======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
kworker/0:1/11 is trying to acquire lock:
ffff88804186d338 (&conn->lock#2){+.+.}-{4:4}, at: l2cap_info_timeout+0x60/0xa0 net/bluetooth/l2cap_core.c:1669

but task is already holding lock:
ffffc900001d7b80 ((work_completion)(&(&conn->info_timer)->work)){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3233 [inline]
ffffc900001d7b80 ((work_completion)(&(&conn->info_timer)->work)){+.+.}-{0:0}, at: process_scheduled_works+0x9ef/0x1770 kernel/workqueue.c:3340

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 ((work_completion)(&(&conn->info_timer)->work)){+.+.}-{0:0}:
       touch_work_lockdep_map kernel/workqueue.c:3955 [inline]
       start_flush_work kernel/workqueue.c:4209 [inline]
       __flush_work+0x6b8/0xbc0 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_do_reset net/bluetooth/hci_core.c:566 [inline]
       hci_dev_reset+0x41c/0x6e0 net/bluetooth/hci_core.c:610
       sock_do_ioctl+0xdc/0x300 net/socket.c:1254
       sock_ioctl+0x576/0x790 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+0xfa/0xf80 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (&conn->lock#2){+.+.}-{4:4}:
       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+0x15a6/0x2cf0 kernel/locking/lockdep.c:5237
       lock_acquire+0x117/0x340 kernel/locking/lockdep.c:5868
       __mutex_lock_common kernel/locking/mutex.c:614 [inline]
       __mutex_lock+0x187/0x1350 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+0xad1/0x1770 kernel/workqueue.c:3340
       worker_thread+0x8a0/0xda0 kernel/workqueue.c:3421
       kthread+0x711/0x8a0 kernel/kthread.c:463
       ret_from_fork+0x599/0xb30 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246

other info that might help us debug this:

 Possible unsafe locking scenario:

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

 *** DEADLOCK ***

2 locks held by kworker/0:1/11:
 #0: ffff88801a467548 ((wq_completion)events){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3232 [inline]
 #0: ffff88801a467548 ((wq_completion)events){+.+.}-{0:0}, at: process_scheduled_works+0x9b4/0x1770 kernel/workqueue.c:3340
 #1: ffffc900001d7b80 ((work_completion)(&(&conn->info_timer)->work)){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3233 [inline]
 #1: ffffc900001d7b80 ((work_completion)(&(&conn->info_timer)->work)){+.+.}-{0:0}, at: process_scheduled_works+0x9ef/0x1770 kernel/workqueue.c:3340

stack backtrace:
CPU: 0 UID: 0 PID: 11 Comm: kworker/0:1 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
Workqueue: events l2cap_info_timeout
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 print_circular_bug+0x2e2/0x300 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+0x15a6/0x2cf0 kernel/locking/lockdep.c:5237
 lock_acquire+0x117/0x340 kernel/locking/lockdep.c:5868
 __mutex_lock_common kernel/locking/mutex.c:614 [inline]
 __mutex_lock+0x187/0x1350 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+0xad1/0x1770 kernel/workqueue.c:3340
 worker_thread+0x8a0/0xda0 kernel/workqueue.c:3421
 kthread+0x711/0x8a0 kernel/kthread.c:463
 ret_from_fork+0x599/0xb30 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246
 </TASK>