syzbot

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
kworker/0:4/5310 is trying to acquire lock:
ffff8880422d4338 (&conn->lock#2){+.+.}-{4:4}, at: l2cap_info_timeout+0x60/0xa0 net/bluetooth/l2cap_core.c:1668

but task is already holding lock:
ffffc9000f4d7ba0 ((work_completion)(&(&conn->info_timer)->work)){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3239 [inline]
ffffc9000f4d7ba0 ((work_completion)(&(&conn->info_timer)->work)){+.+.}-{0:0}, at: process_scheduled_works+0x9ef/0x17b0 kernel/workqueue.c:3346

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:3951 [inline]
       start_flush_work kernel/workqueue.c:4205 [inline]
       __flush_work+0x6b8/0xbc0 kernel/workqueue.c:4237
       __cancel_work_sync+0xbe/0x110 kernel/workqueue.c:4393
       l2cap_conn_del+0x4f0/0x680 net/bluetooth/l2cap_core.c:1796
       l2cap_connect_cfm+0x11d/0x1040 net/bluetooth/l2cap_core.c:7259
       hci_connect_cfm include/net/bluetooth/hci_core.h:2106 [inline]
       hci_conn_failed+0x1ce/0x310 net/bluetooth/hci_conn.c:1312
       hci_abort_conn_sync+0x658/0xe30 net/bluetooth/hci_sync.c:5698
       hci_disconnect_all_sync+0x1b5/0x350 net/bluetooth/hci_sync.c:5721
       hci_suspend_sync+0x3fc/0xc60 net/bluetooth/hci_sync.c:6197
       hci_suspend_dev+0x28d/0x4d0 net/bluetooth/hci_core.c:2849
       hci_suspend_notifier+0xf2/0x290 net/bluetooth/hci_core.c:2420
       notifier_call_chain+0x1b6/0x3e0 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:103
       snapshot_open+0x19c/0x280 kernel/power/user.c:77
       misc_open+0x2d5/0x350 drivers/char/misc.c:163
       chrdev_open+0x4cc/0x5e0 fs/char_dev.c:414
       do_dentry_open+0x953/0x13f0 fs/open.c:965
       vfs_open+0x3b/0x340 fs/open.c:1097
       do_open fs/namei.c:3975 [inline]
       path_openat+0x2ee5/0x3830 fs/namei.c:4134
       do_filp_open+0x1fa/0x410 fs/namei.c:4161
       do_sys_openat2+0x121/0x1c0 fs/open.c:1437
       do_sys_open fs/open.c:1452 [inline]
       __do_sys_openat fs/open.c:1468 [inline]
       __se_sys_openat fs/open.c:1463 [inline]
       __x64_sys_openat+0x138/0x170 fs/open.c:1463
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0xfa0 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:3263 [inline]
       process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3346
       worker_thread+0x8a0/0xda0 kernel/workqueue.c:3427
       kthread+0x711/0x8a0 kernel/kthread.c:463
       ret_from_fork+0x4bc/0x870 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/0:4/5310:
 #0: ffff88801a469548 ((wq_completion)events){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3238 [inline]
 #0: ffff88801a469548 ((wq_completion)events){+.+.}-{0:0}, at: process_scheduled_works+0x9b4/0x17b0 kernel/workqueue.c:3346
 #1: ffffc9000f4d7ba0 ((work_completion)(&(&conn->info_timer)->work)){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3239 [inline]
 #1: ffffc9000f4d7ba0 ((work_completion)(&(&conn->info_timer)->work)){+.+.}-{0:0}, at: process_scheduled_works+0x9ef/0x17b0 kernel/workqueue.c:3346

stack backtrace:
CPU: 0 UID: 0 PID: 5310 Comm: kworker/0:4 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:3263 [inline]
 process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3346
 worker_thread+0x8a0/0xda0 kernel/workqueue.c:3427
 kthread+0x711/0x8a0 kernel/kthread.c:463
 ret_from_fork+0x4bc/0x870 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>