I have the same problem with a Dell PowerEdge R210 II, with Dell DRAC under Ubuntu Server 14.04 LTS and 3.13 kernel: Process khubd will block in state D too.
=> need to do a hard reboot

Screenshot of htop: https://lafibre.info/serveur-linux/load-average/msg372058/#msg372058

The "dmesg" data corresponding ;

[11273834.551052] type=1400 audit(1473524094.532:28): apparmor="STATUS" operation="profile_replace" profile="unconfined" name="/sbin/dhclient" pid=22297 comm="apparmor_parser"
[11273834.551236] type=1400 audit(1473524094.532:29): apparmor="STATUS" operation="profile_replace" profile="unconfined" name="/usr/lib/NetworkManager/nm-dhcp-client.action" pid=22297 comm="apparmor_parser"
[11273834.551388] type=1400 audit(1473524094.532:30): apparmor="STATUS" operation="profile_replace" profile="unconfined" name="/usr/lib/connman/scripts/dhclient-script" pid=22297 comm="apparmor_parser"
[11359185.861753] usb 1-1.1: reset full-speed USB device number 3 using ehci-pci
[11359190.938076] usb 1-1.1: device descriptor read/64, error -32
[11359191.114227] usb 1-1.1: device descriptor read/64, error -32
[11359191.290375] usb 1-1.1: reset full-speed USB device number 3 using ehci-pci
[11359191.362427] usb 1-1.1: device descriptor read/64, error -32
[11359191.538586] usb 1-1.1: device descriptor read/64, error -32
[11359191.714748] usb 1-1.1: reset full-speed USB device number 3 using ehci-pci
[11359192.123084] usb 1-1.1: device not accepting address 3, error -32
[11359192.195140] usb 1-1.1: reset full-speed USB device number 3 using ehci-pci
[11359192.603502] usb 1-1.1: device not accepting address 3, error -32
[11359192.604316] usb 1-1.1: USB disconnect, device number 3
[11359384.590873] INFO: task khubd:71 blocked for more than 120 seconds.
[11359384.591241]       Not tainted 3.13.0-85-generic #129-Ubuntu
[11359384.591574] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[11359384.592047] khubd           D ffff88043fc93180     0    71      2 0x00000000
[11359384.592052]  ffff880428cd7c80 0000000000000046 ffff8804293d6000 ffff880428cd7fd8
[11359384.592057]  0000000000013180 0000000000013180 ffff8804293d6000 ffff880428c290e8
[11359384.592061]  ffff880428c290ec ffff8804293d6000 00000000ffffffff ffff880428c290f0
[11359384.592065] Call Trace:
[11359384.592074]  [<ffffffff81730089>] schedule_preempt_disabled+0x29/0x70
[11359384.592078]  [<ffffffff81731ef5>] __mutex_lock_slowpath+0x135/0x1b0
[11359384.592082]  [<ffffffff81731f8f>] mutex_lock+0x1f/0x2f
[11359384.592088]  [<ffffffff81545c04>] usb_disconnect+0x64/0x200
[11359384.592091]  [<ffffffff815487d3>] hub_port_connect_change+0xd3/0xb20
[11359384.592096]  [<ffffffff8154333d>] ? hub_port_status+0xdd/0x120
[11359384.592099]  [<ffffffff815496f4>] hub_events+0x4d4/0xa20
[11359384.592102]  [<ffffffff81549c75>] hub_thread+0x35/0x160
[11359384.592106]  [<ffffffff810add60>] ? prepare_to_wait_event+0x100/0x100
[11359384.592109]  [<ffffffff81549c40>] ? hub_events+0xa20/0xa20
[11359384.592113]  [<ffffffff8108deb2>] kthread+0xd2/0xf0
[11359384.592117]  [<ffffffff8108dde0>] ? kthread_create_on_node+0x1c0/0x1c0
[11359384.592121]  [<ffffffff8173c2e8>] ret_from_fork+0x58/0x90
[11359384.592125]  [<ffffffff8108dde0>] ? kthread_create_on_node+0x1c0/0x1c0
[11359384.592133] INFO: task kworker/4:2:18579 blocked for more than 120 seconds.
