BUG: unable to handle kernel NULL pointer dereference at 0000000000000038
IP: [<ffffffffa0e760a2>] serial_do_free+0x42/0x90 [usbserial]
PGD 4650f067 PUD 7c430067 PMD 0 
Oops: 0000 [#1] SMP 
last sysfs file: /sys/devices/LNXSYSTM:00/device:00/PNP0C0A:00/power_supply/BAT0/charge_full
CPU 0 
Modules linked in: ppp_deflate zlib_deflate bsd_comp ppp_async crc_ccitt option usbserial usb_storage binfmt_misc ppdev vboxnetadp vboxnetflt vboxdrv snd_hda_codec_idt snd_hda_intel snd_hda_codec snd_pcm_oss snd_mixer_oss snd_pcm snd_seq_dummy snd_seq_oss snd_seq_midi arc4 snd_rawmidi ecb snd_seq_midi_event iwl3945 iwlcore snd_seq snd_timer joydev snd_seq_device mac80211 pcmcia iptable_filter yenta_socket coretemp snd led_class ip_tables rsrc_nonstatic x_tables soundcore dell_wmi pcmcia_core lp psmouse parport dell_laptop dcdbas serio_raw cfg80211 nvidia(P) snd_page_alloc sha256_generic aes_x86_64 aes_generic cbc dm_crypt tg3 video output intel_agp
Pid: 2503, comm: pppd Tainted: P           2.6.31-11-generic #36-Ubuntu Latitude D620                   
RIP: 0010:[<ffffffffa0e760a2>]  [<ffffffffa0e760a2>] serial_do_free+0x42/0x90 [usbserial]
RSP: 0018:ffff88004d44fd58  EFLAGS: 00010286
RAX: 0000000000000000 RBX: ffff88006e978000 RCX: ffff8800465ea000
RDX: 0000000000000000 RSI: ffff88006a06e180 RDI: ffff88007c1a0d90
RBP: ffff88004d44fd78 R08: ffff88005a233c60 R09: 0000000000000000
R10: 00007ffffdb9bd20 R11: 0000000000000246 R12: ffff88006e978068
R13: ffff88006a06e180 R14: 0000000000000000 R15: ffff88007b7dce00
FS:  00007fb935bf96f0(0000) GS:ffff8800019cb000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
CR2: 0000000000000038 CR3: 0000000046511000 CR4: 00000000000006b0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Process pppd (pid: 2503, threadinfo ffff88004d44e000, task ffff8800464896b0)
Stack:
 ffff8800465ea000 ffff88007c1a0c00 ffff8800465ea000 ffff88006a06e180
<0> ffff88004d44fda8 ffffffffa0e76185 ffff8800465ea000 0000000000000000
<0> ffff88006a06e180 ffff88006e817910 ffff88004d44fe98 ffffffff812eecf9
Call Trace:
 [<ffffffffa0e76185>] serial_close+0x95/0xc0 [usbserial]
 [<ffffffff812eecf9>] tty_release_dev+0x159/0x5f0
 [<ffffffff81032419>] ? default_spin_lock_flags+0x9/0x10
 [<ffffffff815234ca>] ? _spin_lock_irqsave+0x2a/0x40
 [<ffffffff8107734c>] ? lock_hrtimer_base+0x2c/0x60
 [<ffffffff8107740d>] ? hrtimer_try_to_cancel+0x3d/0x90
 [<ffffffff8107747a>] ? hrtimer_cancel+0x1a/0x30
 [<ffffffff812ef1a9>] tty_release+0x19/0x30
 [<ffffffff8111b750>] __fput+0xf0/0x210
 [<ffffffff8111b88d>] fput+0x1d/0x30
 [<ffffffff81117b08>] filp_close+0x58/0x90
 [<ffffffff81117bf9>] sys_close+0xb9/0x110
 [<ffffffff81011fc2>] system_call_fastpath+0x16/0x1b
Code: 01 00 00 00 74 13 48 8b 5d e8 4c 8b 65 f0 4c 8b 6d f8 c9 c3 0f 1f 44 00 00 48 8b 1f 48 81 c7 90 01 00 00 48 8b 43 08 4c 8d 63 68 <4c> 8b 68 38 e8 45 1f 4a e0 4c 89 e7 e8 2d c0 6a e0 f6 43 18 01 
RIP  [<ffffffffa0e760a2>] serial_do_free+0x42/0x90 [usbserial]
 RSP <ffff88004d44fd58>
CR2: 0000000000000038
---[ end trace 27519a0d04114804 ]---