hcon ffff888109d28000
hci2: conn ffff888109d28000
device: 'hci2:200': device_unregister
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Tainted: G             L     
------------------------------------------------------
kworker/u11:3/26142 is trying to acquire lock:
ffff8881012d4180 (&root->kernfs_rwsem){++++}-{4:4}, at: kernfs_remove_by_name_ns+0x4e/0x140

but task is already holding lock:
ffff8881012d42a0 (&root->kernfs_supers_rwsem){++++}-{4:4}, at: kernfs_remove_by_name_ns+0x3f/0x140

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #9 (&root->kernfs_supers_rwsem){++++}-{4:4}:
       down_read+0x4a/0x330
       kernfs_remove_by_name_ns+0x3f/0x140
       sysfs_remove_group+0x101/0x2e0
       topology_remove_dev+0x22/0x30
       cpuhp_invoke_callback+0x434/0x810
       _cpu_down+0x343/0x840
       cpu_device_down+0x82/0xc0
       device_offline+0x2d2/0x3c0
       online_store+0x123/0x1a0
       kernfs_fop_write_iter+0x3a4/0x540
       vfs_write+0x612/0xba0
       ksys_write+0x150/0x270
       do_syscall_64+0x166/0x520
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #8 (cpu_hotplug_lock){++++}-{0:0}:
       cpus_read_lock+0x42/0x160
       static_key_disable+0x12/0x20
       __inet_hash_connect+0x258f/0x25a0
       tcp_v4_connect+0xcee/0x1950
       __inet_stream_connect+0x258/0xe00
       inet_stream_connect+0x66/0xa0
       __sys_connect+0x316/0x450
       __x64_sys_connect+0x7a/0x90
       do_syscall_64+0x166/0x520
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #7 (sk_lock-AF_INET){+.+.}-{0:0}:
       lock_sock_nested+0x41/0x100
       inet_shutdown+0x6a/0x390
       nbd_mark_nsock_dead+0x2cb/0x550
       recv_work+0x1cee/0x1e10
       process_scheduled_works+0xc3d/0x1630
       worker_thread+0xa47/0xfb0
       kthread+0x38b/0x480
       ret_from_fork+0x514/0xb70
       ret_from_fork_asm+0x1a/0x30

-> #6 (&nsock->tx_lock){+.+.}-{4:4}:
       __mutex_lock+0x19d/0x1550
       nbd_queue_rq+0x373/0xff0
       blk_mq_dispatch_rq_list+0x499/0x1990
       __blk_mq_sched_dispatch_requests+0xd36/0x1580
       blk_mq_sched_dispatch_requests+0xd7/0x190
       blk_mq_run_work_fn+0x16c/0x300
       process_scheduled_works+0xc3d/0x1630
       worker_thread+0xa47/0xfb0
       kthread+0x38b/0x480
       ret_from_fork+0x514/0xb70
       ret_from_fork_asm+0x1a/0x30

-> #5 (&cmd->lock){+.+.}-{4:4}:
       __mutex_lock+0x19d/0x1550
       nbd_queue_rq+0xc1/0xff0
       blk_mq_dispatch_rq_list+0x499/0x1990
       __blk_mq_sched_dispatch_requests+0xd36/0x1580
       blk_mq_sched_dispatch_requests+0xd7/0x190
       blk_mq_run_work_fn+0x16c/0x300
       process_scheduled_works+0xc3d/0x1630
       worker_thread+0xa47/0xfb0
       kthread+0x38b/0x480
       ret_from_fork+0x514/0xb70
       ret_from_fork_asm+0x1a/0x30

-> #4 (set->srcu){.+.+}-{0:0}:
       __synchronize_srcu+0xc9/0x2f0
       elevator_switch+0x1e8/0x7b0
       elevator_change+0x2fa/0x480
       elevator_set_default+0x375/0x440
       blk_register_queue+0x3f3/0x4e0
       __add_disk+0x6cb/0xe30
       add_disk_fwnode+0x100/0x3a0
       nbd_dev_add+0x733/0xb60
       nbd_init+0x168/0x1f0
       do_one_initcall+0x250/0x870
       do_initcall_level+0x10a/0x1a0
       do_initcalls+0x59/0xa0
       kernel_init_freeable+0x29d/0x3e0
       kernel_init+0x22/0x1d0
       ret_from_fork+0x514/0xb70
       ret_from_fork_asm+0x1a/0x30

-> #3 (&q->elevator_lock){+.+.}-{4:4}:
       __mutex_lock+0x19d/0x1550
       elevator_change+0x1af/0x480
       elv_iosched_store+0x504/0x630
       queue_attr_store+0x207/0x2b0
       kernfs_fop_write_iter+0x3a4/0x540
       vfs_write+0x612/0xba0
       ksys_write+0x150/0x270
       do_syscall_64+0x166/0x520
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #2 (&q->q_usage_counter(io)#66){++++}-{0:0}:
       blk_alloc_queue+0x544/0x690
       __blk_mq_alloc_disk+0x194/0x390
       null_add_dev+0xe82/0x1d70
       null_init+0x1e3/0x390
       do_one_initcall+0x250/0x870
       do_initcall_level+0x10a/0x1a0
       do_initcalls+0x59/0xa0
       kernel_init_freeable+0x29d/0x3e0
       kernel_init+0x22/0x1d0
       ret_from_fork+0x514/0xb70
       ret_from_fork_asm+0x1a/0x30

