If you encounter uvc_disconnect then you may have a different issue
than I do.  I can clearly see via debugging that uvc_disconnect is
never reached.  In my case the disconnect is happening in
usb/core/hub.c:usb_disconnect. The comment on top if this function
says "This call is synchronous, and may not be used in an interrupt
context" though I can clearly see that during uvc initialization it is
being triggered by interrupt (the device disconnecting itself).  So
the disconnect comes unexpectedly via interrupt from hub, not from
uvc_video.  Maybe there are two separate issues?

https://github.com/torvalds/linux/blob/99613159ad749543621da8238acf1a122880144e/drivers/usb/core/hub.c#L2263
*pdev = NULL;

On Tue, Jan 18, 2022 at 2:50 PM Kai-Heng Feng
<email address hidden> wrote:
>
> The issue is that uvc_disconnect() set the USB intf to NULL, but still
> kept the uvcvideo device registered, hence a NULL pointer deference
> happens afterward.
>
> --
> You received this bug notification because you are subscribed to the bug
> report.
> https://bugs.launchpad.net/bugs/1827452
>
> Title:
>   null pointer dereference in uvcvideo
>
> Status in linux package in Ubuntu:
>   Confirmed
>
> Bug description:
>   I have a logitech c920 webcam. When using this camera in obs-studio
>   v23.x, all of my USB devices stop working and I see the following in
>   my kernel log:
>
>   [  590.282211] usb 3-3: new high-speed USB device number 5 using xhci_hcd
>   [  592.660916] usb 3-3: New USB device found, idVendor=046d, idProduct=082d, bcdDevice= 0.11
>   [  592.660922] usb 3-3: New USB device strings: Mfr=0, Product=2, SerialNumber=1
>   [  592.660925] usb 3-3: Product: HD Pro Webcam C920
>   [  592.660928] usb 3-3: SerialNumber: 2EAD866F
>   [  592.664600] uvcvideo: Found UVC 1.00 device HD Pro Webcam C920 (046d:082d)
>   [  592.666416] uvcvideo 3-3:1.0: Entity type for entity Processing 3 was not initialized!
>   [  592.666421] uvcvideo 3-3:1.0: Entity type for entity Extension 6 was not initialized!
>   [  592.666425] uvcvideo 3-3:1.0: Entity type for entity Extension 12 was not initialized!
>   [  592.666428] uvcvideo 3-3:1.0: Entity type for entity Camera 1 was not initialized!
>   [  592.666430] uvcvideo 3-3:1.0: Entity type for entity Extension 8 was not initialized!
>   [  592.666433] uvcvideo 3-3:1.0: Entity type for entity Extension 9 was not initialized!
>   [  592.666436] uvcvideo 3-3:1.0: Entity type for entity Extension 10 was not initialized!
>   [  592.666439] uvcvideo 3-3:1.0: Entity type for entity Extension 11 was not initialized!
>   [  592.666622] input: HD Pro Webcam C920 as /devices/pci0000:00/0000:00:14.0/usb3/3-3/3-3:1.0/input/input23
>   [  748.490453] usb 3-3: reset high-speed USB device number 5 using xhci_hcd
>   [  938.125745] usb 3-3: USB disconnect, device number 5
>   [  943.298530] BUG: unable to handle kernel NULL pointer dereference at 0000000000000000
>   [  943.298533] #PF error: [normal kernel read fault]
>   [  943.298534] PGD 80000007ca5f3067 P4D 80000007ca5f3067 PUD 0
>   [  943.298536] Oops: 0000 [#1] SMP PTI
>   [  943.298538] CPU: 0 PID: 9442 Comm: libobs: graphic Tainted: P           OE     5.0.0-13-generic #14-Ubuntu
>   [  943.298539] Hardware name: Gigabyte Technology Co., Ltd. Z87-HD3/Z87-HD3, BIOS F7 01/20/2014
>   [  943.298543] RIP: 0010:usb_ifnum_to_if+0x24/0x60
>   [  943.298544] Code: ff c3 0f 1f 40 00 0f 1f 44 00 00 55 48 8b 87 c0 03 00 00 48 89 e5 48 85 c0 74 43 0f b6 48 04 84 c9 74 39 48 8b 90 98 00 00 00 <48> 8b 3a 0f b6 7f 02 39 fe 74 2b 48 8d 90 a0 00 00 00 8d 41 ff 48
>   [  943.298545] RSP: 0018:ffffbdae493dbab0 EFLAGS: 00010202
>   [  943.298547] RAX: ffffa106ae527000 RBX: ffffa1070ad0a800 RCX: 0000000000000004
>   [  943.298547] RDX: 0000000000000000 RSI: 0000000000000001 RDI: ffffa1070ad0a800
>   [  943.298548] RBP: ffffbdae493dbab0 R08: 0000000000027040 R09: ffffffffb57825b8
>   [  943.298549] R10: fffffba45fce4bc0 R11: 0000000000000001 R12: 0000000000000000
>   [  943.298550] R13: ffffa10644187b98 R14: 00000000ffffff92 R15: ffffa1075131a000
>   [  943.298551] FS:  00007f93c40d7700(0000) GS:ffffa1075ea00000(0000) knlGS:0000000000000000
>   [  943.298552] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>   [  943.298553] CR2: 0000000000000000 CR3: 00000006f8a94004 CR4: 00000000001606f0
>   [  943.298553] Call Trace:
>   [  943.298557]  usb_hcd_alloc_bandwidth+0x241/0x370
>   [  943.298559]  usb_set_interface+0xfc/0x380
>   [  943.298565]  uvc_video_start_transfer+0x155/0x4b0 [uvcvideo]
>   [  943.298568]  uvc_video_start_streaming+0x7f/0xd0 [uvcvideo]
>   [  943.298570]  uvc_start_streaming+0x28/0x70 [uvcvideo]
>   [  943.298573]  vb2_start_streaming+0x6d/0x110 [videobuf2_common]
>   [  943.298575]  vb2_core_streamon+0x59/0xc0 [videobuf2_common]
>   [  943.298578]  vb2_streamon+0x18/0x30 [videobuf2_v4l2]
>   [  943.298580]  uvc_queue_streamon+0x2e/0x50 [uvcvideo]
>   [  943.298582]  uvc_ioctl_streamon+0x3f/0x60 [uvcvideo]
>   [  943.298588]  v4l_streamon+0x20/0x30 [videodev]
>   [  943.298592]  __video_do_ioctl+0x19a/0x3f0 [videodev]
>   [  943.298596]  video_usercopy+0x1a6/0x660 [videodev]
>   [  943.298599]  ? v4l_s_fmt+0x630/0x630 [videodev]
>   [  943.298603]  video_ioctl2+0x15/0x20 [videodev]
>   [  943.298606]  v4l2_ioctl+0x49/0x50 [videodev]
>   [  943.298608]  do_vfs_ioctl+0xa9/0x640
>   [  943.298610]  ? __switch_to_asm+0x34/0x70
>   [  943.298611]  ? __switch_to_asm+0x40/0x70
>   [  943.298612]  ? __switch_to_asm+0x34/0x70
>   [  943.298612]  ? __switch_to_asm+0x40/0x70
>   [  943.298613]  ? __switch_to_asm+0x34/0x70
>   [  943.298614]  ? __switch_to_asm+0x40/0x70
>   [  943.298615]  ? __switch_to_asm+0x34/0x70
>   [  943.298616]  ? __switch_to_asm+0x40/0x70
>   [  943.298617]  ksys_ioctl+0x67/0x90
>   [  943.298619]  __x64_sys_ioctl+0x1a/0x20
>   [  943.298621]  do_syscall_64+0x5a/0x110
>   [  943.298622]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
>   [  943.298623] RIP: 0033:0x7f9430e082e9
>   [  943.298624] Code: 00 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 77 cb 0c 00 f7 d8 64 89 01 48
>   [  943.298625] RSP: 002b:00007f93c40d6428 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
>   [  943.298626] RAX: ffffffffffffffda RBX: 00007f94000da020 RCX: 00007f9430e082e9
>   [  943.298627] RDX: 00007f93c40d6444 RSI: 0000000040045612 RDI: 000000000000003b
>   [  943.298628] RBP: 0000000000000000 R08: 00000000c058560f R09: 000055f3e344a6e0
>   [  943.298629] R10: 0000000000000000 R11: 0000000000000246 R12: 000000000000003b
>   [  943.298629] R13: 00007f93c40d68bc R14: 00007f94000da020 R15: 0000000000000000
