syzbot

======================================================
WARNING: possible circular locking dependency detected
5.15.185-syzkaller #0 Not tainted
------------------------------------------------------
syz.0.16/4288 is trying to acquire lock:
ffff88801f53cc28 ((work_completion)(&hdev->bg_scan_update)){+.+.}-{0:0}, at: __flush_work+0xc1/0x1b0 kernel/workqueue.c:3090

but task is already holding lock:
ffffffff8d4b2748 (rfkill_global_mutex){+.+.}-{3:3}, at: rfkill_fop_write+0x19e/0x560 net/rfkill/core.c:1266

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #4 (rfkill_global_mutex){+.+.}-{3:3}:
       __mutex_lock_common+0x1eb/0x2390 kernel/locking/mutex.c:596
       __mutex_lock kernel/locking/mutex.c:729 [inline]
       mutex_lock_nested+0x17/0x20 kernel/locking/mutex.c:743
       rfkill_register+0x33/0x8a0 net/rfkill/core.c:1045
       hci_register_dev+0x452/0x970 net/bluetooth/hci_core.c:3960
       __vhci_create_device drivers/bluetooth/hci_vhci.c:129 [inline]
       vhci_create_device+0x32c/0x5c0 drivers/bluetooth/hci_vhci.c:153
       vhci_get_user drivers/bluetooth/hci_vhci.c:210 [inline]
       vhci_write+0x391/0x450 drivers/bluetooth/hci_vhci.c:290
       call_write_iter include/linux/fs.h:2172 [inline]
       new_sync_write fs/read_write.c:507 [inline]
       vfs_write+0x712/0xd00 fs/read_write.c:594
       ksys_write+0x14d/0x250 fs/read_write.c:647
       do_syscall_x64 arch/x86/entry/common.c:50 [inline]
       do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
       entry_SYSCALL_64_after_hwframe+0x66/0xd0

-> #3 (&data->open_mutex){+.+.}-{3:3}:
       __mutex_lock_common+0x1eb/0x2390 kernel/locking/mutex.c:596
       __mutex_lock kernel/locking/mutex.c:729 [inline]
       mutex_lock_nested+0x17/0x20 kernel/locking/mutex.c:743
       vhci_send_frame+0x88/0x100 drivers/bluetooth/hci_vhci.c:71
       hci_send_frame+0x1a9/0x2e0 net/bluetooth/hci_core.c:4256
       hci_sched_acl_pkt net/bluetooth/hci_core.c:4781 [inline]
       hci_sched_acl net/bluetooth/hci_core.c:4866 [inline]
       hci_tx_work+0x9f9/0x1710 net/bluetooth/hci_core.c:4932
       process_one_work+0x863/0x1000 kernel/workqueue.c:2310
       worker_thread+0xaa8/0x12a0 kernel/workqueue.c:2457
       kthread+0x436/0x520 kernel/kthread.c:334
       ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287

-> #2 ((work_completion)(&hdev->tx_work)){+.+.}-{0:0}:
       __flush_work+0xdd/0x1b0 kernel/workqueue.c:3090
       hci_dev_do_close+0x1e7/0x1030 net/bluetooth/hci_core.c:1756
       hci_unregister_dev+0x2d7/0x580 net/bluetooth/hci_core.c:4040
       vhci_release+0x73/0xc0 drivers/bluetooth/hci_vhci.c:345
       __fput+0x234/0x930 fs/file_table.c:311
       task_work_run+0x125/0x1a0 kernel/task_work.c:188
       exit_task_work include/linux/task_work.h:33 [inline]
       do_exit+0x616/0x20a0 kernel/exit.c:874
       do_group_exit+0x12e/0x300 kernel/exit.c:996
       get_signal+0x6ca/0x12c0 kernel/signal.c:2900
       arch_do_signal_or_restart+0xc1/0x1300 arch/x86/kernel/signal.c:867
       handle_signal_work kernel/entry/common.c:154 [inline]
       exit_to_user_mode_loop+0x9e/0x130 kernel/entry/common.c:178
       exit_to_user_mode_prepare+0xb1/0x140 kernel/entry/common.c:214
       __syscall_exit_to_user_mode_work kernel/entry/common.c:296 [inline]
       syscall_exit_to_user_mode+0x16/0x40 kernel/entry/common.c:307
       do_syscall_64+0x58/0xa0 arch/x86/entry/common.c:86
       entry_SYSCALL_64_after_hwframe+0x66/0xd0

