Patch "Bluetooth: 6lowpan: fix delay work init in add_peer_chan()" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

Bluetooth: 6lowpan: fix delay work init in add_peer_chan()

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
bluetooth-6lowpan-fix-delay-work-init-in-add_peer_chan.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Michael Scott <[email protected]>
Date: Tue, 28 Mar 2017 23:10:54 -0700
Subject: Bluetooth: 6lowpan: fix delay work init in add_peer_chan()

From: Michael Scott <[email protected]>

[ 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.

---
 net/bluetooth/6lowpan.c |   10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

@@ -755,7 +755,8 @@ static void set_ip_addr_bits(u8 addr_typ
 }
 
 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;
 

@@ -786,7 +787,8 @@ static struct l2cap_chan *add_peer_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;

@@ -843,6 +845,7 @@ out:
 static inline void chan_ready_cb(struct l2cap_chan *chan)
 {
 	struct lowpan_btle_dev *dev;
+	bool new_netdev = false;
 
 	dev = lookup_dev(chan->conn);
 

@@ -853,12 +856,13 @@ static inline void chan_ready_cb(struct
 			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);
 }
 

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/bluetooth-6lowpan-fix-delay-work-init-in-add_peer_chan.patch