Return-Path: From: Gianluca Anzolin To: gustavo@padovan.org Cc: peter@hurleysoftware.com, marcel@holtmann.org, linux-bluetooth@vger.kernel.org, gregkh@linuxfoundation.org, jslaby@suse.cz, Gianluca Anzolin Subject: [PATCH] rfcomm: don't release the port in rfcomm_dev_state_change() Date: Tue, 27 Aug 2013 18:28:46 +0200 Message-Id: <1377620926-23370-1-git-send-email-gianluca@sottospazio.it> List-ID: 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 --- net/bluetooth/rfcomm/tty.c | 35 ++--------------------------------- 1 file changed, 2 insertions(+), 33 deletions(-) diff --git a/net/bluetooth/rfcomm/tty.c b/net/bluetooth/rfcomm/tty.c index 6d126fa..84fcf9f 100644 --- a/net/bluetooth/rfcomm/tty.c +++ b/net/bluetooth/rfcomm/tty.c @@ -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) -- 1.8.4