[11359384.592544]       Not tainted 3.13.0-85-generic #129-Ubuntu
[11359384.592869] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[11359384.593321] kworker/4:2     D ffff88043fd13180     0 18579      2 0x00000000
[11359384.593336] Workqueue: events hid_reset [usbhid]
[11359384.593338]  ffff8803f27af850 0000000000000046 ffff8800badb9800 ffff8803f27affd8
[11359384.593341]  0000000000013180 0000000000013180 ffff8800badb9800 ffff8803f27af998
[11359384.593345]  ffff8803f27af9a0 7fffffffffffffff ffff8800badb9800 ffff8800badb9800
[11359384.593348] Call Trace:
[11359384.593352]  [<ffffffff8172fb69>] schedule+0x29/0x70
[11359384.593355]  [<ffffffff8172ed89>] schedule_timeout+0x279/0x320
[11359384.593359]  [<ffffffff810a1988>] ? __enqueue_entity+0x78/0x80
[11359384.593364]  [<ffffffff810a7dbd>] ? enqueue_entity+0x2ad/0xc00
[11359384.593367]  [<ffffffff81730686>] wait_for_completion+0xa6/0x160
[11359384.593372]  [<ffffffff8109d570>] ? wake_up_state+0x20/0x20
[11359384.593377]  [<ffffffff8108748d>] flush_work+0xed/0x1b0
[11359384.593381]  [<ffffffff810836a0>] ? wake_up_worker+0x30/0x30
[11359384.593385]  [<ffffffff81087652>] __cancel_work_timer+0x92/0x1a0
[11359384.593390]  [<ffffffff81076cfb>] ? lock_timer_base.isra.35+0x2b/0x50
[11359384.593394]  [<ffffffff81087770>] cancel_work_sync+0x10/0x20
[11359384.593400]  [<ffffffffa00265dc>] usbhid_close+0xbc/0x100 [usbhid]
[11359384.593407]  [<ffffffffa00771e2>] hidinput_close+0x22/0x30 [hid]
[11359384.593412]  [<ffffffff8159287a>] input_close_device+0x4a/0x70
[11359384.593417]  [<ffffffff815986ff>] evdev_cleanup+0xbf/0xd0
[11359384.593421]  [<ffffffff8159873b>] evdev_disconnect+0x2b/0x60
[11359384.593425]  [<ffffffff81594e85>] __input_unregister_device+0xc5/0x1b0
[11359384.593429]  [<ffffffff8159501d>] input_unregister_device+0x4d/0x80
[11359384.593436]  [<ffffffffa0077386>] hidinput_disconnect+0x96/0xc0 [hid]
[11359384.593442]  [<ffffffffa0073e70>] hid_disconnect+0x60/0x70 [hid]
[11359384.593447]  [<ffffffffa0073f3d>] hid_device_remove+0xbd/0xd0 [hid]
[11359384.593453]  [<ffffffff8149f08f>] __device_release_driver+0x7f/0xf0
[11359384.593457]  [<ffffffff8149f123>] device_release_driver+0x23/0x30
[11359384.593461]  [<ffffffff8149e9a8>] bus_remove_device+0x108/0x180
[11359384.593464]  [<ffffffff8149b439>] device_del+0x129/0x1c0
[11359384.593470]  [<ffffffffa0073fd7>] hid_destroy_device+0x27/0x60 [hid]
[11359384.593475]  [<ffffffffa00245a7>] usbhid_disconnect+0x27/0x50 [usbhid]
[11359384.593480]  [<ffffffff81553814>] usb_unbind_interface+0x64/0x1c0
[11359384.593484]  [<ffffffff8149f08f>] __device_release_driver+0x7f/0xf0
[11359384.593487]  [<ffffffff8149f123>] device_release_driver+0x23/0x30
[11359384.593492]  [<ffffffff815539f8>] usb_driver_release_interface+0x88/0x90
[11359384.593496]  [<ffffffff81553a2e>] usb_forced_unbind_intf+0x2e/0x60
[11359384.593500]  [<ffffffff81553ab9>] unbind_marked_interfaces.isra.9+0x59/0x70
[11359384.593504]  [<ffffffff81553bf9>] usb_unbind_and_rebind_marked_interfaces+0x19/0x30
[11359384.593507]  [<ffffffff81548680>] usb_reset_device+0x140/0x1c0
[11359384.593513]  [<ffffffffa0024bdf>] hid_reset+0x15f/0x1d0 [usbhid]
[11359384.593517]  [<ffffffff81086298>] process_one_work+0x178/0x470
[11359384.593521]  [<ffffffff810870b1>] worker_thread+0x121/0x410
[11359384.593525]  [<ffffffff81086f90>] ? rescuer_thread+0x430/0x430
[11359384.593528]  [<ffffffff8108deb2>] kthread+0xd2/0xf0
[11359384.593532]  [<ffffffff8108dde0>] ? kthread_create_on_node+0x1c0/0x1c0
[11359384.593535]  [<ffffffff8173c2e8>] ret_from_fork+0x58/0x90
[11359384.593539]  [<ffffffff8108dde0>] ? kthread_create_on_node+0x1c0/0x1c0
[11359504.693037] INFO: task khubd:71 blocked for more than 120 seconds.
