======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Tainted: G             L     
------------------------------------------------------
krfcommd/3370 is trying to acquire lock:
ffff888058eda140 ((wq_completion)hci0#2){+.+.}-{0:0}, at: touch_wq_lockdep_map+0x9c/0x1c0 kernel/workqueue.c:4111

but task is already holding lock:
ffffffff91f84880 (rfcomm_mutex){+.+.}-{4:4}, at: rfcomm_process_sessions net/bluetooth/rfcomm/core.c:2152 [inline]
ffffffff91f84880 (rfcomm_mutex){+.+.}-{4:4}, at: rfcomm_run+0x30b/0x5550 net/bluetooth/rfcomm/core.c:2261

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #4 (rfcomm_mutex){+.+.}-{4:4}:
       lock_acquire kernel/locking/lockdep.c:5942 [inline]
       lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5899
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x1a4/0x1bd0 kernel/locking/mutex.c:821
       rfcomm_security_cfm+0x3f/0x4b0 net/bluetooth/rfcomm/core.c:2279
       hci_encrypt_cfm+0x18e/0x740 include/net/bluetooth/hci_core.h:2243
       hci_encrypt_change_evt+0x92c/0xfb0 net/bluetooth/hci_event.c:3674
       hci_event_func net/bluetooth/hci_event.c:7887 [inline]
       hci_event_packet+0x8e9/0xcd0 net/bluetooth/hci_event.c:7938
       hci_rx_work+0x451/0xfc0 net/bluetooth/hci_core.c:4087
       process_one_work+0xac7/0x1b10 kernel/workqueue.c:3396
       process_scheduled_works kernel/workqueue.c:3479 [inline]
       worker_thread+0x5ef/0xe50 kernel/workqueue.c:3560
       kthread+0x373/0x450 kernel/kthread.c:436
       ret_from_fork+0x730/0xd60 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #3 (hci_cb_list_lock){+.+.}-{4:4}:
       lock_acquire kernel/locking/lockdep.c:5942 [inline]
       lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5899
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x1a4/0x1bd0 kernel/locking/mutex.c:821
       hci_connect_cfm include/net/bluetooth/hci_core.h:2164 [inline]
       hci_remote_features_evt+0x485/0x9b0 net/bluetooth/hci_event.c:3786
       hci_event_func net/bluetooth/hci_event.c:7887 [inline]
       hci_event_packet+0x8e9/0xcd0 net/bluetooth/hci_event.c:7938
       hci_rx_work+0x451/0xfc0 net/bluetooth/hci_core.c:4087
       process_one_work+0xac7/0x1b10 kernel/workqueue.c:3396
       process_scheduled_works kernel/workqueue.c:3479 [inline]
       worker_thread+0x5ef/0xe50 kernel/workqueue.c:3560
       kthread+0x373/0x450 kernel/kthread.c:436
       ret_from_fork+0x730/0xd60 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #2 (&hdev->lock){+.+.}-{4:4}:
       lock_acquire kernel/locking/lockdep.c:5942 [inline]
       lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5899
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x1a4/0x1bd0 kernel/locking/mutex.c:821
       hci_send_cmd_sync net/bluetooth/hci_core.c:4118 [inline]
       hci_cmd_work+0x1be/0x990 net/bluetooth/hci_core.c:4167
       process_one_work+0xac7/0x1b10 kernel/workqueue.c:3396
       process_scheduled_works kernel/workqueue.c:3479 [inline]
       worker_thread+0x5ef/0xe50 kernel/workqueue.c:3560
       kthread+0x373/0x450 kernel/kthread.c:436
       ret_from_fork+0x730/0xd60 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #1 ((work_completion)(&hdev->cmd_work)){+.+.}-{0:0}:
       lock_acquire kernel/locking/lockdep.c:5942 [inline]
       lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5899
       process_one_work+0xa32/0x1b10 kernel/workqueue.c:3372
       process_scheduled_works kernel/workqueue.c:3479 [inline]
       worker_thread+0x5ef/0xe50 kernel/workqueue.c:3560
       kthread+0x373/0x450 kernel/kthread.c:436
       ret_from_fork+0x730/0xd60 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #0 ((wq_completion)hci0#2){+.+.}-{0:0}:
       check_prev_add+0xeb/0xe60 kernel/locking/lockdep.c:3209
       check_prevs_add kernel/locking/lockdep.c:3328 [inline]
       validate_chain kernel/locking/lockdep.c:3952 [inline]
       __lock_acquire+0x1528/0x1f40 kernel/locking/lockdep.c:5288
       lock_acquire kernel/locking/lockdep.c:5942 [inline]
       lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5899
       touch_wq_lockdep_map+0xad/0x1c0 kernel/workqueue.c:4111
       __flush_workqueue+0x131/0x1200 kernel/workqueue.c:4153
       drain_workqueue+0x175/0x3b0 kernel/workqueue.c:4317
       destroy_workqueue+0xc3/0xa30 kernel/workqueue.c:6155
       hci_release_dev+0x116/0x630 net/bluetooth/hci_core.c:2728
       bt_host_release+0x6b/0xb0 net/bluetooth/hci_sysfs.c:100
       device_release+0xd2/0x270 drivers/base/core.c:2640
       kobject_cleanup lib/kobject.c:689 [inline]
       kobject_release lib/kobject.c:720 [inline]
       kref_put include/linux/kref.h:65 [inline]
       kobject_put+0x1f7/0x640 lib/kobject.c:737
       put_device+0x1f/0x30 drivers/base/core.c:3884
       device_release+0xd2/0x270 drivers/base/core.c:2640
       kobject_cleanup lib/kobject.c:689 [inline]
       kobject_release lib/kobject.c:720 [inline]
       kref_put include/linux/kref.h:65 [inline]
       kobject_put+0x1f7/0x640 lib/kobject.c:737
       put_device+0x1f/0x30 drivers/base/core.c:3884
       hci_conn_put include/net/bluetooth/hci_core.h:1690 [inline]
       l2cap_conn_free net/bluetooth/l2cap_core.c:1856 [inline]
       kref_put include/linux/kref.h:65 [inline]
       l2cap_conn_put net/bluetooth/l2cap_core.c:1869 [inline]
       l2cap_chan_destroy net/bluetooth/l2cap_core.c:494 [inline]
       kref_put include/linux/kref.h:65 [inline]
       l2cap_chan_put+0x352/0x3f0 net/bluetooth/l2cap_core.c:521
       l2cap_sock_release+0x1db/0x280 net/bluetooth/l2cap_sock.c:1533
       __sock_release net/socket.c:735 [inline]
       sock_release+0x91/0x1c0 net/socket.c:763
       rfcomm_session_del.isra.0+0x16b/0x250 net/bluetooth/rfcomm/core.c:782
       rfcomm_process_rx net/bluetooth/rfcomm/core.c:2086 [inline]
       rfcomm_process_sessions net/bluetooth/rfcomm/core.c:2171 [inline]
       rfcomm_run+0x6f6/0x5550 net/bluetooth/rfcomm/core.c:2261
       kthread+0x373/0x450 kernel/kthread.c:436
       ret_from_fork+0x730/0xd60 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

