Re: [syzbot] [usb?] [media?] possible deadlock in vb2_video_unregister_device

[Tomasz Figa]

On Wed, Feb 7, 2024 at 5:44 PM syzbot
<syzbot+3b1d4b3d5f7a358bf9a9@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
>
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    ed5551279c91 Merge 6.8-rc3 into usb-next
> git tree:       https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git usb-testing
> console output: https://syzkaller.appspot.com/x/log.txt?x=16940d7be80000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=28a3704ea90ef255
> dashboard link: https://syzkaller.appspot.com/bug?extid=3b1d4b3d5f7a358bf9a9
> compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=14450a38180000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1603629fe80000
>
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/10b543a7171a/disk-ed555127.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/dc10f27643e8/vmlinux-ed555127.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/bb6389e754b9/bzImage-ed555127.xz
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+3b1d4b3d5f7a358bf9a9@xxxxxxxxxxxxxxxxxxxxxxxxx
>
> usb 1-1: SerialNumber: syz
> usb 1-1: config 0 descriptor??
> usbtv 1-1:0.0: Fushicai USBTV007 Audio-Video Grabber
> usb 1-1: USB disconnect, device number 2
> ============================================
> WARNING: possible recursive locking detected
> 6.8.0-rc3-syzkaller-00047-ged5551279c91 #0 Not tainted
> --------------------------------------------
> kworker/0:2/694 is trying to acquire lock:
> ffff888109f20b70 (&usbtv->vb2q_lock){+.+.}-{3:3}, at: vb2_video_unregister_device drivers/media/common/videobuf2/videobuf2-v4l2.c:1269 [inline]
> ffff888109f20b70 (&usbtv->vb2q_lock){+.+.}-{3:3}, at: vb2_video_unregister_device+0x12b/0x2d0 drivers/media/common/videobuf2/videobuf2-v4l2.c:1245
>
> but task is already holding lock:
> ffff888109f20b70 (&usbtv->vb2q_lock){+.+.}-{3:3}, at: usbtv_video_free+0x28/0x70 drivers/media/usb/usbtv/usbtv-video.c:966
>

Looking at usbtv_video_free [1], it calls
vb2_video_unregister_device() with the queue mutex locked, which is
just wrong. I wonder how (and if) it even worked before. Laurent,
Hans, Mauro, any idea who is maintaining this driver? I don't see a
matching entry in the MAINTAINERS file.

[1] https://elixir.bootlin.com/linux/v6.8-rc4/source/drivers/media/usb/usbtv/usbtv-video.c#L964

Best regards,
Tomasz

> other info that might help us debug this:
>  Possible unsafe locking scenario:
>
>        CPU0
>        ----
>   lock(&usbtv->vb2q_lock);
>   lock(&usbtv->vb2q_lock);
>
>  *** DEADLOCK ***
>
>  May be due to missing lock nesting notation
>
> 7 locks held by kworker/0:2/694:
>  #0: ffff888106ad2138 ((wq_completion)usb_hub_wq){+.+.}-{0:0}, at: process_one_work+0x789/0x15d0 kernel/workqueue.c:2608
>  #1: ffffc90001c0fd80 ((work_completion)(&hub->events)){+.+.}-{0:0}, at: process_one_work+0x7eb/0x15d0 kernel/workqueue.c:2609
>  #2: ffff88810af2f190 (&dev->mutex){....}-{3:3}, at: device_lock include/linux/device.h:990 [inline]
>  #2: ffff88810af2f190 (&dev->mutex){....}-{3:3}, at: hub_event+0x1be/0x4f40 drivers/usb/core/hub.c:5840
>  #3: ffff888107799190 (&dev->mutex){....}-{3:3}, at: device_lock include/linux/device.h:990 [inline]
>  #3: ffff888107799190 (&dev->mutex){....}-{3:3}, at: usb_disconnect+0x10a/0x910 drivers/usb/core/hub.c:2287
>  #4: ffff88810779a160 (&dev->mutex){....}-{3:3}, at: device_lock include/linux/device.h:990 [inline]
>  #4: ffff88810779a160 (&dev->mutex){....}-{3:3}, at: __device_driver_lock drivers/base/dd.c:1095 [inline]
>  #4: ffff88810779a160 (&dev->mutex){....}-{3:3}, at: device_release_driver_internal+0xa4/0x610 drivers/base/dd.c:1292
>  #5: ffff888109f20b70 (&usbtv->vb2q_lock){+.+.}-{3:3}, at: usbtv_video_free+0x28/0x70 drivers/media/usb/usbtv/usbtv-video.c:966
>  #6: ffff888109f20ae0 (&usbtv->v4l2_lock){+.+.}-{3:3}, at: usbtv_video_free+0x32/0x70 drivers/media/usb/usbtv/usbtv-video.c:967
>
> stack backtrace:
> CPU: 0 PID: 694 Comm: kworker/0:2 Not tainted 6.8.0-rc3-syzkaller-00047-ged5551279c91 #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/25/2024
> Workqueue: usb_hub_wq hub_event
> Call Trace:
>  <TASK>
>  __dump_stack lib/dump_stack.c:88 [inline]
>  dump_stack_lvl+0xd9/0x1b0 lib/dump_stack.c:106
>  check_deadlock kernel/locking/lockdep.c:3062 [inline]
>  validate_chain kernel/locking/lockdep.c:3856 [inline]
>  __lock_acquire+0x210a/0x3b30 kernel/locking/lockdep.c:5137
>  lock_acquire kernel/locking/lockdep.c:5754 [inline]
>  lock_acquire+0x1ae/0x520 kernel/locking/lockdep.c:5719
>  __mutex_lock_common kernel/locking/mutex.c:608 [inline]
>  __mutex_lock+0x175/0x9d0 kernel/locking/mutex.c:752
>  vb2_video_unregister_device drivers/media/common/videobuf2/videobuf2-v4l2.c:1269 [inline]
>  vb2_video_unregister_device+0x12b/0x2d0 drivers/media/common/videobuf2/videobuf2-v4l2.c:1245
>  usbtv_video_free+0x4a/0x70 drivers/media/usb/usbtv/usbtv-video.c:970
>  usbtv_disconnect+0x5c/0xd0 drivers/media/usb/usbtv/usbtv-core.c:138
>  usb_unbind_interface+0x1e5/0x960 drivers/usb/core/driver.c:461
>  device_remove drivers/base/dd.c:569 [inline]
>  device_remove+0x11f/0x170 drivers/base/dd.c:561
>  __device_release_driver drivers/base/dd.c:1272 [inline]
>  device_release_driver_internal+0x44a/0x610 drivers/base/dd.c:1295
>  bus_remove_device+0x22c/0x420 drivers/base/bus.c:574
>  device_del+0x39a/0xa50 drivers/base/core.c:3814
>  usb_disable_device+0x36c/0x7f0 drivers/usb/core/message.c:1416
>  usb_disconnect+0x2e1/0x910 drivers/usb/core/hub.c:2296
>  hub_port_connect drivers/usb/core/hub.c:5352 [inline]
>  hub_port_connect_change drivers/usb/core/hub.c:5652 [inline]
>  port_event drivers/usb/core/hub.c:5812 [inline]
>  hub_event+0x1be0/0x4f40 drivers/usb/core/hub.c:5894
>  process_one_work+0x886/0x15d0 kernel/workqueue.c:2633
>  process_scheduled_works kernel/workqueue.c:2706 [inline]
>  worker_thread+0x8b9/0x1290 kernel/workqueue.c:2787
>  kthread+0x2c6/0x3a0 kernel/kthread.c:388
>  ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:147
>  ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:242
>  </TASK>
>
>
> ---
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