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Date:   Wed,  9 Dec 2020 18:02:48 +0200
From:   Maxim Mikityanskiy <maximmi@...lanox.com>
To:     "David S. Miller" <davem@...emloft.net>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Jiri Pirko <jiri@...nulli.us>
Cc:     Saeed Mahameed <saeedm@...dia.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Tariq Toukan <tariqt@...lanox.com>,
        Maxim Mikityanskiy <maximmi@...dia.com>,
        netdev@...r.kernel.org, Maxim Mikityanskiy <maximmi@...lanox.com>,
        Tariq Toukan <tariqt@...dia.com>
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 <maximmi@...lanox.com>
Reviewed-by: Tariq Toukan <tariqt@...dia.com>
---
 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;
-- 
2.20.1

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