Merge branch 'net_sched-adapt-qdiscs-for-reentrant-enqueue-cases'

Victor Nogueira says:

====================
net_sched: Adapt qdiscs for reentrant enqueue cases

As described in Gerrard's report [1], there are cases where netem can
make the qdisc enqueue callback reentrant. Some qdiscs (drr, hfsc, ets,
qfq) break whenever the enqueue callback has reentrant behaviour.
This series addresses these issues by adding extra checks that cater for
these reentrant corner cases. This series has passed all relevant test
cases in the TDC suite.

[1] https://lore.kernel.org/netdev/CAHcdcOm+03OD2j6R0=YHKqmy=VgJ8xEOKuP6c7mSgnp-TEJJbw@mail.gmail.com/
====================

Link: https://patch.msgid.link/20250425220710.3964791-1-victor@mojatatu.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

4 files changed, 20 insertions, 11 deletions

diff --git a/net/sched/sch_drr.c b/net/sched/sch_drr.c
index e0a81d313aa7..9b6d79bd8737 100644
--- a/net/sched/sch_drr.c
+++ b/net/sched/sch_drr.c
@@ -35,6 +35,11 @@ struct drr_sched {
 	struct Qdisc_class_hash		clhash;
 };
 
+static bool cl_is_active(struct drr_class *cl)
+{
+	return !list_empty(&cl->alist);
+}
+
 static struct drr_class *drr_find_class(struct Qdisc *sch, u32 classid)
 {
 	struct drr_sched *q = qdisc_priv(sch);
@@ -337,7 +342,6 @@ static int drr_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 	struct drr_sched *q = qdisc_priv(sch);
 	struct drr_class *cl;
 	int err = 0;
-	bool first;
 
 	cl = drr_classify(skb, sch, &err);
 	if (cl == NULL) {
@@ -347,7 +351,6 @@ static int drr_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 		return err;
 	}
 
-	first = !cl->qdisc->q.qlen;
 	err = qdisc_enqueue(skb, cl->qdisc, to_free);
 	if (unlikely(err != NET_XMIT_SUCCESS)) {
 		if (net_xmit_drop_count(err)) {
@@ -357,7 +360,7 @@ static int drr_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 		return err;
 	}
 
-	if (first) {
+	if (!cl_is_active(cl)) {
 		list_add_tail(&cl->alist, &q->active);
 		cl->deficit = cl->quantum;
 	}
diff --git a/net/sched/sch_ets.c b/net/sched/sch_ets.c
index c3bdeb14185b..2c069f0181c6 100644
--- a/net/sched/sch_ets.c
+++ b/net/sched/sch_ets.c
@@ -74,6 +74,11 @@ static const struct nla_policy ets_class_policy[TCA_ETS_MAX + 1] = {
 	[TCA_ETS_QUANTA_BAND] = { .type = NLA_U32 },
 };
 
+static bool cl_is_active(struct ets_class *cl)
+{
+	return !list_empty(&cl->alist);
+}
+
 static int ets_quantum_parse(struct Qdisc *sch, const struct nlattr *attr,
 			     unsigned int *quantum,
 			     struct netlink_ext_ack *extack)
@@ -416,7 +421,6 @@ static int ets_qdisc_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 	struct ets_sched *q = qdisc_priv(sch);
 	struct ets_class *cl;
 	int err = 0;
-	bool first;
 
 	cl = ets_classify(skb, sch, &err);
 	if (!cl) {
@@ -426,7 +430,6 @@ static int ets_qdisc_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 		return err;
 	}
 
-	first = !cl->qdisc->q.qlen;
 	err = qdisc_enqueue(skb, cl->qdisc, to_free);
 	if (unlikely(err != NET_XMIT_SUCCESS)) {
 		if (net_xmit_drop_count(err)) {
@@ -436,7 +439,7 @@ static int ets_qdisc_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 		return err;
 	}
 
-	if (first && !ets_class_is_strict(q, cl)) {
+	if (!cl_is_active(cl) && !ets_class_is_strict(q, cl)) {
 		list_add_tail(&cl->alist, &q->active);
 		cl->deficit = cl->quantum;
 	}
diff --git a/net/sched/sch_hfsc.c b/net/sched/sch_hfsc.c
index 6c8ef826cec0..cb8c525ea20e 100644
--- a/net/sched/sch_hfsc.c
+++ b/net/sched/sch_hfsc.c
@@ -1569,7 +1569,7 @@ hfsc_enqueue(struct sk_buff *skb, struct Qdisc *sch, struct sk_buff **to_free)
 		return err;
 	}
 
-	if (first) {
+	if (first && !cl->cl_nactive) {
 		if (cl->cl_flags & HFSC_RSC)
 			init_ed(cl, len);
 		if (cl->cl_flags & HFSC_FSC)
diff --git a/net/sched/sch_qfq.c b/net/sched/sch_qfq.c
index 687a932eb9b2..bf1282cb22eb 100644
--- a/net/sched/sch_qfq.c
+++ b/net/sched/sch_qfq.c
@@ -202,6 +202,11 @@ struct qfq_sched {
  */
 enum update_reason {enqueue, requeue};
 
+static bool cl_is_active(struct qfq_class *cl)
+{
+	return !list_empty(&cl->alist);
+}
+
 static struct qfq_class *qfq_find_class(struct Qdisc *sch, u32 classid)
 {
 	struct qfq_sched *q = qdisc_priv(sch);
@@ -1215,7 +1220,6 @@ static int qfq_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 	struct qfq_class *cl;
 	struct qfq_aggregate *agg;
 	int err = 0;
-	bool first;
 
 	cl = qfq_classify(skb, sch, &err);
 	if (cl == NULL) {
@@ -1237,7 +1241,6 @@ static int qfq_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 	}
 
 	gso_segs = skb_is_gso(skb) ? skb_shinfo(skb)->gso_segs : 1;
-	first = !cl->qdisc->q.qlen;
 	err = qdisc_enqueue(skb, cl->qdisc, to_free);
 	if (unlikely(err != NET_XMIT_SUCCESS)) {
 		pr_debug("qfq_enqueue: enqueue failed %d\n", err);
@@ -1253,8 +1256,8 @@ static int qfq_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 	++sch->q.qlen;
 
 	agg = cl->agg;
-	/* if the queue was not empty, then done here */
-	if (!first) {
+	/* if the class is active, then done here */
+	if (cl_is_active(cl)) {
 		if (unlikely(skb == cl->qdisc->ops->peek(cl->qdisc)) &&
 		    list_first_entry(&agg->active, struct qfq_class, alist)
 		    == cl && cl->deficit < len)