other info that might help us debug this:

Chain exists of:
  (wq_completion)hci0#2 --> hci_cb_list_lock --> rfcomm_mutex

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(rfcomm_mutex);
                               lock(hci_cb_list_lock);
                               lock(rfcomm_mutex);
  lock((wq_completion)hci0#2);

 *** DEADLOCK ***

locks held by krfcommd/3370: 1, last CPU#2:
 #0: ffffffff91f84880 (rfcomm_mutex){+.+.}-{4:4}, at: rfcomm_process_sessions net/bluetooth/rfcomm/core.c:2152 [inline]
 #0: ffffffff91f84880 (rfcomm_mutex){+.+.}-{4:4}, at: rfcomm_run+0x30b/0x5550 net/bluetooth/rfcomm/core.c:2261

stack backtrace:
CPU: 2 UID: 0 PID: 3370 Comm: krfcommd Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
 print_circular_bug.cold+0x178/0x1be kernel/locking/lockdep.c:2087
 check_noncircular+0x146/0x160 kernel/locking/lockdep.c:2219
 check_prev_add+0xeb/0xe60 kernel/locking/lockdep.c:3209
 check_prevs_add kernel/locking/lockdep.c:3328 [inline]
 validate_chain kernel/locking/lockdep.c:3952 [inline]
 __lock_acquire+0x1528/0x1f40 kernel/locking/lockdep.c:5288
 lock_acquire kernel/locking/lockdep.c:5942 [inline]
 lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5899
 touch_wq_lockdep_map+0xad/0x1c0 kernel/workqueue.c:4111
 __flush_workqueue+0x131/0x1200 kernel/workqueue.c:4153
 drain_workqueue+0x175/0x3b0 kernel/workqueue.c:4317
 destroy_workqueue+0xc3/0xa30 kernel/workqueue.c:6155
 hci_release_dev+0x116/0x630 net/bluetooth/hci_core.c:2728
 bt_host_release+0x6b/0xb0 net/bluetooth/hci_sysfs.c:100
 device_release+0xd2/0x270 drivers/base/core.c:2640
 kobject_cleanup lib/kobject.c:689 [inline]
 kobject_release lib/kobject.c:720 [inline]
 kref_put include/linux/kref.h:65 [inline]
 kobject_put+0x1f7/0x640 lib/kobject.c:737
 put_device+0x1f/0x30 drivers/base/core.c:3884
 device_release+0xd2/0x270 drivers/base/core.c:2640
 kobject_cleanup lib/kobject.c:689 [inline]
 kobject_release lib/kobject.c:720 [inline]
 kref_put include/linux/kref.h:65 [inline]
 kobject_put+0x1f7/0x640 lib/kobject.c:737
 put_device+0x1f/0x30 drivers/base/core.c:3884
 hci_conn_put include/net/bluetooth/hci_core.h:1690 [inline]
 l2cap_conn_free net/bluetooth/l2cap_core.c:1856 [inline]
 kref_put include/linux/kref.h:65 [inline]
 l2cap_conn_put net/bluetooth/l2cap_core.c:1869 [inline]
 l2cap_chan_destroy net/bluetooth/l2cap_core.c:494 [inline]
 kref_put include/linux/kref.h:65 [inline]
 l2cap_chan_put+0x352/0x3f0 net/bluetooth/l2cap_core.c:521
 l2cap_sock_release+0x1db/0x280 net/bluetooth/l2cap_sock.c:1533
 __sock_release net/socket.c:735 [inline]
 sock_release+0x91/0x1c0 net/socket.c:763
 rfcomm_session_del.isra.0+0x16b/0x250 net/bluetooth/rfcomm/core.c:782
 rfcomm_process_rx net/bluetooth/rfcomm/core.c:2086 [inline]
 rfcomm_process_sessions net/bluetooth/rfcomm/core.c:2171 [inline]
 rfcomm_run+0x6f6/0x5550 net/bluetooth/rfcomm/core.c:2261
 kthread+0x373/0x450 kernel/kthread.c:436
 ret_from_fork+0x730/0xd60 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>
All LE connection parameters were removed
hci0: Unregister MSFT extension
kobject: 'hci0': free name