Merge branch 'net_sched-no-longer-use-qdisc_tree_flush_backlog'

Eric Dumazet says:

====================
net_sched: no longer use qdisc_tree_flush_backlog()

This series is based on a report from Gerrard Tai.

Essentially, all users of qdisc_tree_flush_backlog() are racy.

We must instead use qdisc_purge_queue().
====================

Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

Author: kuba-moo

include/net/sch_generic.h

@@ -973,14 +973,6 @@ static inline void qdisc_qstats_qlen_backlog(struct Qdisc *sch,  __u32 *qlen,
 	*backlog = qstats.backlog;
 }
 
-static inline void qdisc_tree_flush_backlog(struct Qdisc *sch)
-{
-	__u32 qlen, backlog;
-
-	qdisc_qstats_qlen_backlog(sch, &qlen, &backlog);
-	qdisc_tree_reduce_backlog(sch, qlen, backlog);
-}
-
 static inline void qdisc_purge_queue(struct Qdisc *sch)
 {
 	__u32 qlen, backlog;

net/sched/sch_ets.c

@@ -661,7 +661,7 @@ static int ets_qdisc_change(struct Qdisc *sch, struct nlattr *opt,
 	for (i = q->nbands; i < oldbands; i++) {
 		if (i >= q->nstrict && q->classes[i].qdisc->q.qlen)
 			list_del_init(&q->classes[i].alist);
-		qdisc_tree_flush_backlog(q->classes[i].qdisc);
+		qdisc_purge_queue(q->classes[i].qdisc);
 	}
 	WRITE_ONCE(q->nstrict, nstrict);
 	memcpy(q->prio2band, priomap, sizeof(priomap));

net/sched/sch_prio.c

@@ -211,7 +211,7 @@ static int prio_tune(struct Qdisc *sch, struct nlattr *opt,
 	memcpy(q->prio2band, qopt->priomap, TC_PRIO_MAX+1);
 
 	for (i = q->bands; i < oldbands; i++)
-		qdisc_tree_flush_backlog(q->queues[i]);
+		qdisc_purge_queue(q->queues[i]);
 
 	for (i = oldbands; i < q->bands; i++) {
 		q->queues[i] = queues[i];

net/sched/sch_red.c

@@ -285,7 +285,7 @@ static int __red_change(struct Qdisc *sch, struct nlattr **tb,
 	q->userbits = userbits;
 	q->limit = ctl->limit;
 	if (child) {
-		qdisc_tree_flush_backlog(q->qdisc);
+		qdisc_purge_queue(q->qdisc);
 		old_child = q->qdisc;
 		q->qdisc = child;
 	}

net/sched/sch_tbf.c

@@ -452,7 +452,7 @@ static int tbf_change(struct Qdisc *sch, struct nlattr *opt,
 
 	sch_tree_lock(sch);
 	if (child) {
-		qdisc_tree_flush_backlog(q->qdisc);
+		qdisc_purge_queue(q->qdisc);
 		old = q->qdisc;
 		q->qdisc = child;
 	}