[11359504.693457]       Not tainted 3.13.0-85-generic #129-Ubuntu
[11359504.693849] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[11359504.694397] khubd           D ffff88043fc93180     0    71      2 0x00000000
[11359504.694402]  ffff880428cd7c80 0000000000000046 ffff8804293d6000 ffff880428cd7fd8
[11359504.694407]  0000000000013180 0000000000013180 ffff8804293d6000 ffff880428c290e8
[11359504.694411]  ffff880428c290ec ffff8804293d6000 00000000ffffffff ffff880428c290f0
[11359504.694415] Call Trace:
[11359504.694424]  [<ffffffff81730089>] schedule_preempt_disabled+0x29/0x70
[11359504.694428]  [<ffffffff81731ef5>] __mutex_lock_slowpath+0x135/0x1b0
[11359504.694432]  [<ffffffff81731f8f>] mutex_lock+0x1f/0x2f
[11359504.694438]  [<ffffffff81545c04>] usb_disconnect+0x64/0x200
[11359504.694441]  [<ffffffff815487d3>] hub_port_connect_change+0xd3/0xb20
[11359504.694446]  [<ffffffff8154333d>] ? hub_port_status+0xdd/0x120
[11359504.694449]  [<ffffffff815496f4>] hub_events+0x4d4/0xa20
[11359504.694452]  [<ffffffff81549c75>] hub_thread+0x35/0x160
[11359504.694456]  [<ffffffff810add60>] ? prepare_to_wait_event+0x100/0x100
[11359504.694459]  [<ffffffff81549c40>] ? hub_events+0xa20/0xa20
[11359504.694463]  [<ffffffff8108deb2>] kthread+0xd2/0xf0
[11359504.694467]  [<ffffffff8108dde0>] ? kthread_create_on_node+0x1c0/0x1c0
[11359504.694471]  [<ffffffff8173c2e8>] ret_from_fork+0x58/0x90
[11359504.694475]  [<ffffffff8108dde0>] ? kthread_create_on_node+0x1c0/0x1c0
[11359504.694484] INFO: task kworker/4:2:18579 blocked for more than 120 seconds.
[11359504.694964]       Not tainted 3.13.0-85-generic #129-Ubuntu
[11359504.695349] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[11359504.712710] kworker/4:2     D ffff88043fd13180     0 18579      2 0x00000000
[11359504.712725] Workqueue: events hid_reset [usbhid]
[11359504.712727]  ffff8803f27af850 0000000000000046 ffff8800badb9800 ffff8803f27affd8
[11359504.712730]  0000000000013180 0000000000013180 ffff8800badb9800 ffff8803f27af998
[11359504.712747]  ffff8803f27af9a0 7fffffffffffffff ffff8800badb9800 ffff8800badb9800
[11359504.712772] Call Trace:
...
[11359624.815201] INFO: task khubd:71 blocked for more than 120 seconds.
[11359624.824377]       Not tainted 3.13.0-85-generic #129-Ubuntu
[11359624.833588] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[11359624.852395] khubd           D ffff88043fc93180     0    71      2 0x00000000
[11359624.852398]  ffff880428cd7c80 0000000000000046 ffff8804293d6000 ffff880428cd7fd8
[11359624.852401]  0000000000013180 0000000000013180 ffff8804293d6000 ffff880428c290e8
[11359624.852402]  ffff880428c290ec ffff8804293d6000 00000000ffffffff ffff880428c290f0
[11359624.852412] Call Trace:
...
[11359624.852460] INFO: task kworker/4:2:18579 blocked for more than 120 seconds.
[11359624.871561]       Not tainted 3.13.0-85-generic #129-Ubuntu
[11359624.881830] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[11359624.902645] kworker/4:2     D ffff88043fd13180     0 18579      2 0x00000000
[11359624.902660] Workqueue: events hid_reset [usbhid]
[11359624.902662]  ffff8803f27af850 0000000000000046 ffff8800badb9800 ffff8803f27affd8
[11359624.902666]  0000000000013180 0000000000013180 ffff8800badb9800 ffff8803f27af998
[11359624.902669]  ffff8803f27af9a0 7fffffffffffffff ffff8800badb9800 ffff8800badb9800
[11359624.902673] Call Trace:
...
[11359745.001438] INFO: task khubd:71 blocked for more than 120 seconds.
[11359745.011708]       Not tainted 3.13.0-85-generic #129-Ubuntu
[11359745.021981] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[11359745.042819] khubd           D ffff88043fc93180     0    71      2 0x00000000
[11359745.042825]  ffff880428cd7c80 0000000000000046 ffff8804293d6000 ffff880428cd7fd8
[11359745.042830]  0000000000013180 0000000000013180 ffff8804293d6000 ffff880428c290e8
[11359745.042834]  ffff880428c290ec ffff8804293d6000 00000000ffffffff ffff880428c290f0
[11359745.042838] Call Trace: