I think the NULL pointer dereference is red herring here, the disconnection is 
where problem occurs:
júl 22 21:12:50 lenovo kernel: usb 3-2: USB disconnect, device number 2

So we need to know why the webcam disconnected right before it starts streaming.
Please add "xhci-pci.dyndbg=+p xhci-hcd.dyndbg=+p usbcore.dyndbg=+p" to the 
kernel parameter, reproduce the bug, then attach dmesg.

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  Lenovo e73 USB webcam problems

Status in linux package in Ubuntu:

Bug description:
  I'm experiencing problems with USB webcam on Lenovo e73 with Ubuntu
  16.04.2 Xenial 32bit.

  Originally with 4.4 connecting the camera often resulted in complete
  hang of the system (apparently not even SysRq worked, though I did not
  test that personally since it is a system I'm administering remotely
  for a family member). There was always a null pointer dereference just
  before the hang, so I suspect that is the culprit (see the attached
  kernel log).

  After some updates the system no longer hangs. I suspect this was fixed by 
going from linux 4.4 to 4.8. However, the webcam still often doesn't work and 
most application just return error. This is usually fixed after several tries, 
but sometimes it is necessary to reboot computer. Updating BIOS didn't help. 
The kernel logs still contain the same null pointer dereference with exactly 
the same stack trace for both 4.8 and 4.10.
  ApportVersion: 2.20.1-0ubuntu2.10
  Architecture: i386
   /dev/snd/controlC2:  user       1852 F.... pulseaudio
   /dev/snd/controlC0:  user       1852 F.... pulseaudio
   /dev/snd/controlC1:  user       1852 F.... pulseaudio
  DistroRelease: Ubuntu 16.04
  HibernationDevice: RESUME=UUID=de34a223-a620-435a-974a-e29dad30f1ac
  InstallationDate: Installed on 2017-05-05 (85 days ago)
  InstallationMedia: Ubuntu 15.10 "Wily Werewolf" - Release i386 (20151021)
   tun0      no wireless extensions.
   enp2s0    no wireless extensions.
   lo        no wireless extensions.
  MachineType: LENOVO 10DR002SMC
  Package: linux (not installed)
   PATH=(custom, no user)
  ProcFB: 0 inteldrmfb
  ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-4.8.0-58-generic 
root=UUID=07f94680-ac2c-498b-86e4-72ff6e4bd18f ro quiet splash 
usbcore.autosuspend=-1 vt.handoff=7
  ProcVersionSignature: Ubuntu 4.8.0-58.63~16.04.1-generic 4.8.17
   Error: command ['pacmd', 'list'] failed with exit code 1: Home directory not 
accessible: Permission denied
   No PulseAudio daemon running, or not running as session daemon.
   linux-restricted-modules-4.8.0-58-generic N/A
   linux-backports-modules-4.8.0-58-generic  N/A
   linux-firmware                            1.157.11
  Tags:  xenial
  Uname: Linux 4.8.0-58-generic i686
  UpgradeStatus: Upgraded to xenial on 2017-05-05 (85 days ago)
  _MarkForUpload: True
  dmi.bios.date: 02/13/2017
  dmi.bios.vendor: LENOVO
  dmi.bios.version: FCKT82AUS
  dmi.board.name: 3098
  dmi.board.vendor: LENOVO
  dmi.board.version: SDK0G00599 WIN
  dmi.chassis.type: 3
  dmi.chassis.vendor: LENOVO
  dmi.product.name: 10DR002SMC
  dmi.product.version: ThinkCentre E73
  dmi.sys.vendor: LENOVO

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