• Guenter Roeck's avatar
    usb: hub: Wait for connection to be reestablished after port reset · 22547c4c
    Guenter Roeck authored
    On a system with a defective USB device connected to an USB hub,
    an endless sequence of port connect events was observed. The sequence
    of events as observed is as follows:
    
    - Port reports connected event (port status=USB_PORT_STAT_CONNECTION).
    - Event handler debounces port and resets it by calling hub_port_reset().
    - hub_port_reset() calls hub_port_wait_reset() to wait for the reset
      to complete.
    - The reset completes, but USB_PORT_STAT_CONNECTION is not immediately
      set in the port status register.
    - hub_port_wait_reset() returns -ENOTCONN.
    - Port initialization sequence is aborted.
    - A few milliseconds later, the port again reports a connected event,
      and the sequence repeats.
    
    This continues either forever or, randomly, stops if the connection
    is already re-established when the port status is read. It results in
    a high rate of udev events. This in turn destabilizes userspace since
    the above sequence holds the device mutex pretty much continuously
    and prevents userspace from actually reading the device status.
    
    To prevent the problem from happening, let's wait for the connection
    to be re-established after a port reset. If the device was actually
    disconnected, the code will still return an error, but it will do so
    only after the long reset timeout.
    
    Cc: Douglas Anderson <dianders@chromium.org>
    Signed-off-by: default avatarGuenter Roeck <linux@roeck-us.net>
    Acked-by: default avatarAlan Stern <stern@rowland.harvard.edu>
    Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
    22547c4c
hub.c 165 KB