We are using sierra modem for 4G LTE networks. we used to communicate
with modem using AT commands via ttyUSB ports.
Recently we observed a crash in usb driver interface when we try to
post some AT commands. After the crash the kernel seems to be hanged.
We were not able to execute any commands or open a new tty terminal.
Even reboot command was not working fine.
The system went to completely unusable/unstable state. It recovered
only after hard reboot.



Nov 30 18:59:01   ATCMD = [AT+CMEE=2]
Nov 30 18:59:02   [AT_TRX]Garbage cleared
Nov 30 18:59:02   [AT_TRX]Data from Stream --> [OK]
Nov 30 18:59:02   [AT_TRX]Poll Ended
Nov 30 18:59:02   [AT_TRX]Result     :[-1]

Nov 30 18:59:02   [AT_TRX]Garbage cleared
Nov 30 18:59:02  kernel: [19926.147811] usb 2-1.3: USB disconnect,
device number 126
Nov 30 18:59:02  kernel: [19926.147985] sierra ttyUSB0: Sierra USB
modem converter now disconnected from ttyUSB0
Nov 30 18:59:02  kernel: [19926.148002] sierra 2-1.3:1.0: device disconnected
Nov 30 18:59:02  kernel: [19926.148127] sierra ttyUSB1: Sierra USB
modem converter now disconnected from ttyUSB1
Nov 30 18:59:02  kernel: [19926.148138] sierra 2-1.3:1.1: device disconnected
Nov 30 18:59:02  kernel: [19926.150070] sierra ttyUSB2:
sierra_submit_rx_urbs: submit urb failed: -19
Nov 30 18:59:02  kernel: [19926.152626] sierra ttyUSB2:
sierra_submit_rx_urbs: submit urb failed: -19
Nov 30 18:59:02  kernel: [19926.155136] sierra ttyUSB2:
sierra_submit_rx_urbs: submit urb failed: -19
Nov 30 18:59:02  kernel: [19926.157589] sierra ttyUSB2:
sierra_submit_rx_urbs: submit urb failed: -19
Nov 30 18:59:02  kernel: [19926.159999] sierra ttyUSB2:
sierra_submit_rx_urbs: submit urb failed: -19
Nov 30 18:59:02  kernel: [19926.162438] sierra ttyUSB2:
sierra_submit_rx_urbs: submit urb failed: -19
Nov 30 18:59:02  kernel: [19926.164870] sierra ttyUSB2:
sierra_submit_rx_urbs: submit urb failed: -19
Nov 30 19:01:12  kernel: [20056.174514] INFO: task khubd:369 blocked
for more than 120 seconds.
Nov 30 19:01:12  kernel: [20056.176931]       Tainted: G           O
3.12.0.custom-1.3 #2
Nov 30 19:01:12  kernel: [20056.179297] "echo 0 >
/proc/sys/kernel/hung_task_timeout_secs" disables this message.
Nov 30 19:01:12  kernel: [20056.181648] khubd           D
ffff880409a3f3c8     0   369      2 0x00000000
Nov 30 19:01:12  kernel: [20056.181653]  ffff880409a3f0c0
0000000000000046 0000000000000000 ffff88040b573780
Nov 30 19:01:12  kernel: [20056.181655]  ffff880032f1ffd8
ffff880032f1ffd8 ffff880032f1ffd8 ffff880409a3f0c0
Nov 30 19:01:12  kernel: [20056.181657]  0000000080000000
ffff88035aafc9e8 ffff88035aafc9ec ffff880409a3f0c0
Nov 30 19:01:12  kernel: [20056.181660] Call Trace:
Nov 30 19:01:12  kernel: [20056.181667]  [<ffffffff814ef199>] ?
schedule_preempt_disabled+0x9/0x10
Nov 30 19:01:12  kernel: [20056.181670]  [<ffffffff814ed4f1>] ?
__mutex_lock_slowpath+0x141/0x1c0
Nov 30 19:01:12  kernel: [20056.181673]  [<ffffffff814ed586>] ?
mutex_lock+0x16/0x30
Nov 30 19:01:12  kernel: [20056.181685]  [<ffffffffa0106f4e>] ?
usb_serial_disconnect+0x2e/0x120 [usbserial]
Nov 30 19:01:12  kernel: [20056.181699]  [<ffffffffa01271aa>] ?
usb_unbind_interface+0x6a/0x1c0 [usbcore]
Nov 30 19:01:12  kernel: [20056.181705]  [<ffffffff81394be9>] ?
__device_release_driver+0x79/0xf0
Nov 30 19:01:12  kernel: [20056.181707]  [<ffffffff81393100>] ?
bus_get_device_klist+0x10/0x10
Nov 30 19:01:12  kernel: [20056.181709]  [<ffffffff81394e55>] ?
device_release_driver+0x25/0x40
Nov 30 19:01:12  kernel: [20056.181712]  [<ffffffff81394672>] ?
bus_remove_device+0xf2/0x140
Nov 30 19:01:12  kernel: [20056.181714]  [<ffffffff81391a25>] ?
device_del+0x115/0x1a0
Nov 30 19:01:12  kernel: [20056.181722]  [<ffffffffa0124e34>] ?
usb_disable_device+0x94/0x1d0 [usbcore]
Nov 30 19:01:12  kernel: [20056.181728]  [<ffffffffa011c4ee>] ?
usb_disconnect+0x8e/0x190 [usbcore]
Nov 30 19:01:12  kernel: [20056.181734]  [<ffffffffa011dc02>] ?
hub_thread+0x422/0x1380 [usbcore]
Nov 30 19:01:12  kernel: [20056.181738]  [<ffffffff814edf9e>] ?
__schedule+0x2de/0x770
Nov 30 19:01:12  kernel: [20056.181740]  [<ffffffff8107d730>] ?
finish_wait+0x90/0x90
Nov 30 19:01:12  kernel: [20056.181747]  [<ffffffffa011d7e0>] ?
hub_port_debounce+0xe0/0xe0 [usbcore]
Nov 30 19:01:12  kernel: [20056.181750]  [<ffffffff8107cfd3>] ?
kthread+0xb3/0xc0
Nov 30 19:01:12  kernel: [20056.181753]  [<ffffffff81080000>] ?
hrtimer_get_remaining+0x20/0x50
Nov 30 19:01:12  kernel: [20056.181756]  [<ffffffff8107cf20>] ?
kthread_create_on_node+0x110/0x110
Nov 30 19:01:12  kernel: [20056.181758]  [<ffffffff814f7e0c>] ?
ret_from_fork+0x7c/0xb0
Nov 30 19:01:12  kernel: [20056.181761]  [<ffffffff8107cf20>] ?
kthread_create_on_node+0x110/0x110

Regards,
Saravanan N
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