>   [  943.298631] Modules linked in: uvcvideo videobuf2_vmalloc videobuf2_memops videobuf2_v4l2 videobuf2_common snd_usb_audio videodev snd_usbmidi_lib media rfcomm joydev input_leds hid_generic uhid hid algif_hash algif_skcipher af_alg nf_conntrack_netlink nfnetlink xfrm_user xfrm_algo xt_addrtype xt_conntrack br_netfilter veth ebtable_filter ebtables ip6t_MASQUERADE ip6table_nat nf_nat_ipv6 ip6table_filter ip6_tables ipt_MASQUERADE xt_CHECKSUM xt_comment xt_tcpudp iptable_nat nf_nat_ipv4 nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 iptable_mangle iptable_filter bpfilter bridge stp llc aufs overlay pci_stub vboxpci(OE) vboxnetadp(OE) vboxnetflt(OE) cmac bnep vboxdrv(OE) binfmt_misc nvidia_uvm(OE) nls_iso8859_1 intel_rapl x86_pkg_temp_thermal intel_powerclamp kvm_intel kvm irqbypass snd_hda_codec_hdmi crct10dif_pclmul crc32_pclmul ghash_clmulni_intel nvidia_drm(POE) nvidia_modeset(POE) arc4 btusb btrtl btbcm btintel nvidia(POE) snd_hda_codec_realtek bluetooth aesni_intel
>   [  943.298652]  snd_hda_codec_generic ledtrig_audio aes_x86_64 snd_hda_intel crypto_simd snd_hda_codec cryptd ecdh_generic glue_helper iwlmvm snd_hda_core mac80211 snd_hwdep snd_pcm intel_cstate intel_rapl_perf snd_seq_midi snd_seq_midi_event snd_rawmidi iwlwifi drm_kms_helper drm snd_seq ipmi_devintf ipmi_msghandler fb_sys_fops syscopyarea snd_seq_device sysfillrect cfg80211 snd_timer sysimgblt snd soundcore mei_me mei mac_hid sch_fq_codel it87 hwmon_vid coretemp parport_pc ppdev lp parport ip_tables x_tables autofs4 xfs raid10 raid456 async_raid6_recov async_memcpy async_pq async_xor async_tx xor raid6_pq libcrc32c raid1 raid0 multipath linear dm_mirror dm_region_hash dm_log i2c_i801 ahci lpc_ich libahci r8169 realtek video
>   [  943.298672] CR2: 0000000000000000
>   [  943.298674] ---[ end trace 62d503b51a37a64a ]---
>   [  943.298675] RIP: 0010:usb_ifnum_to_if+0x24/0x60
>   [  943.298676] Code: ff c3 0f 1f 40 00 0f 1f 44 00 00 55 48 8b 87 c0 03 00 00 48 89 e5 48 85 c0 74 43 0f b6 48 04 84 c9 74 39 48 8b 90 98 00 00 00 <48> 8b 3a 0f b6 7f 02 39 fe 74 2b 48 8d 90 a0 00 00 00 8d 41 ff 48
>   [  943.298677] RSP: 0018:ffffbdae493dbab0 EFLAGS: 00010202
>   [  943.298678] RAX: ffffa106ae527000 RBX: ffffa1070ad0a800 RCX: 0000000000000004
>   [  943.298679] RDX: 0000000000000000 RSI: 0000000000000001 RDI: ffffa1070ad0a800
>   [  943.298680] RBP: ffffbdae493dbab0 R08: 0000000000027040 R09: ffffffffb57825b8
>   [  943.298680] R10: fffffba45fce4bc0 R11: 0000000000000001 R12: 0000000000000000
>   [  943.298681] R13: ffffa10644187b98 R14: 00000000ffffff92 R15: ffffa1075131a000
>   [  943.298682] FS:  00007f93c40d7700(0000) GS:ffffa1075ea00000(0000) knlGS:0000000000000000
>   [  943.298683] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>   [  943.298684] CR2: 0000000000000000 CR3: 00000006f8a94004 CR4: 00000000001606f0
>
>   Interestingly, this doesn't crash the machine, but it does seem to
>   crash udev or whatever is responsible for updating USB device state,
>   as I've disconnected the webcam but running lsusb still shows it as
>   connected. This is something of a pain as the only way I could file
>   this report was to ssh in from another machine with X forwarding
>   enabled, as my keyboard and mouse no longer function.
