Re: [Bugme-new] [Bug 9046] New: USB Serial not sending uevent on device disconnect if port open

On Thu, 20 Sep 2007 14:05:59 -0700 (PDT)
[email protected] wrote:

> http://bugzilla.kernel.org/show_bug.cgi?id=9046
> 
>            Summary: USB Serial not sending uevent on device disconnect if
>                     port open
>            Product: Drivers
>            Version: 2.5
>      KernelVersion: 2.6.20.15 and 2.6.19.2
>           Platform: All
>         OS/Version: Linux
>               Tree: Mainline
>             Status: NEW
>           Severity: normal
>           Priority: P1
>          Component: USB
>         AssignedTo: [email protected]
>         ReportedBy: [email protected]
> 
> 
> Most recent kernel where this bug did not occur: still seen
> Distribution: KUbuntu 2.6.20.15 and Freescale BSP 2.6.19.2
> Hardware Environment: Dell Optiplex x86 and Freescale ARM Development Board
> Software Environment: Vmware running Kubuntu on Windows XP and Embedded ARM
> development board
> Problem Description:
> If you have a program that opens a port using usb-serial and the USB device is
> disconnected there is no uevent indicating the ACTION "remove" for the tty
> device (e.g ttyUSB0).  Once the port is closed the uevent is triggered and
> notifies the system the device has disconnected.  When using the port there is
> no way to get notified that the device has disconnected.  If no ports are open
> the uevent is sent without problems.  I admit this could be a design decision
> but it seems like a limitation.  I've seen the same problem in the cdc-acm
> driver.
> 
> I've debugged the problem and found a potential solution.  When the
> serial->kref is initialized it starts as one.  When the port is opened it
> obviously gets incremented.  The problem is that on the serial_disconnect there
> should be a kref_put for each port that calls tty_hangup.  Also the
> port->tty->driver_data MUST be reset to NULL otherwise when the program closes
> its open port it will crash the driver.
> 
> The proposed change is as follows:
>     if (serial) {
>                 for (i = 0; i < serial->num_ports; ++i) {
>                         port = serial->port[i];
>                         if (port && port->tty)
>             {
>                 tty_hangup(port->tty);
> 
> +                /* prevents a close from an open device crashing the driver */
> +               port->tty->driver_data = NULL; 
> +
> +               /* we are also done with the reference used by tty */
> +              usb_serial_put(serial);
>             }
>                 }
>                 /* let the last holder of this object 
>                  * cause it to be cleaned up */
>                 usb_serial_put(serial);
>         }
> Steps to reproduce:
> 1. Connect usb-serial device
> 2. Open the port (e.g. ttyUSB0) using some program (e.g. minicom)
> 3. Disconnect the usb-serial device
> 4. problem occurs here, no uevent for the remove of ttyUSB0.  /dev/ttyUSB0 is
> still around.
> 5. Can now kill/terminate the program that had the port open and the uevent
> will be sent out.
> 

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