[PATCH] bluetooth: 6lowpan: fix delay work init in add_peer_chan()

[Michael Scott]

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.sc...@linaro.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