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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org,
        Leandro Dorileo <leandro.maciel.dorileo@intel.com>,
        Vladimir Oltean <olteanv@gmail.com>,
        Vinicius Costa Gomes <vinicius.gomes@intel.com>,
        "David S. Miller" <davem@davemloft.net>
Subject: [PATCH 5.2 12/94] taprio: Fix kernel panic in taprio_destroy
Date:   Sun,  8 Sep 2019 13:41:08 +0100
Message-Id: <20190908121150.784656515@linuxfoundation.org>
In-Reply-To: <20190908121150.420989666@linuxfoundation.org>
References: <20190908121150.420989666@linuxfoundation.org>
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From: Vladimir Oltean <olteanv@gmail.com>

taprio_init may fail earlier than this line:

	list_add(&q->taprio_list, &taprio_list);

i.e. due to the net device not being multi queue.

Attempting to remove q from the global taprio_list when it is not part
of it will result in a kernel panic.

Fix it by matching list_add and list_del better to one another in the
order of operations. This way we can keep the deletion unconditional
and with lower complexity - O(1).

Cc: Leandro Dorileo <leandro.maciel.dorileo@intel.com>
Fixes: 7b9eba7ba0c1 ("net/sched: taprio: fix picos_per_byte miscalculation")
Signed-off-by: Vladimir Oltean <olteanv@gmail.com>
Acked-by: Vinicius Costa Gomes <vinicius.gomes@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/sched/sch_taprio.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

--- a/net/sched/sch_taprio.c
+++ b/net/sched/sch_taprio.c
@@ -903,6 +903,10 @@ static int taprio_init(struct Qdisc *sch
 	 */
 	q->clockid = -1;
 
+	spin_lock(&taprio_list_lock);
+	list_add(&q->taprio_list, &taprio_list);
+	spin_unlock(&taprio_list_lock);
+
 	if (sch->parent != TC_H_ROOT)
 		return -EOPNOTSUPP;
 
@@ -920,10 +924,6 @@ static int taprio_init(struct Qdisc *sch
 	if (!opt)
 		return -EINVAL;
 
-	spin_lock(&taprio_list_lock);
-	list_add(&q->taprio_list, &taprio_list);
-	spin_unlock(&taprio_list_lock);
-
 	for (i = 0; i < dev->num_tx_queues; i++) {
 		struct netdev_queue *dev_queue;
 		struct Qdisc *qdisc;