netdev - [PATCH stable] net: sch_generic: fix the missing new qdisc assignment bug

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Date:   Tue, 3 Nov 2020 11:25:38 +0800
From:   Yunsheng Lin <linyunsheng@...wei.com>
To:     <gregkh@...uxfoundation.org>, <stable@...r.kernel.org>
CC:     <vpai@...mai.com>, <Joakim.Tjernlund@...inera.com>,
        <xiyou.wangcong@...il.com>, <johunt@...mai.com>,
        <jhs@...atatu.com>, <jiri@...nulli.us>, <davem@...emloft.net>,
        <kuba@...nel.org>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linuxarm@...wei.com>,
        <john.fastabend@...il.com>, <eric.dumazet@...il.com>,
        <dsahern@...il.com>
Subject: [PATCH stable] net: sch_generic: fix the missing new qdisc assignment bug

commit 2fb541c862c9 ("net: sch_generic: aviod concurrent reset and enqueue op for lockless qdisc")

When the above upstream commit is backported to stable kernel,
one assignment is missing, which causes two problems reported
by Joakim and Vishwanath, see [1] and [2].

So add the assignment back to fix it.

1. https://www.spinics.net/lists/netdev/msg693916.html
2. https://www.spinics.net/lists/netdev/msg695131.html

Fixes: 749cc0b0c7f3 ("net: sch_generic: aviod concurrent reset and enqueue op for lockless qdisc")
Signed-off-by: Yunsheng Lin <linyunsheng@...wei.com>
---
 net/sched/sch_generic.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index 0e275e1..6e6147a 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -1127,10 +1127,13 @@ static void dev_deactivate_queue(struct net_device *dev,
 				 void *_qdisc_default)
 {
 	struct Qdisc *qdisc = rtnl_dereference(dev_queue->qdisc);
+	struct Qdisc *qdisc_default = _qdisc_default;
 
 	if (qdisc) {
 		if (!(qdisc->flags & TCQ_F_BUILTIN))
 			set_bit(__QDISC_STATE_DEACTIVATED, &qdisc->state);
+
+		rcu_assign_pointer(dev_queue->qdisc, qdisc_default);
 	}
 }
 
-- 
2.7.4