Commit 29cd718b authored Aug 27, 2013 by Gianluca Anzolin Committed by Gustavo Padovan Sep 20, 2013

Bluetooth: don't release the port in rfcomm_dev_state_change()



When the dlc is closed, rfcomm_dev_state_change() tries to release the
port in the case it cannot get a reference to the tty. However this is
racy and not even needed.

Infact as Peter Hurley points out:

1. Only consider dlcs that are 'stolen' from a connected socket, ie.
   reused. Allocated dlcs cannot have been closed prior to port
   activate and so for these dlcs a tty reference will always be avail
   in rfcomm_dev_state_change() -- except for the conditions covered by
   #2b below.
2. If a tty was at some point previously created for this rfcomm, then
   either
   (a) the tty reference is still avail, so rfcomm_dev_state_change()
       will perform a hangup. So nothing to do, or,
   (b) the tty reference is no longer avail, and the tty_port will be
       destroyed by the last tty_port_put() in rfcomm_tty_cleanup.
       Again, no action required.
3. Prior to obtaining the dlc lock in rfcomm_dev_add(),
   rfcomm_dev_state_change() will not 'see' a rfcomm_dev so nothing to
   do here.
4. After releasing the dlc lock in rfcomm_dev_add(),
   rfcomm_dev_state_change() will 'see' an incomplete rfcomm_dev if a
   tty reference could not be obtained. Again, the best thing to do here
   is nothing. Any future attempted open() will block on
   rfcomm_dev_carrier_raised(). The unconnected device will exist until
   released by ioctl(RFCOMMRELEASEDEV).

The patch removes the aforementioned code and uses the
tty_port_tty_hangup() helper to hangup the tty.

Signed-off-by: Gianluca Anzolin <gianluca@sottospazio.it>
Reviewed-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>

parent bf543036

net/bluetooth/rfcomm/tty.c

+2 −33

Original line number	Diff line number	Diff line
		@@ -569,7 +569,6 @@ static void rfcomm_dev_data_ready(struct rfcomm_dlc dlc, struct sk_buff skb)
		static void rfcomm_dev_state_change(struct rfcomm_dlc *dlc, int err)
		{
		struct rfcomm_dev *dev = dlc->owner;
		struct tty_struct *tty;
		if (!dev)
		return;

		@@ -581,38 +580,8 @@ static void rfcomm_dev_state_change(struct rfcomm_dlc *dlc, int err)
		DPM_ORDER_DEV_AFTER_PARENT);

		wake_up_interruptible(&dev->port.open_wait);
		} else if (dlc->state == BT_CLOSED) {
		tty = tty_port_tty_get(&dev->port);
		if (!tty) {
		if (test_bit(RFCOMM_RELEASE_ONHUP, &dev->flags)) {
		/* Drop DLC lock here to avoid deadlock
		* 1. rfcomm_dev_get will take rfcomm_dev_lock
		* but in rfcomm_dev_add there's lock order:
		* rfcomm_dev_lock -> dlc lock
		* 2. tty_port_put will deadlock if it's
		* the last reference
		*
		* FIXME: when we release the lock anything
		* could happen to dev, even its destruction
		*/
		rfcomm_dlc_unlock(dlc);
		if (rfcomm_dev_get(dev->id) == NULL) {
		rfcomm_dlc_lock(dlc);
		return;
		}

		if (!test_and_set_bit(RFCOMM_TTY_RELEASED,
		&dev->flags))
		tty_port_put(&dev->port);

		tty_port_put(&dev->port);
		rfcomm_dlc_lock(dlc);
		}
		} else {
		tty_hangup(tty);
		tty_kref_put(tty);
		}
		}
		} else if (dlc->state == BT_CLOSED)
		tty_port_tty_hangup(&dev->port, false);
		}

		static void rfcomm_dev_modem_status(struct rfcomm_dlc *dlc, u8 v24_sig)

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