-> #1 (fs_reclaim){+.+.}-{0:0}:
       fs_reclaim_acquire+0x71/0x100
       kmem_cache_alloc_lru_noprof+0x65/0x5f0
       alloc_inode+0xb8/0x1b0
       iget_locked+0x131/0x6a0
       kernfs_get_inode+0x4f/0x770
       kernfs_get_tree+0x5cd/0x980
       vfs_get_tree+0x92/0x2a0
       do_new_mount+0x319/0xdc0
       __se_sys_mount+0x31d/0x420
       do_syscall_64+0x166/0x520
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (&root->kernfs_rwsem){++++}-{4:4}:
       __lock_acquire+0x1520/0x2cf0
       lock_acquire+0x106/0x350
       down_write+0x96/0x200
       kernfs_remove_by_name_ns+0x4e/0x140
       sysfs_unmerge_group+0xd3/0x140
       dpm_sysfs_remove+0x5f/0xd0
       device_del+0x250/0x8f0
       device_unregister+0x21/0xf0
       hci_conn_del+0xc3d/0x1200
       hci_abort_conn_sync+0xdd0/0x1190
       hci_cmd_sync_work+0x20b/0x3f0
       process_scheduled_works+0xc3d/0x1630
       worker_thread+0xa47/0xfb0
       kthread+0x38b/0x480
       ret_from_fork+0x514/0xb70
       ret_from_fork_asm+0x1a/0x30

other info that might help us debug this:

Chain exists of:
  &root->kernfs_rwsem --> cpu_hotplug_lock --> &root->kernfs_supers_rwsem

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  rlock(&root->kernfs_supers_rwsem);
                               lock(cpu_hotplug_lock);
                               lock(&root->kernfs_supers_rwsem);
  lock(&root->kernfs_rwsem);

 *** DEADLOCK ***

locks held by kworker/u11:3/26142: 5, last CPU#0:
 #0: ffff888020962140 ((wq_completion)hci2){+.+.}-{0:0}, at: process_scheduled_works+0x97a/0x1630
 #1: ffffc90004c9fc40 ((work_completion)(&hdev->cmd_sync_work)){+.+.}-{0:0}, at: process_scheduled_works+0x97a/0x1630
 #2: ffff888112ff4ea0 (&hdev->req_lock){+.+.}-{4:4}, at: hci_cmd_sync_work+0x1cb/0x3f0
 #3: ffff888112ff40b8 (&hdev->lock){+.+.}-{4:4}, at: hci_abort_conn_sync+0xa6f/0x1190
 #4: ffff8881012d42a0 (&root->kernfs_supers_rwsem){++++}-{4:4}, at: kernfs_remove_by_name_ns+0x3f/0x140

stack backtrace:
CPU: 0 UID: 0 PID: 26142 Comm: kworker/u11:3 Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
Workqueue: hci2 hci_cmd_sync_work
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150
 print_circular_bug+0x2e1/0x300
 check_noncircular+0x12e/0x150
 __lock_acquire+0x1520/0x2cf0
 lock_acquire+0x106/0x350
 down_write+0x96/0x200
 kernfs_remove_by_name_ns+0x4e/0x140
 sysfs_unmerge_group+0xd3/0x140
 dpm_sysfs_remove+0x5f/0xd0
 device_del+0x250/0x8f0
 device_unregister+0x21/0xf0
 hci_conn_del+0xc3d/0x1200
 hci_abort_conn_sync+0xdd0/0x1190
 hci_cmd_sync_work+0x20b/0x3f0
 process_scheduled_works+0xc3d/0x1630
 worker_thread+0xa47/0xfb0
 kthread+0x38b/0x480
 ret_from_fork+0x514/0xb70
 ret_from_fork_asm+0x1a/0x30
 </TASK>
kernfs runtime_status: removing
kernfs control: removing
kernfs runtime_suspended_time: removing
kernfs runtime_active_time: removing
kernfs autosuspend_delay_ms: removing
kernfs power: removing
kernfs device: removing
kernfs subsystem: removing
kernfs hci2:200: removing
kernfs uevent: removing
PM: Removing info for No Bus:hci2:200
kobject: 'hci2:200' (ffff888109d28cf0): kobject_uevent_env
kobject: 'hci2:200' (ffff888109d28cf0): fill_kobj_path: path = '/devices/virtual/bluetooth/hci2/hci2:200'
kernfs hci2:200: removing
hci2 orig refcnt 10
kobject: 'hci2:200' (ffff888109d28cf0): kobject_cleanup, parent 0000000000000000
kobject: 'hci2:200' (ffff888109d28cf0): calling ktype release
kobject: 'hci2:200': free name
