxu Zhuo <qiuxu.zhuo@intel.com>
Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>

Author: Frederic Weisbecker

kernel/rcu/rcu_segcblist.c

@@ -368,7 +368,7 @@ bool rcu_segcblist_entrain(struct rcu_segcblist *rsclp,
 	smp_mb(); /* Ensure counts are updated before callback is entrained. */
 	rhp->next = NULL;
 	for (i = RCU_NEXT_TAIL; i > RCU_DONE_TAIL; i--)
-		if (rsclp->tails[i] != rsclp->tails[i - 1])
+		if (!rcu_segcblist_segempty(rsclp, i))
 			break;
 	rcu_segcblist_inc_seglen(rsclp, i);
 	WRITE_ONCE(*rsclp->tails[i], rhp);
@@ -551,7 +551,7 @@ bool rcu_segcblist_accelerate(struct rcu_segcblist *rsclp, unsigned long seq)
 	 * as their ->gp_seq[] grace-period completion sequence number.
 	 */
 	for (i = RCU_NEXT_READY_TAIL; i > RCU_DONE_TAIL; i--)
-		if (rsclp->tails[i] != rsclp->tails[i - 1] &&
+		if (!rcu_segcblist_segempty(rsclp, i) &&
 		    ULONG_CMP_LT(rsclp->gp_seq[i], seq))
 			break;