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    Subject[PATCH AUTOSEL for 4.9 164/219] Bluetooth: 6lowpan: fix delay work init in add_peer_chan()
    Date
    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)
    }

    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(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;
    @@ -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 *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);
    }

    --
    2.14.1
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