net_sched: call qlen_notify only if child qdisc is empty

This callback is used for deactivating class in parent qdisc.
This is cheaper to test queue length right here.

Also this allows to catch draining screwed backlog and prevent
second deactivation of already inactive parent class which will
crash kernel for sure. Kernel with print warning at destruction
of child qdisc where no packets but backlog is not zero.

Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Signed-off-by: David S. Miller <davem@davemloft.net>

6 files changed, 15 insertions, 13 deletions

diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c
index 361377fbd780..0fea0c50b763 100644
--- a/net/sched/sch_api.c
+++ b/net/sched/sch_api.c
@@ -749,6 +749,7 @@ void qdisc_tree_reduce_backlog(struct Qdisc *sch, unsigned int n,
 	const struct Qdisc_class_ops *cops;
 	unsigned long cl;
 	u32 parentid;
+	bool notify;
 	int drops;
 
 	if (n == 0 && len == 0)
@@ -761,6 +762,13 @@ void qdisc_tree_reduce_backlog(struct Qdisc *sch, unsigned int n,
 
 		if (sch->flags & TCQ_F_NOPARENT)
 			break;
+		/* Notify parent qdisc only if child qdisc becomes empty.
+		 *
+		 * If child was empty even before update then backlog
+		 * counter is screwed and we skip notification because
+		 * parent class is already passive.
+		 */
+		notify = !sch->q.qlen && !WARN_ON_ONCE(!n);
 		/* TODO: perform the search on a per txq basis */
 		sch = qdisc_lookup(qdisc_dev(sch), TC_H_MAJ(parentid));
 		if (sch == NULL) {
@@ -768,7 +776,7 @@ void qdisc_tree_reduce_backlog(struct Qdisc *sch, unsigned int n,
 			break;
 		}
 		cops = sch->ops->cl_ops;
-		if (cops->qlen_notify) {
+		if (notify && cops->qlen_notify) {
 			cl = cops->get(sch, parentid);
 			cops->qlen_notify(sch, cl);
 			cops->put(sch, cl);
diff --git a/net/sched/sch_cbq.c b/net/sched/sch_cbq.c
index 780db43300b1..1bdb0106f342 100644
--- a/net/sched/sch_cbq.c
+++ b/net/sched/sch_cbq.c
@@ -1385,8 +1385,7 @@ static void cbq_qlen_notify(struct Qdisc *sch, unsigned long arg)
 {
 	struct cbq_class *cl = (struct cbq_class *)arg;
 
-	if (cl->q->q.qlen == 0)
-		cbq_deactivate_class(cl);
+	cbq_deactivate_class(cl);
 }
 
 static unsigned long cbq_get(struct Qdisc *sch, u32 classid)
diff --git a/net/sched/sch_drr.c b/net/sched/sch_drr.c
index a413dc1c2098..1d2f6235dfcf 100644
--- a/net/sched/sch_drr.c
+++ b/net/sched/sch_drr.c
@@ -246,8 +246,7 @@ static void drr_qlen_notify(struct Qdisc *csh, unsigned long arg)
 {
 	struct drr_class *cl = (struct drr_class *)arg;
 
-	if (cl->qdisc->q.qlen == 0)
-		list_del(&cl->alist);
+	list_del(&cl->alist);
 }
 
 static int drr_dump_class(struct Qdisc *sch, unsigned long arg,
diff --git a/net/sched/sch_hfsc.c b/net/sched/sch_hfsc.c
index fd15200f8627..14c99870cdb6 100644
--- a/net/sched/sch_hfsc.c
+++ b/net/sched/sch_hfsc.c
@@ -1221,10 +1221,8 @@ hfsc_qlen_notify(struct Qdisc *sch, unsigned long arg)
 {
 	struct hfsc_class *cl = (struct hfsc_class *)arg;
 
-	if (cl->qdisc->q.qlen == 0) {
-		update_vf(cl, 0, 0);
-		set_passive(cl);
-	}
+	update_vf(cl, 0, 0);
+	set_passive(cl);
 }
 
 static unsigned long
diff --git a/net/sched/sch_htb.c b/net/sched/sch_htb.c
index 5d65ec5207e9..dcf3c85e1f4f 100644
--- a/net/sched/sch_htb.c
+++ b/net/sched/sch_htb.c
@@ -1186,8 +1186,7 @@ static void htb_qlen_notify(struct Qdisc *sch, unsigned long arg)
 {
 	struct htb_class *cl = (struct htb_class *)arg;
 
-	if (cl->un.leaf.q->q.qlen == 0)
-		htb_deactivate(qdisc_priv(sch), cl);
+	htb_deactivate(qdisc_priv(sch), cl);
 }
 
 static unsigned long htb_get(struct Qdisc *sch, u32 classid)
diff --git a/net/sched/sch_qfq.c b/net/sched/sch_qfq.c
index 0e16dfda0bd7..9caa959f91e1 100644
--- a/net/sched/sch_qfq.c
+++ b/net/sched/sch_qfq.c
@@ -1428,8 +1428,7 @@ static void qfq_qlen_notify(struct Qdisc *sch, unsigned long arg)
 	struct qfq_sched *q = qdisc_priv(sch);
 	struct qfq_class *cl = (struct qfq_class *)arg;
 
-	if (cl->qdisc->q.qlen == 0)
-		qfq_deactivate_class(q, cl);
+	qfq_deactivate_class(q, cl);
 }
 
 static int qfq_init_qdisc(struct Qdisc *sch, struct nlattr *opt)