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From:   Sasha Levin <Alexander.Levin@microsoft.com>
To:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "stable@vger.kernel.org" <stable@vger.kernel.org>
CC:     Michael Scott <michael.scott@linaro.org>,
        Marcel Holtmann <marcel@holtmann.org>,
        Sasha Levin <Alexander.Levin@microsoft.com>
Subject: [PATCH AUTOSEL for 4.9 164/219] Bluetooth: 6lowpan: fix delay work
 init in add_peer_chan()
Thread-Topic: [PATCH AUTOSEL for 4.9 164/219] Bluetooth: 6lowpan: fix delay
 work init in add_peer_chan()
Thread-Index: AQHTsz8aSGewpgldmUmM5u3GZ5VDjg==
Date:   Sat, 3 Mar 2018 22:29:32 +0000
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From: Michael Scott <michael.scott@linaro.org>

[ Upstream commit d2891c4d071d807f01cc911dc42a68f4568d65cf ]

When adding 6lowpan devices very rapidly we sometimes see a crash:
[23122.306615] CPU: 2 PID: 0 Comm: swapper/2 Not tainted 4.9.0-43-arm64 #1 =
Debian 4.9.9.linaro.43-1
[23122.315400] Hardware name: HiKey Development Board (DT)
[23122.320623] task: ffff800075443080 task.stack: ffff800075484000
[23122.326551] PC is at expire_timers+0x70/0x150
[23122.330907] LR is at run_timer_softirq+0xa0/0x1a0
[23122.335616] pc : [<ffff000008142dd8>] lr : [<ffff000008142f58>] pstate: =
600001c5

This was due to add_peer_chan() unconditionally initializing the
lowpan_btle_dev->notify_peers delayed work structure, even if the
lowpan_btle_dev passed into add_peer_chan() had previously been
initialized.

Normally, this would go unnoticed as the delayed work timer is set for
100 msec, however when calling add_peer_chan() faster than 100 msec it
clears out a previously queued delay work causing the crash above.

To fix this, let add_peer_chan() know when a new lowpan_btle_dev is passed
in so that it only performs the delay work initialization when needed.

Signed-off-by: Michael Scott <michael.scott@linaro.org>
Acked-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
---
 net/bluetooth/6lowpan.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/net/bluetooth/6lowpan.c b/net/bluetooth/6lowpan.c
index 1904a93f47d5..de7b82ece499 100644
--- a/net/bluetooth/6lowpan.c
+++ b/net/bluetooth/6lowpan.c
@@ -755,7 +755,8 @@ static void set_ip_addr_bits(u8 addr_type, u8 *addr)
 }
=20
 static struct l2cap_chan *add_peer_chan(struct l2cap_chan *chan,
-					struct lowpan_btle_dev *dev)
+					struct lowpan_btle_dev *dev,
+					bool new_netdev)
 {
 	struct lowpan_peer *peer;
=20
@@ -786,7 +787,8 @@ static struct l2cap_chan *add_peer_chan(struct l2cap_ch=
an *chan,
 	spin_unlock(&devices_lock);
=20
 	/* Notifying peers about us needs to be done without locks held */
-	INIT_DELAYED_WORK(&dev->notify_peers, do_notify_peers);
+	if (new_netdev)
+		INIT_DELAYED_WORK(&dev->notify_peers, do_notify_peers);
 	schedule_delayed_work(&dev->notify_peers, msecs_to_jiffies(100));
=20
 	return peer->chan;
@@ -843,6 +845,7 @@ out:
 static inline void chan_ready_cb(struct l2cap_chan *chan)
 {
 	struct lowpan_btle_dev *dev;
+	bool new_netdev =3D false;
=20
 	dev =3D lookup_dev(chan->conn);
=20
@@ -853,12 +856,13 @@ static inline void chan_ready_cb(struct l2cap_chan *c=
han)
 			l2cap_chan_del(chan, -ENOENT);
 			return;
 		}
+		new_netdev =3D true;
 	}
=20
 	if (!try_module_get(THIS_MODULE))
 		return;
=20
-	add_peer_chan(chan, dev);
+	add_peer_chan(chan, dev, new_netdev);
 	ifup(dev->netdev);
 }
=20
--=20
2.14.1