-> #1 (&hdev->req_lock){+.+.}-{3:3}:
       __mutex_lock_common+0x1eb/0x2390 kernel/locking/mutex.c:596
       __mutex_lock kernel/locking/mutex.c:729 [inline]
       mutex_lock_nested+0x17/0x20 kernel/locking/mutex.c:743
       hci_req_sync net/bluetooth/hci_request.c:278 [inline]
       bg_scan_update+0x44/0x3b0 net/bluetooth/hci_request.c:2952
       process_one_work+0x863/0x1000 kernel/workqueue.c:2310
       worker_thread+0xaa8/0x12a0 kernel/workqueue.c:2457
       kthread+0x436/0x520 kernel/kthread.c:334
       ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287

-> #0 ((work_completion)(&hdev->bg_scan_update)){+.+.}-{0:0}:
       check_prev_add kernel/locking/lockdep.c:3053 [inline]
       check_prevs_add kernel/locking/lockdep.c:3172 [inline]
       validate_chain kernel/locking/lockdep.c:3788 [inline]
       __lock_acquire+0x2c33/0x7c60 kernel/locking/lockdep.c:5012
       lock_acquire+0x197/0x3f0 kernel/locking/lockdep.c:5623
       __flush_work+0xdd/0x1b0 kernel/workqueue.c:3090
       __cancel_work_timer+0x3ac/0x520 kernel/workqueue.c:3181
       hci_request_cancel_all+0xcc/0x300 net/bluetooth/hci_request.c:3522
       hci_dev_do_close+0x4e/0x1030 net/bluetooth/hci_core.c:1736
       hci_rfkill_set_block+0x10a/0x190 net/bluetooth/hci_core.c:2235
       rfkill_set_block+0x1c6/0x420 net/rfkill/core.c:345
       rfkill_fop_write+0x458/0x560 net/rfkill/core.c:1274
       do_loop_readv_writev fs/read_write.c:-1 [inline]
       do_iter_write+0x3e4/0x7b0 fs/read_write.c:857
       vfs_writev fs/read_write.c:928 [inline]
       do_writev+0x254/0x410 fs/read_write.c:971
       do_syscall_x64 arch/x86/entry/common.c:50 [inline]
       do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
       entry_SYSCALL_64_after_hwframe+0x66/0xd0

other info that might help us debug this:

Chain exists of:
  (work_completion)(&hdev->bg_scan_update) --> &data->open_mutex --> rfkill_global_mutex

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(rfkill_global_mutex);
                               lock(&data->open_mutex);
                               lock(rfkill_global_mutex);
  lock((work_completion)(&hdev->bg_scan_update));

 *** DEADLOCK ***

1 lock held by syz.0.16/4288:
 #0: ffffffff8d4b2748 (rfkill_global_mutex){+.+.}-{3:3}, at: rfkill_fop_write+0x19e/0x560 net/rfkill/core.c:1266

stack backtrace:
CPU: 1 PID: 4288 Comm: syz.0.16 Not tainted 5.15.185-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x168/0x230 lib/dump_stack.c:106
 check_noncircular+0x274/0x310 kernel/locking/lockdep.c:2133
 check_prev_add kernel/locking/lockdep.c:3053 [inline]
 check_prevs_add kernel/locking/lockdep.c:3172 [inline]
 validate_chain kernel/locking/lockdep.c:3788 [inline]
 __lock_acquire+0x2c33/0x7c60 kernel/locking/lockdep.c:5012
 lock_acquire+0x197/0x3f0 kernel/locking/lockdep.c:5623
 __flush_work+0xdd/0x1b0 kernel/workqueue.c:3090
 __cancel_work_timer+0x3ac/0x520 kernel/workqueue.c:3181
 hci_request_cancel_all+0xcc/0x300 net/bluetooth/hci_request.c:3522
 hci_dev_do_close+0x4e/0x1030 net/bluetooth/hci_core.c:1736
 hci_rfkill_set_block+0x10a/0x190 net/bluetooth/hci_core.c:2235
 rfkill_set_block+0x1c6/0x420 net/rfkill/core.c:345
 rfkill_fop_write+0x458/0x560 net/rfkill/core.c:1274
 do_loop_readv_writev fs/read_write.c:-1 [inline]
 do_iter_write+0x3e4/0x7b0 fs/read_write.c:857
 vfs_writev fs/read_write.c:928 [inline]
 do_writev+0x254/0x410 fs/read_write.c:971
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7fb6b9a4f929
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffe3081cac8 EFLAGS: 00000246 ORIG_RAX: 0000000000000014
RAX: ffffffffffffffda RBX: 00007fb6b9c76fa0 RCX: 00007fb6b9a4f929
RDX: 0000000000000001 RSI: 0000200000000440 RDI: 0000000000000003
RBP: 00007fb6b9ad1b39 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fb6b9c76fa0 R14: 00007fb6b9c76fa0 R15: 0000000000000003
 </TASK>