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    SubjectRe: bluetooth: fix deadlock on device reset and power down
    Am 02.04.2012 08:55, schrieb Andrei Emeltchenko:
    > Hi Alexander,
    > On Sat, Mar 31, 2012 at 03:23:38PM +0200, Alexander Holler wrote:
    >> I've experienced a deadlock on shutdown using kernel 3.3 and tracked
    >> it down. Because I'm not very familiar with the bluetooth stack I'm
    >> not sure if the below patch is correct, but it fixed the problem
    >> here.
    > Could you please attach deadlock dump?
    >> Commit 09fd0de5bd8f8ef3317e5365f92f1a13dcd89aa9 introduced a deadlock:
    >> bluetoothd calls ioctl HCIDEVDOWN
    >> hci_sock_ioctl()
    >> hci_dev_close()
    >> hci_dev_do_close()
    >> hci_dev_lock(hdev);
    >> inquiry_cache_flush();
    >> hci_conn_hash_flush();
    >> hci_conn_del()
    >> cancel_delayed_work_sync()
    >> hci_conn_timeout()
    >> hci_dev_lock(hdev); /* DEADLOCK */
    > I am actually not sure that hci_conn_timeout locks hdev. Why do you think
    > so?

    By reading the source, printk and suffering through the deadlock. It's
    especially painfull when using a bt-keyboard and systemd, because
    systemd tries 4 times (~ some minutes) to kill bluetoothd before it
    marks the service as failed and finally continues to shut down.

    Just try to kill bluetoothd while a bt-mouse or bt-keyboard is connected.

    But I have to admit, that my patch is likely the wrong solution as I
    think it will introduce some race conditions. Anyway, I prefer to live
    with them (the race conditions) instead of the deadlock. So for
    inclusion into the kernel a proper solution is needed.
    But already said, I'm not familiar with the bt-stack and don't know
    about the locking strategies inside the stack, so it's hard for me to
    find my way through the source.



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