Linux: Kernel panic after unplugging touch device

$ dmesg
...
[ 1375.352570] usbcore: deregistering interface driver nwfermi
[ 1375.352740] BUG: unable to handle kernel NULL pointer dereference at 00000054
[ 1375.352750] IP: [] mutex_lock+0xd/0x24
[ 1375.352765] *pde = 00000000
[ 1375.352770] Oops: 0002 [#1] SMP
[ 1375.352775] last sysfs file: /sys/devices/virtual/vtconsole/vtcon0/uevent
[ 1375.352782] Modules linked in: fuse loop snd_hda_codec_realtek snd_hda_codec_atihdmi snd_hda_intel snd_hda_codec snd_hwdep snd_pcm snd_seq snd_timer snd_seq_device snd usbhid joydev psmouse i2c_piix4 evdev hid nw_fermi(-) serio_raw pcfglrx(P) snd_page_alloc button ext3 jbd mbcache sd_mod crc_t10dif ata_generic ohci_hcd ahci pata_atiixp thermal thermal_sys r8169 mii ehci_hcd libata usbcore nls_base scsi_mod [last unloaded: scsi_wait_scan]
[ 1375.352834]
[ 1375.352842] Pid: 1959, comm: rmmod Tainted: P (2.6.32-5-686 #1) To be filled by O.E.M.
[ 1375.352847] EIP: 0060:[] EFLAGS: 00010246 CPU: 1
[ 1375.352851] EIP is at mutex_lock+0xd/0x24
[ 1375.352855] EAX: 00000054 EBX: 00000054 ECX: f7cd3ce0 EDX: f6604000
[ 1375.352859] ESI: 00000054 EDI: f6f7bc00 EBP: f6f7bc1c ESP: f6605ed8
[ 1375.352864] DS: 007b ES: 007b FS: 00d8 GS: 00e0 SS: 0068
[ 1375.352869] Process rmmod (pid: 1959, ti=f6604000 task=f5d2a640 task.ti=f6604000)
[ 1375.352872] Stack:
[ 1375.352875] 00000000 00000000 f857e57d ffffffff f6f7bc00 f6f7bc1c f655c800 f857ed64
[ 1375.352884] f7cc7c30 00000000 f6f7bc1c f857ed98 f857ed98 00000880 c11b326c f6f7bc1c
[ 1375.352893] f6f7bc50 c11b3308 f857ed98 00000000 f7cd3420 c11b28b2 f857ed64 f857ed90
[ 1375.352904] Call Trace:
[ 1375.352916] [] ? fermi_disconnect+0x3a/0x88 [nw_fermi]
[ 1375.352933] [] ? usb_unbind_interface+0x3f/0xb4 [usbcore]
[ 1375.352943] [] ? __device_release_driver+0x74/0xb7
[ 1375.352948] [] ? driver_detach+0x59/0x77
[ 1375.352956] [] ? bus_remove_driver+0x66/0x8e
[ 1375.352969] [] ? usb_deregister+0x76/0x7e [usbcore]
[ 1375.352977] [] ? sys_delete_module+0x19f/0x20f
[ 1375.352986] [] ? remove_vma+0x43/0x48
[ 1375.352993] [] ? do_page_fault+0x2f1/0x307
[ 1375.353001] [] ? syscall_call+0x7/0xb
[ 1375.353005] Code: c1 03 48 79 0b 89 d8 e8 ab ff ff ff 85 c0 75 0c 89 e0 25 00 e0 ff ff 89 43 10 31 c0 5b c3 53 89 c3 83 ec 04 e8 fc f8 ff ff 89 d8 ff 08 79 05 e8 60 ff ff ff 89 e0 25 00 e0 ff ff 89 43 10 5b
[ 1375.353054] EIP: [] mutex_lock+0xd/0x24 SS:ESP 0068:f6605ed8
[ 1375.353061] CR2: 0000000000000054

--- nw-fermi.c.orig        2011-07-22 00:00:00.000000000 +0200
+++ nw-fermi.c        2012-03-02 08:18:17.000000000 +0100
@@ -523,8 +523,25 @@
    int retval = 0;

    if (urb->status) {
-       err("Error on read completion routine.");
-       retval = -EFAULT;
+       dbg("URB Status: %d\n", urb->status);
+       switch(urb->status) {
+       /* device gone, unplugged or unlinked */
+       case -ECONNRESET:
+       case -ENODEV:
+       case -ENOENT:
+       case -ESHUTDOWN:
+           retval = -ENODEV;
+           break;
+       /* errors that might occur during unplugging */
+       case -EILSEQ:
+       case -EPROTO:
+       case -ETIME:
+           retval = -EIO;
+           break;
+       default:
+           err("Error on read completion routine. Code: %d", urb->status);
+           retval = -EFAULT;
+       }
    }
    else {
        if (!dev->interface) {      /* disconnect() was called */
@@ -734,6 +751,11 @@
    struct usb_fermi *dev;
    int minor = interface->minor;

+   /* the minor number should be equal to or greater than 0 */
+   if(minor < 0) {
+       return;
+   }
+
    dev = usb_get_intfdata(interface);
    usb_set_intfdata(interface, NULL);