linux-kernel - [PATCH AUTOSEL 5.4 5/7] net: sched: fix ordering of qlen adjustment

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Message-ID: <20241211185442.3843374-5-sashal@kernel.org>
Date: Wed, 11 Dec 2024 13:54:38 -0500
From: Sasha Levin <sashal@...nel.org>
To: linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Cc: Lion Ackermann <nnamrec@...il.com>,
	Toke Høiland-Jørgensen <toke@...e.dk>,
	"David S . Miller" <davem@...emloft.net>,
	Sasha Levin <sashal@...nel.org>,
	jhs@...atatu.com,
	xiyou.wangcong@...il.com,
	jiri@...nulli.us,
	edumazet@...gle.com,
	kuba@...nel.org,
	pabeni@...hat.com,
	cake@...ts.bufferbloat.net,
	netdev@...r.kernel.org
Subject: [PATCH AUTOSEL 5.4 5/7] net: sched: fix ordering of qlen adjustment

From: Lion Ackermann <nnamrec@...il.com>

[ Upstream commit 5eb7de8cd58e73851cd37ff8d0666517d9926948 ]

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>
Acked-by: Toke Høiland-Jørgensen <toke@...e.dk>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 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 9b4a9bdbeafd9..f2a49bccb5ef5 100644
--- a/net/sched/sch_cake.c
+++ b/net/sched/sch_cake.c
@@ -1505,7 +1505,6 @@ 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++;
@@ -1516,6 +1515,7 @@ 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 e54f6eabfa0c0..2007bc4f96709 100644
--- a/net/sched/sch_choke.c
+++ b/net/sched/sch_choke.c
@@ -124,10 +124,10 @@ 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 {
-- 
2.43.0