URB submitted while active

[fabled]

I got the following backtrace while testing this driver:
[ 3098.930049] ------------[ cut here ]------------
[ 3098.930077] WARNING: CPU: 2 PID: 4940 at /home/buildozer/aports/main/linux-grsec/src/linux-3.14/drivers/usb/core/urb.c:339 usb_submit_urb+0x65/0x467 usbcore
[ 3098.930079] URB ffff88020d801cc0 submitted while active
[ 3098.930080] Modules linked in: ipv6 usb_it950x(O) kvm_intel kvm af_packet shpchp hid_multitouch smsc75xx usbnet mii btusb bluetooth 6lowpan_iphc uvcvideo usbhid videobuf2_core videodev media videobuf2_vmalloc videobuf2_memops snd_hda_codec_hdmi joydev mousedev i2c_hid hid arc4 battery iTCO_wdt iTCO_vendor_support ac thermal dell_wmi sparse_keymap iwlmvm mac80211 lpc_ich snd_hda_codec_realtek mfd_core i915 snd_hda_codec_generic drm_kms_helper drm intel_gtt agpgart cfbfillrect cfbimgblt i2c_algo_bit cfbcopyarea processor iwlwifi snd_hda_intel snd_hda_codec cfg80211 snd_hwdep snd_pcm snd_timer rfkill snd mei_me mei firmware_class soundcore pcspkr serio_raw psmouse evdev fbcon font bitblit fbcon_rotate fbcon_ccw fbcon_ud fbcon_cw softcursor tileblit fb fbdev xhci_hcd ehci_pci ehci_hcd i2c_i801 ahci libahci
[ 3098.930117] libata wmi video backlight button i2c_designware_platform i2c_designware_core i2c_core loop ext4 mbcache jbd2 crc16 usb_storage usbcore usb_common sd_mod scsi_mod crc_t10dif crct10dif_common
[ 3098.930129] CPU: 2 PID: 4940 Comm: sendts Tainted: G O 3.14.15-1-grsec #2-Alpine
[ 3098.930130] Hardware name: Dell Inc. XPS13 9333/0D13CR, BIOS A04 03/19/2014
[ 3098.930132] 0000000000000000 ffffc9001e6c3d48 ffffffff8132e9a4 ffffc9001e6c3d90
[ 3098.930135] ffffc9001e6c3d80 ffffffff8103e598 ffffffffa005e8aa ffff88020d801cc0
[ 3098.930137] 0000000000000000 00000000fffffff0 000000000002de60 ffffc9001e6c3de0
[ 3098.930140] Call Trace:
[ 3098.930146] [] dump_stack+0x45/0x56
[ 3098.930151] [] warn_slowpath_common+0x75/0x8e
[ 3098.930163] [] ? usb_submit_urb+0x65/0x467 [usbcore]
[ 3098.930166] [] warn_slowpath_fmt+0x47/0x49
[ 3098.930178] [] ? .LC9+0x21a/0x195c [usbcore]
[ 3098.930189] [] usb_submit_urb+0x65/0x467 [usbcore]
[ 3098.930192] [] ? schedule+0x6e/0x70
[ 3098.930196] [] it950x_tx_write+0x196/0x205 [usb_it950x]
[ 3098.930200] [] ? ptrace_do_notify+0x90/0x9b
[ 3098.930203] [] vfs_write+0x121/0x20d
[ 3098.930206] [] SyS_write+0x42/0x86
[ 3098.930209] [] tracesys+0xc8/0xcd
[ 3098.930211] ---[ end trace eb378f9afffbd2d6 ]---
[ 3098.930212] tx_stop_urb_transfer() end
[ 3107.726766] tx_stop_urb_transfer: iso xfer already stop!
[ 3107.726771] - Enter DL_ApPwCtrl Function -
[ 3107.726773] bOn = OFF
[ 3107.831913] IT950x Power OFF