======================================================
WARNING: possible circular locking dependency detected
5.9.0-rc8-syzkaller #0 Not tainted
------------------------------------------------------
v4l_id/3229 is trying to acquire lock:
ffff8881c8a25e00 (&dev->lock#3){+.+.}-{3:3}, at: em28xx_v4l2_open+0xf8/0x570 drivers/media/usb/em28xx/em28xx-video.c:2160

but task is already holding lock:
ffffffff87af0ac8 (videodev_lock){+.+.}-{3:3}, at: v4l2_open+0x20/0x3f0 drivers/media/v4l2-core/v4l2-dev.c:411

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (videodev_lock){+.+.}-{3:3}:
       __mutex_lock_common kernel/locking/mutex.c:956 [inline]
       __mutex_lock+0x134/0x10a0 kernel/locking/mutex.c:1103
       __video_register_device+0x364/0x4b38 drivers/media/v4l2-core/v4l2-dev.c:971
       video_register_device include/media/v4l2-dev.h:384 [inline]
       em28xx_v4l2_init drivers/media/usb/em28xx/em28xx-video.c:2792 [inline]
       em28xx_v4l2_init.cold+0x1b92/0x30ca drivers/media/usb/em28xx/em28xx-video.c:2520
       em28xx_init_extension+0x12f/0x1f0 drivers/media/usb/em28xx/em28xx-core.c:1128
       request_module_async+0x5d/0x70 drivers/media/usb/em28xx/em28xx-cards.c:3338
       process_one_work+0x94c/0x15f0 kernel/workqueue.c:2269
       process_scheduled_works kernel/workqueue.c:2331 [inline]
       worker_thread+0x7da/0x1120 kernel/workqueue.c:2420
       kthread+0x392/0x470 kernel/kthread.c:292
       ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

-> #0 (&dev->lock#3){+.+.}-{3:3}:
       check_prev_add kernel/locking/lockdep.c:2496 [inline]
       check_prevs_add kernel/locking/lockdep.c:2601 [inline]
       validate_chain kernel/locking/lockdep.c:3218 [inline]
       __lock_acquire+0x29bb/0x53b0 kernel/locking/lockdep.c:4441
       lock_acquire+0x18c/0x980 kernel/locking/lockdep.c:5029
       __mutex_lock_common kernel/locking/mutex.c:956 [inline]
       __mutex_lock+0x134/0x10a0 kernel/locking/mutex.c:1103
       em28xx_v4l2_open+0xf8/0x570 drivers/media/usb/em28xx/em28xx-video.c:2160
       v4l2_open+0x203/0x3f0 drivers/media/v4l2-core/v4l2-dev.c:422
       chrdev_open+0x266/0x770 fs/char_dev.c:414
       do_dentry_open+0x4b4/0x1090 fs/open.c:817
       do_open fs/namei.c:3251 [inline]
       path_openat+0x190d/0x2690 fs/namei.c:3368
       do_filp_open+0x17e/0x3c0 fs/namei.c:3395
       do_sys_openat2+0x16d/0x420 fs/open.c:1168
       do_sys_open fs/open.c:1184 [inline]
       __do_sys_open fs/open.c:1192 [inline]
       __se_sys_open fs/open.c:1188 [inline]
       __x64_sys_open+0x119/0x1c0 fs/open.c:1188
       do_syscall_64+0x2d/0x40 arch/x86/entry/common.c:46
       entry_SYSCALL_64_after_hwframe+0x44/0xa9

other info that might help us debug this:

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(videodev_lock);
                               lock(&dev->lock#3);
                               lock(videodev_lock);
  lock(&dev->lock#3);

 *** DEADLOCK ***

1 lock held by v4l_id/3229:
 #0: ffffffff87af0ac8 (videodev_lock){+.+.}-{3:3}, at: v4l2_open+0x20/0x3f0 drivers/media/v4l2-core/v4l2-dev.c:411

stack backtrace:
CPU: 1 PID: 3229 Comm: v4l_id Not tainted 5.9.0-rc8-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x107/0x16e lib/dump_stack.c:118
 check_noncircular+0x324/0x3e0 kernel/locking/lockdep.c:1827
 check_prev_add kernel/locking/lockdep.c:2496 [inline]
 check_prevs_add kernel/locking/lockdep.c:2601 [inline]
 validate_chain kernel/locking/lockdep.c:3218 [inline]
 __lock_acquire+0x29bb/0x53b0 kernel/locking/lockdep.c:4441
 lock_acquire+0x18c/0x980 kernel/locking/lockdep.c:5029
 __mutex_lock_common kernel/locking/mutex.c:956 [inline]
 __mutex_lock+0x134/0x10a0 kernel/locking/mutex.c:1103
 em28xx_v4l2_open+0xf8/0x570 drivers/media/usb/em28xx/em28xx-video.c:2160
 v4l2_open+0x203/0x3f0 drivers/media/v4l2-core/v4l2-dev.c:422
 chrdev_open+0x266/0x770 fs/char_dev.c:414
 do_dentry_open+0x4b4/0x1090 fs/open.c:817
 do_open fs/namei.c:3251 [inline]
 path_openat+0x190d/0x2690 fs/namei.c:3368
 do_filp_open+0x17e/0x3c0 fs/namei.c:3395
 do_sys_openat2+0x16d/0x420 fs/open.c:1168
 do_sys_open fs/open.c:1184 [inline]
 __do_sys_open fs/open.c:1192 [inline]
 __se_sys_open fs/open.c:1188 [inline]
 __x64_sys_open+0x119/0x1c0 fs/open.c:1188
 do_syscall_64+0x2d/0x40 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x7fa93ca16840
Code: 73 01 c3 48 8b 0d 68 77 20 00 f7 d8 64 89 01 48 83 c8 ff c3 66 0f 1f 44 00 00 83 3d 89 bb 20 00 00 75 10 b8 02 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 31 c3 48 83 ec 08 e8 1e f6 ff ff 48 89 04 24
RSP: 002b:00007ffe49d0bbb8 EFLAGS: 00000246 ORIG_RAX: 0000000000000002
RAX: ffffffffffffffda RBX: 00007ffe49d0bd28 RCX: 00007fa93ca16840
RDX: 00007fa93ca02ea0 RSI: 0000000000000000 RDI: 00007ffe49d0cf24
RBP: 0000000000000003 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000002 R11: 0000000000000246 R12: 0000562948d788d0
R13: 00007ffe49d0bd20 R14: 0000000000000000 R15: 0000000000000000