netdev - [PATCH] bluetooth: 6lowpan: fix delay work init in add_peer

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Date:   Tue, 28 Mar 2017 23:10:54 -0700
From:   Michael Scott <michael.scott@...aro.org>
To:     Marcel Holtmann <marcel@...tmann.org>,
        Gustavo Padovan <gustavo@...ovan.org>,
        Johan Hedberg <johan.hedberg@...il.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Jukka Rissanen <jukka.rissanen@...ux.intel.com>,
        linux-bluetooth@...r.kernel.org, linux-wpan@...r.kernel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Michael Scott <michael.scott@...aro.org>
Subject: [PATCH] bluetooth: 6lowpan: fix delay work init in add_peer_chan()

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@...aro.org>
---
 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 e27be3ca0a0c..c282482edc2c 100644
--- a/net/bluetooth/6lowpan.c
+++ b/net/bluetooth/6lowpan.c
@@ -754,7 +754,8 @@ static void set_ip_addr_bits(u8 addr_type, u8 *addr)
 }
 
 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;
 
@@ -785,7 +786,8 @@ static struct l2cap_chan *add_peer_chan(struct l2cap_chan *chan,
 	spin_unlock(&devices_lock);
 
 	/* 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));
 
 	return peer->chan;
@@ -842,6 +844,7 @@ static int setup_netdev(struct l2cap_chan *chan, struct lowpan_btle_dev **dev)
 static inline void chan_ready_cb(struct l2cap_chan *chan)
 {
 	struct lowpan_btle_dev *dev;
+	bool new_netdev = false;
 
 	dev = lookup_dev(chan->conn);
 
@@ -852,12 +855,13 @@ static inline void chan_ready_cb(struct l2cap_chan *chan)
 			l2cap_chan_del(chan, -ENOENT);
 			return;
 		}
+		new_netdev = true;
 	}
 
 	if (!try_module_get(THIS_MODULE))
 		return;
 
-	add_peer_chan(chan, dev);
+	add_peer_chan(chan, dev, new_netdev);
 	ifup(dev->netdev);
 }
 
-- 
2.11.0