>
>   Note that sometimes OBS will work fine with this camera, however this
>   bug will still occur when I attempt to change the camera resolution.
>
>   ProblemType: Bug
>   DistroRelease: Ubuntu 19.04
>   Package: linux-modules-extra-5.0.0-13-generic 5.0.0-13.14
>   ProcVersionSignature: Ubuntu 5.0.0-13.14-generic 5.0.6
>   Uname: Linux 5.0.0-13-generic x86_64
>   NonfreeKernelModules: nvidia_modeset nvidia
>   ApportVersion: 2.20.10-0ubuntu27
>   Architecture: amd64
>   AudioDevicesInUse:
>    USER        PID ACCESS COMMAND
>    /dev/snd/controlC1:  bburns     3961 F.... pulseaudio
>    /dev/snd/pcmC1D7p:   bburns     3961 F...m pulseaudio
>    /dev/snd/controlC0:  bburns     3961 F.... pulseaudio
>    /dev/snd/pcmC0D1c:   bburns     3961 F...m pulseaudio
>   Date: Thu May  2 18:47:59 2019
>   HibernationDevice: RESUME=none
>   InstallationDate: Installed on 2018-07-30 (276 days ago)
>   InstallationMedia: Ubuntu 18.04.1 LTS "Bionic Beaver" - Release amd64 (20180725)
>   MachineType: Gigabyte Technology Co., Ltd. Z87-HD3
>   ProcEnviron:
>    TERM=xterm-256color
>    PATH=(custom, no user)
>    XDG_RUNTIME_DIR=<set>
>    LANG=en_US.UTF-8
>    SHELL=/bin/bash
>   ProcFB: 0 EFI VGA
>   ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-5.0.0-13-generic root=/dev/mapper/cl_box-root ro
>   RelatedPackageVersions:
>    linux-restricted-modules-5.0.0-13-generic N/A
>    linux-backports-modules-5.0.0-13-generic  N/A
>    linux-firmware                            1.178
>   SourcePackage: linux
>   UpgradeStatus: Upgraded to disco on 2019-04-24 (8 days ago)
>   dmi.bios.date: 01/20/2014
>   dmi.bios.vendor: American Megatrends Inc.
>   dmi.bios.version: F7
>   dmi.board.asset.tag: To be filled by O.E.M.
>   dmi.board.name: Z87-HD3
>   dmi.board.vendor: Gigabyte Technology Co., Ltd.
>   dmi.board.version: To be filled by O.E.M.
>   dmi.chassis.asset.tag: To Be Filled By O.E.M.
>   dmi.chassis.type: 3
>   dmi.chassis.vendor: Gigabyte Technology Co., Ltd.
>   dmi.chassis.version: To Be Filled By O.E.M.
>   dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvrF7:bd01/20/2014:svnGigabyteTechnologyCo.,Ltd.:pnZ87-HD3:pvrTobefilledbyO.E.M.:rvnGigabyteTechnologyCo.,Ltd.:rnZ87-HD3:rvrTobefilledbyO.E.M.:cvnGigabyteTechnologyCo.,Ltd.:ct3:cvrToBeFilledByO.E.M.:
>   dmi.product.family: To be filled by O.E.M.
>   dmi.product.name: Z87-HD3
>   dmi.product.sku: To be filled by O.E.M.
>   dmi.product.version: To be filled by O.E.M.
>   dmi.sys.vendor: Gigabyte Technology Co., Ltd.
>
> To manage notifications about this bug go to:
> https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1827452/+subscriptions
>