syzbot

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
kworker/0:1/10 is trying to acquire lock:
ffff8880429d2af8 (&conn->lock#2){+.+.}-{4:4}, at: l2cap_info_timeout+0x60/0xa0 net/bluetooth/l2cap_core.c:1661

but task is already holding lock:
ffffc9000023fc40 ((work_completion)(&(&conn->info_timer)->work)){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3251 [inline]
ffffc9000023fc40 ((work_completion)(&(&conn->info_timer)->work)){+.+.}-{0:0}, at: process_scheduled_works+0xa25/0x1830 kernel/workqueue.c:3358

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:4005 [inline]
       start_flush_work kernel/workqueue.c:4259 [inline]
       __flush_work+0x700/0xc50 kernel/workqueue.c:4291
       __cancel_work_sync+0xbe/0x110 kernel/workqueue.c:4447
       l2cap_conn_del+0x40f/0x5c0 net/bluetooth/l2cap_core.c:1791
       l2cap_connect_cfm+0x12b/0x1390 net/bluetooth/l2cap_core.c:7323
       hci_connect_cfm include/net/bluetooth/hci_core.h:2139 [inline]
       hci_conn_failed+0x1ce/0x340 net/bluetooth/hci_conn.c:1342
       hci_abort_conn_sync+0xdd0/0x1190 net/bluetooth/hci_sync.c:5753
       hci_disconnect_all_sync+0x1b5/0x350 net/bluetooth/hci_sync.c:5776
       hci_suspend_sync+0x417/0xd20 net/bluetooth/hci_sync.c:6252
       hci_suspend_dev+0x28d/0x540 net/bluetooth/hci_core.c:2850
       hci_suspend_notifier+0xf2/0x2f0 net/bluetooth/hci_core.c:2421
       notifier_call_chain+0x1be/0x400 kernel/notifier.c:85
       notifier_call_chain_robust kernel/notifier.c:120 [inline]
       blocking_notifier_call_chain_robust+0x85/0x100 kernel/notifier.c:345
       pm_notifier_call_chain_robust+0x2c/0x60 kernel/power/main.c:172
       snapshot_open+0x19c/0x280 kernel/power/user.c:77
       misc_open+0x2d5/0x350 drivers/char/misc.c:163
       chrdev_open+0x4cd/0x5e0 fs/char_dev.c:411
       do_dentry_open+0x785/0x14e0 fs/open.c:949
       vfs_open+0x3b/0x340 fs/open.c:1081
       do_open fs/namei.c:4671 [inline]
       path_openat+0x2e08/0x3860 fs/namei.c:4830
       do_file_open+0x23e/0x4a0 fs/namei.c:4859
       do_sys_openat2+0x113/0x200 fs/open.c:1366
       do_sys_open fs/open.c:1372 [inline]
       __do_sys_openat fs/open.c:1388 [inline]
       __se_sys_openat fs/open.c:1383 [inline]
       __x64_sys_openat+0x138/0x170 fs/open.c:1383
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x14d/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+0x15a5/0x2cf0 kernel/locking/lockdep.c:5237
       lock_acquire+0xf0/0x2e0 kernel/locking/lockdep.c:5868
       __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:1661
       process_one_work kernel/workqueue.c:3275 [inline]
       process_scheduled_works+0xb02/0x1830 kernel/workqueue.c:3358
       worker_thread+0xa50/0xfc0 kernel/workqueue.c:3439
       kthread+0x388/0x470 kernel/kthread.c:436
       ret_from_fork+0x51e/0xb90 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:

 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/0:1/10:
 #0: ffff88801aca6948 ((wq_completion)events){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3250 [inline]
 #0: ffff88801aca6948 ((wq_completion)events){+.+.}-{0:0}, at: process_scheduled_works+0x9ea/0x1830 kernel/workqueue.c:3358
 #1: ffffc9000023fc40 ((work_completion)(&(&conn->info_timer)->work)){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3251 [inline]
 #1: ffffc9000023fc40 ((work_completion)(&(&conn->info_timer)->work)){+.+.}-{0:0}, at: process_scheduled_works+0xa25/0x1830 kernel/workqueue.c:3358

stack backtrace:
CPU: 0 UID: 0 PID: 10 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 04/01/2014
Workqueue: events l2cap_info_timeout
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+0xf0/0x2e0 kernel/locking/lockdep.c:5868
 __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:1661
 process_one_work kernel/workqueue.c:3275 [inline]
 process_scheduled_works+0xb02/0x1830 kernel/workqueue.c:3358
 worker_thread+0xa50/0xfc0 kernel/workqueue.c:3439
 kthread+0x388/0x470 kernel/kthread.c:436
 ret_from_fork+0x51e/0xb90 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>