My laptop has a built-in Sierra wireless device. When I flicked the switch to disable it, which effectively unplugs the USB device, I got this oops: sierra3 ttyUSB0: Sierra USB modem (3 port) converter now disconnected from ttyUSB0 PM: Removing info for usb-serial:ttyUSB0 PM: Removing info for No Bus:ttyUSB1 sierra3 ttyUSB1: Sierra USB modem (3 port) converter now disconnected from ttyUSB1 PM: Removing info for usb-serial:ttyUSB1 PM: Removing info for No Bus:ttyUSB2 sierra3 ttyUSB2: Sierra USB modem (3 port) converter now disconnected from ttyUSB2 PM: Removing info for usb-serial:ttyUSB2 BUG: unable to handle kernel NULL pointer dereference at virtual address 0000018c printing eip: f8e52cd7 *pde = 34187001 Oops: 0000 [#1] SMP Modules linked in: ppp_deflate zlib_deflate ppp_async crc_ccitt ppp_generic slhc sierra usbserial i915 drm autofs4 hidp rfcomm l2cap bluetooth xt_tcpudp iptable_filter ip_tables x_tables vfat fat video ibm_acpi p arport_pc lp parport snd_hda_intel snd_hda_codec snd_seq_dummy snd_seq_oss snd_seq_midi_event snd_seq snd_ seq_device snd_pcm_oss wlan_scan_sta snd_mixer_oss snd_pcm ath_rate_sample ath_pci mmc_block wlan sdhci sn d_timer pcspkr e1000 snd soundcore sg ohci1394 ath_hal mmc_core snd_page_alloc ieee1394 rtc_cmos rtc_core serio_raw rtc_lib rtc ehci_hcd uhci_hcd CPU: 0 EIP: 0060:[] Not tainted VLI EFLAGS: 00010246 (2.6.21-rc4 #126) EIP is at sierra_shutdown+0x3a/0x113 [sierra] eax: 00000000 ebx: 00000000 ecx: 00000000 edx: f8e52c9d esi: 00000000 edi: e889fa1c ebp: e84c0e2c esp: e84c0e0c ds: 007b es: 007b fs: 00d8 gs: 0033 ss: 0068 Process pppd (pid: 3847, ti=e84c0000 task=e8553550 task.ti=e84c0000) Stack: 00000002 e84c0e18 c01cfda8 e84c0e20 c0240431 e889fa1c 00000003 e8a79d00 e84c0e50 f8e219e4 f8e5212d 00000021 00000000 00000000 00000000 e889fa50 f8e21956 e84c0e70 c01d099a e84c0e78 f8e52c58 e84c0e6c f6c5576c f6c55760 Call Trace: [] show_trace_log_lvl+0x1a/0x2f [] show_stack_log_lvl+0x9d/0xa5 [] show_registers+0x1c2/0x293 [] die+0x122/0x224 [] do_page_fault+0x505/0x5e1 [] error_code+0x7c/0x84 [] destroy_serial+0x8e/0x124 [usbserial] [] kref_put+0x63/0x71 [] usb_serial_put+0x10/0x12 [usbserial] [] serial_close+0xb6/0xbe [usbserial] [] release_dev+0x1f0/0x5f9 [] tty_release+0x12/0x1c [] __fput+0xb8/0x162 [] fput+0x17/0x19 [] filp_close+0x54/0x5c [] sys_close+0x63/0x97 [] syscall_call+0x7/0xb ======================= Code: e5 f8 00 74 1c c7 44 24 08 97 2e e5 f8 c7 44 24 04 06 2f e5 f8 c7 04 24 22 2f e5 f8 e8 47 ff 2c c7 3 1 f6 eb 4c 8b 44 b7 14 31 db <8b> 80 8c 01 00 00 89 45 ec 8b 55 ec 8b 04 9a 85 c0 74 0b 83 78 EIP: [] sierra_shutdown+0x3a/0x113 [sierra] SS:ESP 0068:e84c0e0c This was compiled from git change 0a14fe6e5efd0af0f9c6c01e0433445d615d0110. .config attached. The hardware is a Lenovo ThinkPad X60, with the integrated Verizon Sierra wireless modem: Bus 002 Device 002: ID 1199:0218 Sierra Wireless, Inc. Thanks, J