[Patch net 04/12] sch_qfq: make qfq_qlen_notify() idempotent

Cong Wang
2025-03-20T23:25:53Z

qfq_qlen_notify() always deletes its class from its active list
with list_del_init() _and_ calls qfq_deactivate_agg() when the whole list
becomes empty.

To make it idempotent, just skip everything when it is not in the active
list.

Also change other list_del()'s to list_del_init() just to be extra safe.

Reported-by: Gerrard Tai <gerrard.tai@starlabs.sg>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
---
net/sched/sch_qfq.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/net/sched/sch_qfq.c b/net/sched/sch_qfq.c
index 6a07cdbdb9e1..9f8e1ada058c 100644
--- a/net/sched/sch_qfq.c
+++ b/net/sched/sch_qfq.c
@@ -347,7 +347,7 @@ static void qfq_deactivate_class(struct qfq_sched *q, struct qfq_class *cl)
struct qfq_aggregate *agg = cl->agg;

- list_del(&cl->alist); /* remove from RR queue of the aggregate */
+ list_del_init(&cl->alist); /* remove from RR queue of the aggregate */
if (list_empty(&agg->active)) /* agg is now inactive */
qfq_deactivate_agg(q, agg);
}
@@ -474,6 +474,7 @@ static int qfq_change_class(struct Qdisc *sch, u32 classid, u32 parentid,
gnet_stats_basic_sync_init(&cl->bstats);
cl->common.classid = classid;
cl->deficit = lmax;
+ INIT_LIST_HEAD(&cl->alist);

cl->qdisc = qdisc_create_dflt(sch->dev_queue, &pfifo_qdisc_ops,
classid, NULL);
@@ -982,7 +983,7 @@ static struct sk_buff *agg_dequeue(struct qfq_aggregate *agg,
cl->deficit -= (int) len;

if (cl->qdisc->q.qlen == 0) /* no more packets, remove from list */
- list_del(&cl->alist);
+ list_del_init(&cl->alist);
else if (cl->deficit < qdisc_pkt_len(cl->qdisc->ops->peek(cl->qdisc))) {
cl->deficit += agg->lmax;
list_move_tail(&cl->alist, &agg->active);
@@ -1415,6 +1416,8 @@ 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 (list_empty(&cl->alist))
+ return;
qfq_deactivate_class(q, cl);
}

--
2.34.1