net: sched: remove qdisc->empty for lockless qdisc

As MISSED and DRAINING state are used to indicate a non-empty
qdisc, qdisc->empty is not longer needed, so remove it.

Acked-by: Jakub Kicinski <kuba@kernel.org>
Tested-by: Vladimir Oltean <vladimir.oltean@nxp.com> # flexcan
Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/sch_generic.h

@@ -117,8 +117,6 @@ struct Qdisc {
 	spinlock_t		busylock ____cacheline_aligned_in_smp;
 	spinlock_t		seqlock;
 
-	/* for NOLOCK qdisc, true if there are no enqueued skbs */
-	bool			empty;
 	struct rcu_head		rcu;
 
 	/* private data */
@@ -165,15 +163,15 @@ static inline bool qdisc_is_percpu_stats(const struct Qdisc *q)
 static inline bool qdisc_is_empty(const struct Qdisc *qdisc)
 {
 	if (qdisc_is_percpu_stats(qdisc))
-		return READ_ONCE(qdisc->empty);
+		return nolock_qdisc_is_empty(qdisc);
 	return !READ_ONCE(qdisc->q.qlen);
 }
 
 static inline bool qdisc_run_begin(struct Qdisc *qdisc)
 {
 	if (qdisc->flags & TCQ_F_NOLOCK) {
 		if (spin_trylock(&qdisc->seqlock))
-			goto nolock_empty;
+			return true;
 
 		/* If the MISSED flag is set, it means other thread has
 		 * set the MISSED flag before second spin_trylock(), so
@@ -195,12 +193,7 @@ static inline bool qdisc_run_begin(struct Qdisc *qdisc)
 		/* Retry again in case other CPU may not see the new flag
 		 * after it releases the lock at the end of qdisc_run_end().
 		 */
-		if (!spin_trylock(&qdisc->seqlock))
-			return false;
-
-nolock_empty:
-		WRITE_ONCE(qdisc->empty, false);
-		return true;
+		return spin_trylock(&qdisc->seqlock);
 	} else if (qdisc_is_running(qdisc)) {
 		return false;
 	}

net/sched/sch_generic.c

@@ -725,8 +725,6 @@ static struct sk_buff *pfifo_fast_dequeue(struct Qdisc *qdisc)
 		need_retry = false;
 
 		goto retry;
-	} else {
-		WRITE_ONCE(qdisc->empty, true);
 	}
 
 	return skb;
@@ -927,7 +925,6 @@ struct Qdisc *qdisc_alloc(struct netdev_queue *dev_queue,
 	sch->enqueue = ops->enqueue;
 	sch->dequeue = ops->dequeue;
 	sch->dev_queue = dev_queue;
-	sch->empty = true;
 	dev_hold(dev);
 	refcount_set(&sch->refcnt, 1);