linux-kernel - [PATCH 4.19 100/101] net: sch_generic: fix the missing new qdisc assignment bug

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Date:   Tue, 17 Nov 2020 14:06:07 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Yunsheng Lin <linyunsheng@...wei.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Brian Norris <briannorris@...omium.org>
Subject: [PATCH 4.19 100/101] net: sch_generic: fix the missing new qdisc assignment bug


When commit 2fb541c862c9 ("net: sch_generic: aviod concurrent reset and
enqueue op for lockless qdisc") 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>
Acked-by: Jakub Kicinski <kuba@...nel.org>
Tested-by: Brian Norris <briannorris@...omium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 net/sched/sch_generic.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -1116,10 +1116,13 @@ static void dev_deactivate_queue(struct
 				 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);
 	}
 }