Re: [2.4] "Fix" introduced in 2.4.27pre2 for bluetooth hci_usb race causes kernel hang

From: Marcel Holtmann (marcel_at_holtmann.org)
Date: 04/09/05

  • Next message: Alexander Nyberg: "Re: 2.6.12-rc2-mm2" 
    To: Tomas Qgren?= <stric@acc.umu.se>
Date:	Sat, 09 Apr 2005 15:39:15 +0200

    Hi Tomas,

    > I have noticed a problem with a race condition fix introduced in
    > 2.4.27-pre2 that causes the kernel to hang when disconnecting a
    > Bluetooth USB dongle or doing 'hciconfig hci0 down'. No message is
    > printed, the kernel just doesn't respond anymore.
    >
    > Seen in Changelog:
    > Marcel Holtmann:
    > o [Bluetooth] Fix race in RX complete routine of the USB drivers
    >
    > Reversing the following patch to hci_usb_rx_complete() makes 2.4.27-pre2
    > up until 2.4.30 happy and does not hang when removing the dongle
    > anymore. (bfusb.c has the same patch applied)
    >
    > 2.6.11.7 does not show the same problem, but has similar code to the
    > "fixed" (that hangs) code in 2.4, so the real problem is probably
    > somewhere else.

    does the attached patch makes any difference?

    Regards

    Marcel

    ===== drivers/bluetooth/hci_usb.c 1.23 vs edited =====
    --- 1.23/drivers/bluetooth/hci_usb.c 2004-07-31 13:02:43 +02:00
    +++ edited/drivers/bluetooth/hci_usb.c 2005-04-09 15:37:12 +02:00
    @@ -398,12 +398,12 @@
     
             BT_DBG("%s", hdev->name);
     
    + /* Synchronize with completion handlers */
             write_lock_irqsave(&husb->completion_lock, flags);
    -
    + write_unlock_irqrestore(&husb->completion_lock, flags);
    +
             hci_usb_unlink_urbs(husb);
             hci_usb_flush(hdev);
    -
    - write_unlock_irqrestore(&husb->completion_lock, flags);
     
             MOD_DEC_USE_COUNT;
             return 0;

    -
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