syzbot

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
kworker/0:5/5354 is trying to acquire lock:
ffff888052051b38 (&conn->lock#2){+.+.}-{4:4}, at: l2cap_info_timeout+0x60/0xa0 net/bluetooth/l2cap_core.c:1668

but task is already holding lock:
ffffc9000d4efbc0 ((work_completion)(&(&conn->info_timer)->work)){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3212 [inline]
ffffc9000d4efbc0 ((work_completion)(&(&conn->info_timer)->work)){+.+.}-{0:0}, at: process_scheduled_works+0x9ef/0x17b0 kernel/workqueue.c:3319

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}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
       touch_work_lockdep_map kernel/workqueue.c:3922 [inline]
       start_flush_work kernel/workqueue.c:4176 [inline]
       __flush_work+0x6b8/0xbc0 kernel/workqueue.c:4208
       __cancel_work_sync+0xbe/0x110 kernel/workqueue.c:4364
       l2cap_conn_del+0x4f0/0x680 net/bluetooth/l2cap_core.c:1796
       hci_disconn_cfm include/net/bluetooth/hci_core.h:2097 [inline]
       hci_conn_hash_flush+0x10a/0x230 net/bluetooth/hci_conn.c:2599
       hci_dev_close_sync+0xaef/0x1330 net/bluetooth/hci_sync.c:5294
       hci_dev_do_close net/bluetooth/hci_core.c:501 [inline]
       hci_dev_close+0x108/0x200 net/bluetooth/hci_core.c:526
       sock_do_ioctl+0xd9/0x300 net/socket.c:1238
       sock_ioctl+0x576/0x790 net/socket.c:1359
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:598 [inline]
       __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:584
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0x3b0 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+0xb9b/0x2140 kernel/locking/lockdep.c:3908
       __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5237
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
       __mutex_lock_common kernel/locking/mutex.c:598 [inline]
       __mutex_lock+0x187/0x1350 kernel/locking/mutex.c:760
       l2cap_info_timeout+0x60/0xa0 net/bluetooth/l2cap_core.c:1668
       process_one_work kernel/workqueue.c:3236 [inline]
       process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3319
       worker_thread+0x8a0/0xda0 kernel/workqueue.c:3400
       kthread+0x70e/0x8a0 kernel/kthread.c:463
       ret_from_fork+0x3fc/0x770 arch/x86/kernel/process.c:148
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

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/0:5/5354:
 #0: ffff88801a474d48 ((wq_completion)events){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3211 [inline]
 #0: ffff88801a474d48 ((wq_completion)events){+.+.}-{0:0}, at: process_scheduled_works+0x9b4/0x17b0 kernel/workqueue.c:3319
 #1: ffffc9000d4efbc0 ((work_completion)(&(&conn->info_timer)->work)){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3212 [inline]
 #1: ffffc9000d4efbc0 ((work_completion)(&(&conn->info_timer)->work)){+.+.}-{0:0}, at: process_scheduled_works+0x9ef/0x17b0 kernel/workqueue.c:3319

stack backtrace:
CPU: 0 UID: 0 PID: 5354 Comm: kworker/0:5 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+0x2ee/0x310 kernel/locking/lockdep.c:2043
 check_noncircular+0x134/0x160 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+0xb9b/0x2140 kernel/locking/lockdep.c:3908
 __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5237
 lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
 __mutex_lock_common kernel/locking/mutex.c:598 [inline]
 __mutex_lock+0x187/0x1350 kernel/locking/mutex.c:760
 l2cap_info_timeout+0x60/0xa0 net/bluetooth/l2cap_core.c:1668
 process_one_work kernel/workqueue.c:3236 [inline]
 process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3319
 worker_thread+0x8a0/0xda0 kernel/workqueue.c:3400
 kthread+0x70e/0x8a0 kernel/kthread.c:463
 ret_from_fork+0x3fc/0x770 arch/x86/kernel/process.c:148
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>