dmesg

 r7:00000006 r6:c7ad41e0 r5:c8089840 r4:00000016
[<c04b5148>] (sys_close+0x0/0xb4) from [<c02d9760>] (ret_fast_syscall+0x0/0x2c)
 r7:00000006 r6:00000016 r5:beaa7868 r4:007a1a60
---[ end trace 029aefc14cc1dd53 ]---
------------[ cut here ]------------
WARNING: at drivers/usb/serial/usb-serial.c:447 serial_unthrottle+0x48/0x7c [usbserial]()
Modules linked in: ftdi_sio usbserial bsd_comp pppoe pppox ppp_deflate ppp_async ppp_synctty ecb ppp_mppe ppp_generic slhc tntfs(P) ntfs
Backtrace:
[<c0417588>] (dump_backtrace+0x0/0x114) from [<c02e7cf4>] (dump_stack+0x18/0x1c)
 r7:00000000 r6:bf0ca2cc r5:bf0cd9c1 r4:000001bf
[<c02e7cdc>] (dump_stack+0x0/0x1c) from [<c04681d8>] (warn_slowpath_common+0x50/0x68)
[<c0468188>] (warn_slowpath_common+0x0/0x68) from [<c0468208>] (warn_slowpath_null+0x18/0x1c)
 r7:c224b604 r6:c583d400 r5:c583d400 r4:c224b600
[<c04681f0>] (warn_slowpath_null+0x0/0x1c) from [<bf0ca2cc>] (serial_unthrottle+0x48/0x7c [usbserial])
[<c06de0b8>] (tty_unthrottle+0x0/0x64) from [<c06dc4c4>] (check_unthrottle+0x1c/0x20)
 r5:c583d78c r4:00000000
[<c06dc4a8>] (check_unthrottle+0x0/0x20) from [<c06dcba8>] (reset_buffer_flags+0x8c/0x90)
[<c06dcb1c>] (reset_buffer_flags+0x0/0x90) from [<c06dcbc0>] (n_tty_flush_buffer+0x14/0x64)
 r7:c224b604 r6:c224b604 r5:c583d400 r4:c583d400
[<c06dcbac>] (n_tty_flush_buffer+0x0/0x64) from [<c06dfa28>] (tty_ldisc_flush+0x34/0x48)
 r5:c583d400 r4:c0253cc0
[<c06df9f4>] (tty_ldisc_flush+0x0/0x48) from [<c06e024c>] (tty_port_close_end+0x1c/0xb8)
 r5:c583d400 r4:c583d400
[<c06e0230>] (tty_port_close_end+0x0/0xb8) from [<bf0ca6f4>] (serial_close+0x74/0x94 [usbserial])
 r7:c224b604 r6:c81d4860 r5:c224b600 r4:c583d400
[<c06da784>] (tty_release_dev+0x0/0x444) from [<c06dabdc>] (tty_release+0x14/0x1c)
[<c06dabc8>] (tty_release+0x0/0x1c) from [<c04b88ac>] (__fput+0x110/0x1c8)
[<c04b879c>] (__fput+0x0/0x1c8) from [<c04b8998>] (fput+0x34/0x38)
[<c04b8964>] (fput+0x0/0x38) from [<c04b513c>] (filp_close+0x78/0x84)
[<c04b50c4>] (filp_close+0x0/0x84) from [<c04b51c8>] (sys_close+0x80/0xb4)
 r7:00000006 r6:c81d4860 r5:c801c2c0 r4:00000015
[<c04b5148>] (sys_close+0x0/0xb4) from [<c02d9760>] (ret_fast_syscall+0x0/0x2c)
 r7:00000006 r6:00000015 r5:bef13868 r4:007b3ff8
---[ end trace 029aefc14cc1dd54 ]---
In usb_disconnect, and number is 1 .....
usb 1-1.3: USB disconnect, address 7
ftdi_sio ttyUSB0: ftdi_submit_read_urb - failed submitting read urb, error -19
ftdi_sio ttyUSB0: FTDI USB Serial Device converter now disconnected from ttyUSB0
ftdi_sio 1-1.3:1.0: device disconnected
usb 1-1.3: new full speed USB device using ehci_marvell and address 8
In hub_port_init, usb_device_id = 7, devnum = 8
In hub_port_init, and number is 2, retry 0, port 3 .....
usb 1-1.3: configuration #1 chosen from 1 choice
ftdi_sio 1-1.3:1.0: FTDI USB Serial Device converter detected
usb 1-1.3: Detected FT232RL
usb 1-1.3: Number of endpoints 2
usb 1-1.3: Endpoint 1 MaxPacketSize 64
usb 1-1.3: Endpoint 2 MaxPacketSize 64
usb 1-1.3: Setting MaxPacketSize 64
usb 1-1.3: FTDI USB Serial Device converter now attached to ttyUSB0