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Date:   Wed,  9 Dec 2020 18:02:48 +0200
From:   Maxim Mikityanskiy <>
To:     "David S. Miller" <>,
        Jamal Hadi Salim <>,
        Cong Wang <>,
        Jiri Pirko <>
Cc:     Saeed Mahameed <>,
        Jakub Kicinski <>,
        Tariq Toukan <>,
        Maxim Mikityanskiy <>,, Maxim Mikityanskiy <>,
        Tariq Toukan <>
Subject: [PATCH net-next 1/4] net: sched: Add multi-queue support to sch_tree_lock

The existing qdiscs that set TCQ_F_MQROOT don't use sch_tree_lock.
However, hardware-offloaded HTB will start setting this flag while also
using sch_tree_lock.

The current implementation of sch_tree_lock basically locks on
qdisc->dev_queue->qdisc, and it works fine when the tree is attached to
some queue. However, it's not the case for MQROOT qdiscs: such a qdisc
is the root itself, and its dev_queue just points to queue 0, while not
actually being used, because there are real per-queue qdiscs.

This patch changes the logic of sch_tree_lock and sch_tree_unlock to
lock the qdisc itself if it's the MQROOT.

Signed-off-by: Maxim Mikityanskiy <>
Reviewed-by: Tariq Toukan <>
 include/net/sch_generic.h | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h
index 162ed6249e8b..cfac2b0b5cc7 100644
--- a/include/net/sch_generic.h
+++ b/include/net/sch_generic.h
@@ -563,14 +563,20 @@ static inline struct net_device *qdisc_dev(const struct Qdisc *qdisc)
 	return qdisc->dev_queue->dev;
-static inline void sch_tree_lock(const struct Qdisc *q)
+static inline void sch_tree_lock(struct Qdisc *q)
-	spin_lock_bh(qdisc_root_sleeping_lock(q));
+	if (q->flags & TCQ_F_MQROOT)
+		spin_lock_bh(qdisc_lock(q));
+	else
+		spin_lock_bh(qdisc_root_sleeping_lock(q));
-static inline void sch_tree_unlock(const struct Qdisc *q)
+static inline void sch_tree_unlock(struct Qdisc *q)
-	spin_unlock_bh(qdisc_root_sleeping_lock(q));
+	if (q->flags & TCQ_F_MQROOT)
+		spin_unlock_bh(qdisc_lock(q));
+	else
+		spin_unlock_bh(qdisc_root_sleeping_lock(q));
 extern struct Qdisc noop_qdisc;

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