======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.0.0/5321 is trying to acquire lock:
ffff888012378040 ((work_completion)(&(&conn->info_timer)->work)){+.+.}-{0:0}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline]
ffff888012378040 ((work_completion)(&(&conn->info_timer)->work)){+.+.}-{0:0}, at: rcu_read_lock include/linux/rcupdate.h:867 [inline]
ffff888012378040 ((work_completion)(&(&conn->info_timer)->work)){+.+.}-{0:0}, at: start_flush_work kernel/workqueue.c:4183 [inline]
ffff888012378040 ((work_completion)(&(&conn->info_timer)->work)){+.+.}-{0:0}, at: __flush_work+0x100/0xc50 kernel/workqueue.c:4241

but task is already holding lock:
ffff888012378338 (&conn->lock#2){+.+.}-{4:4}, at: l2cap_conn_del+0x7b/0x5b0 net/bluetooth/l2cap_core.c:1763

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (&conn->lock#2){+.+.}-{4:4}:
       __mutex_lock_common kernel/locking/mutex.c:614 [inline]
       __mutex_lock+0x19f/0x1300 kernel/locking/mutex.c:776
       l2cap_info_timeout+0x60/0xa0 net/bluetooth/l2cap_core.c:1669
       process_one_work kernel/workqueue.c:3257 [inline]
       process_scheduled_works+0xaec/0x17a0 kernel/workqueue.c:3340
       worker_thread+0xda6/0x1360 kernel/workqueue.c:3421
       kthread+0x726/0x8b0 kernel/kthread.c:463
       ret_from_fork+0x51b/0xa40 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246

-> #0 ((work_completion)(&(&conn->info_timer)->work)){+.+.}-{0:0}:
       check_prev_add kernel/locking/lockdep.c:3165 [inline]
       check_prevs_add kernel/locking/lockdep.c:3284 [inline]
       validate_chain kernel/locking/lockdep.c:3908 [inline]
       __lock_acquire+0x15a5/0x2cf0 kernel/locking/lockdep.c:5237
       lock_acquire+0x106/0x330 kernel/locking/lockdep.c:5868
       touch_work_lockdep_map kernel/workqueue.c:3955 [inline]
       start_flush_work kernel/workqueue.c:4209 [inline]
       __flush_work+0x700/0xc50 kernel/workqueue.c:4241
       __cancel_work_sync+0xbe/0x110 kernel/workqueue.c:4397
       l2cap_conn_del+0x402/0x5b0 net/bluetooth/l2cap_core.c:1797
       hci_disconn_cfm include/net/bluetooth/hci_core.h:2146 [inline]
       hci_conn_hash_flush+0x10d/0x260 net/bluetooth/hci_conn.c:2637
       hci_dev_close_sync+0x821/0x10e0 net/bluetooth/hci_sync.c:5327
       hci_dev_do_close net/bluetooth/hci_core.c:501 [inline]
       hci_dev_close+0x108/0x260 net/bluetooth/hci_core.c:526
       sock_do_ioctl+0x101/0x320 net/socket.c:1254
       sock_ioctl+0x5c6/0x7f0 net/socket.c:1375
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:597 [inline]
       __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xe2/0xf80 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&conn->lock#2);
                               lock((work_completion)(&(&conn->info_timer)->work));
                               lock(&conn->lock#2);
  lock((work_completion)(&(&conn->info_timer)->work));

 *** DEADLOCK ***

5 locks held by syz.0.0/5321:
 #0: ffff8880126e4ec0 (&hdev->req_lock){+.+.}-{4:4}, at: hci_dev_do_close net/bluetooth/hci_core.c:499 [inline]
 #0: ffff8880126e4ec0 (&hdev->req_lock){+.+.}-{4:4}, at: hci_dev_close+0x100/0x260 net/bluetooth/hci_core.c:526
 #1: ffff8880126e40c0 (&hdev->lock){+.+.}-{4:4}, at: hci_dev_close_sync+0x640/0x10e0 net/bluetooth/hci_sync.c:5315
 #2: ffffffff8fb3ad68 (hci_cb_list_lock){+.+.}-{4:4}, at: hci_disconn_cfm include/net/bluetooth/hci_core.h:2143 [inline]
 #2: ffffffff8fb3ad68 (hci_cb_list_lock){+.+.}-{4:4}, at: hci_conn_hash_flush+0xa1/0x260 net/bluetooth/hci_conn.c:2637
 #3: ffff888012378338 (&conn->lock#2){+.+.}-{4:4}, at: l2cap_conn_del+0x7b/0x5b0 net/bluetooth/l2cap_core.c:1763
 #4: ffffffff8e55a360 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline]
 #4: ffffffff8e55a360 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:867 [inline]
 #4: ffffffff8e55a360 (rcu_read_lock){....}-{1:3}, at: start_flush_work kernel/workqueue.c:4183 [inline]
 #4: ffffffff8e55a360 (rcu_read_lock){....}-{1:3}, at: __flush_work+0x100/0xc50 kernel/workqueue.c:4241

stack backtrace:
CPU: 0 UID: 0 PID: 5321 Comm: syz.0.0 Not tainted syzkaller #0 PREEMPT(full) 
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_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_circular_bug+0x2e1/0x300 kernel/locking/lockdep.c:2043
 check_noncircular+0x12e/0x150 kernel/locking/lockdep.c:2175
 check_prev_add kernel/locking/lockdep.c:3165 [inline]
 check_prevs_add kernel/locking/lockdep.c:3284 [inline]
 validate_chain kernel/locking/lockdep.c:3908 [inline]
 __lock_acquire+0x15a5/0x2cf0 kernel/locking/lockdep.c:5237
 lock_acquire+0x106/0x330 kernel/locking/lockdep.c:5868
 touch_work_lockdep_map kernel/workqueue.c:3955 [inline]
 start_flush_work kernel/workqueue.c:4209 [inline]
 __flush_work+0x700/0xc50 kernel/workqueue.c:4241
 __cancel_work_sync+0xbe/0x110 kernel/workqueue.c:4397
 l2cap_conn_del+0x402/0x5b0 net/bluetooth/l2cap_core.c:1797
 hci_disconn_cfm include/net/bluetooth/hci_core.h:2146 [inline]
 hci_conn_hash_flush+0x10d/0x260 net/bluetooth/hci_conn.c:2637
 hci_dev_close_sync+0x821/0x10e0 net/bluetooth/hci_sync.c:5327
 hci_dev_do_close net/bluetooth/hci_core.c:501 [inline]
 hci_dev_close+0x108/0x260 net/bluetooth/hci_core.c:526
 sock_do_ioctl+0x101/0x320 net/socket.c:1254
 sock_ioctl+0x5c6/0x7f0 net/socket.c:1375
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xe2/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f936dd9aeb9
Code: ff 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 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f936ece9028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f936e015fa0 RCX: 00007f936dd9aeb9
RDX: 0000000000000000 RSI: 00000000400448ca RDI: 0000000000000006
RBP: 00007f936de08c1f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f936e016038 R14: 00007f936e015fa0 R15: 00007fff8a5cf4d8
 </TASK>