netdev - [PATCH] net: sched: fix ordering of qlen adjustment

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Message-ID: <6c7ae1c8-8573-4f4a-96cb-0a75eab21516@gmail.com>
Date: Mon, 2 Dec 2024 17:22:57 +0100
From: Lion Ackermann <nnamrec@...il.com>
To: netdev@...r.kernel.org
Cc: toke@...e.dk, jhs@...atatu.com, xiyou.wangcong@...il.com,
 jiri@...nulli.us, davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
 pabeni@...hat.com, nnamrec@...il.com
Subject: [PATCH] net: sched: fix ordering of qlen adjustment

Changes to sch->q.qlen around qdisc_tree_reduce_backlog() need to happen
_before_ a call to said function because otherwise it may fail to notify
parent qdiscs when the child is about to become empty.

Signed-off-by: Lion Ackermann <nnamrec@...il.com>
---
 net/sched/sch_cake.c  | 2 +-
 net/sched/sch_choke.c | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/sched/sch_cake.c b/net/sched/sch_cake.c
index 30955dd45779..a65fad45d556 100644
--- a/net/sched/sch_cake.c
+++ b/net/sched/sch_cake.c
@@ -1542,7 +1542,6 @@ static unsigned int cake_drop(struct Qdisc *sch, struct sk_buff **to_free)
 	b->backlogs[idx]    -= len;
 	b->tin_backlog      -= len;
 	sch->qstats.backlog -= len;
-	qdisc_tree_reduce_backlog(sch, 1, len);
 
 	flow->dropped++;
 	b->tin_dropped++;
@@ -1553,6 +1552,7 @@ static unsigned int cake_drop(struct Qdisc *sch, struct sk_buff **to_free)
 
 	__qdisc_drop(skb, to_free);
 	sch->q.qlen--;
+	qdisc_tree_reduce_backlog(sch, 1, len);
 
 	cake_heapify(q, 0);
 
diff --git a/net/sched/sch_choke.c b/net/sched/sch_choke.c
index 19c851125901..a91959142208 100644
--- a/net/sched/sch_choke.c
+++ b/net/sched/sch_choke.c
@@ -123,10 +123,10 @@ static void choke_drop_by_idx(struct Qdisc *sch, unsigned int idx,
 	if (idx == q->tail)
 		choke_zap_tail_holes(q);
 
+	--sch->q.qlen;
 	qdisc_qstats_backlog_dec(sch, skb);
 	qdisc_tree_reduce_backlog(sch, 1, qdisc_pkt_len(skb));
 	qdisc_drop(skb, sch, to_free);
-	--sch->q.qlen;
 }
 
 struct choke_skb_cb {
-- 
2.47.0