We are experiencing stuck processes (D state) which are talking to an FTD_SIO usb_serial adapter. The process sometimes has to close the serial device when it detects an error or a timeout.

We rebuilt the kernel with the CONFIG_DEBUG_USB option and the stuck processes reporting enabled.

The output was this:
=============================================================================
[89400.258190] INFO: task XXXXXX:26743 blocked for more than 120 seconds.
[89400.258263] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[89400.258329] XXXXXXXXX        D c132e6a0     0 26743 2260 0x00000000
[89400.258397] de2e5e5c 00200082 de2e5dfc c132e6a0 00000000 68d4dbc8 0000511c db24c000 [89400.258506] de2e4000 db24c000 de002c80 dee34000 c1537ea0 de2e5e38 c1315cb0 def5ac00 [89400.258614] c104a7ae de2e5e30 c12a9b48 de2e5e38 c104a7ae de2e5e64 c13169a6 c14eee71
[89400.258722] Call Trace:
[89400.258783]  [<c132e6a0>] ? start_ed_unlink+0x19/0x4f
[89400.258854]  [<c1315cb0>] ? unlink1+0x29/0x13d
[89400.258913]  [<c104a7ae>] ? sub_preempt_count+0xb/0xa5
[89400.258997]  [<c12a9b48>] ? put_device+0x14/0x16
[89400.259099]  [<c104a7ae>] ? sub_preempt_count+0xb/0xa5
[89400.259160]  [<c13169a6>] ? usb_hcd_unlink_urb+0xac/0xbe
[89400.259228]  [<c14eee71>] ? mutex_unlock+0x8/0x13
[89400.259283]  [<c104a7ae>] ? sub_preempt_count+0xb/0xa5
[89400.259341]  [<c10421c3>] ? prepare_to_wait+0x49/0x75
[89400.259405]  [<c14efdbb>] schedule+0x22/0x4c
[89400.259459]  [<c1317c2c>] usb_kill_urb+0x62/0x92
[89400.259514]  [<c10423a9>] ? finish_wait+0x71/0x71
[89400.259589]  [<dffd7fb1>] usb_serial_generic_close+0x78/0x90 [usbserial]
[89400.259660]  [<dffd601f>] serial_port_shutdown+0x1f/0x21 [usbserial]
[89400.259727]  [<c128ac5b>] tty_port_shutdown+0x46/0x66
[89400.259787]  [<c128b59e>] tty_port_close+0x20/0x3d
[89400.259851]  [<dffd668c>] serial_close+0x1d/0x20 [usbserial]
[89400.259920]  [<c1283b1b>] tty_release+0xce/0x525
[89400.260003]  [<c104a7ae>] ? sub_preempt_count+0xb/0xa5
[89400.262022]  [<c10f341d>] ? fsnotify+0xe/0x29f
[89400.262280]  [<c10f8c33>] ? timerfd_read+0x1bf/0x27c
[89400.262346]  [<c10f37f1>] ? __fsnotify_parent+0xe/0xd3
[89400.262410]  [<c10c0034>] __fput+0x8b/0x205
[89400.262468]  [<c10c0252>] ____fput+0xd/0xf
[89400.262526]  [<c103f0a1>] task_work_run+0x57/0x79
[89400.262584]  [<c10018c5>] do_notify_resume+0x5b/0x5d
[89400.262640]  [<c10be61a>] ? SyS_close+0x1b/0x42
[89400.262697]  [<c14f0e8b>] work_notifysig+0x24/0x29
[89400.262764]  [<c14f0000>] ? wait_for_completion+0x8/0x19
=============================================================================

(also on http://pastebin.com/zTy0uhMN )

I couldn't find the cause, nor a way to trigger this, except waiting for around 24 hours.

Is there anything we could look at to help?

Thank you in advance,
Matteo


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