======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Tainted: G             L     
------------------------------------------------------
kworker/u34:0/27988 is trying to acquire lock:
ffff88801d6c7210 (&root->kernfs_iattr_rwsem){++++}-{4:4}, at: kernfs_link_sibling+0x555/0x850 fs/kernfs/dir.c:411

but task is already holding lock:
ffff88801d6c7180 (&root->kernfs_rwsem){++++}-{4:4}, at: kernfs_add_one+0x38/0xaa0 fs/kernfs/dir.c:825

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #9 (&root->kernfs_rwsem){++++}-{4:4}:
       lock_acquire kernel/locking/lockdep.c:5942 [inline]
       lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5899
       down_write+0x8b/0x1f0 kernel/locking/rwsem.c:1631
       kernfs_add_one+0x38/0xaa0 fs/kernfs/dir.c:825
       kernfs_create_dir_ns+0x157/0x2b0 fs/kernfs/dir.c:1130
       internal_create_group+0x36f/0xfb0 fs/sysfs/group.c:176
       cpuhp_invoke_callback+0x3b4/0x9a0 kernel/cpu.c:194
       cpuhp_issue_call+0x1b8/0x970 kernel/cpu.c:2354
       __cpuhp_setup_state_cpuslocked+0x431/0x880 kernel/cpu.c:2507
       __cpuhp_setup_state+0xf7/0x2f0 kernel/cpu.c:2536
       do_one_initcall+0x11c/0x6f0 init/main.c:1362
       do_initcall_level init/main.c:1424 [inline]
       do_initcalls init/main.c:1440 [inline]
       do_basic_setup init/main.c:1460 [inline]
       kernel_init_freeable+0x6ea/0x7b0 init/main.c:1675
       kernel_init+0x21/0x1e0 init/main.c:1565
       ret_from_fork+0x730/0xd60 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #8 (cpuhp_state_mutex){+.+.}-{4:4}:

-> #7 (cpu_hotplug_lock){++++}-{0:0}:
       lock_acquire kernel/locking/lockdep.c:5942 [inline]
       lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5899
       percpu_down_read_internal include/linux/percpu-rwsem.h:53 [inline]
       percpu_down_read include/linux/percpu-rwsem.h:77 [inline]
       cpus_read_lock+0x42/0x170 kernel/cpu.c:490
       static_key_slow_inc+0x12/0x30 kernel/jump_label.c:190
       nbd_genl_reconnect_sock_cb+0x39f/0x990 drivers/block/nbd.c:1377
       nbd_genl_foreach_sock+0x2ab/0x3e0 drivers/block/nbd.c:2152
       nbd_genl_reconfigure+0x861/0xde0 drivers/block/nbd.c:2477
       genl_family_rcv_msg_doit+0x214/0x300 net/netlink/genetlink.c:1114
       genl_family_rcv_msg net/netlink/genetlink.c:1194 [inline]
       genl_rcv_msg+0x560/0x800 net/netlink/genetlink.c:1209
       netlink_rcv_skb+0x159/0x420 net/netlink/af_netlink.c:2575
       genl_rcv+0x28/0x40 net/netlink/genetlink.c:1218
       netlink_unicast_kernel net/netlink/af_netlink.c:1338 [inline]
       netlink_unicast+0x585/0x850 net/netlink/af_netlink.c:1364
       netlink_sendmsg+0x8b0/0xda0 net/netlink/af_netlink.c:1919
       sock_sendmsg_nosec net/socket.c:800 [inline]
       __sock_sendmsg net/socket.c:815 [inline]
       ____sys_sendmsg+0xa4d/0xbe0 net/socket.c:2713
       ___sys_sendmsg+0x190/0x1e0 net/socket.c:2767
       __sys_sendmsg+0x160/0x210 net/socket.c:2799
       do_syscall_32_irqs_on arch/x86/entry/syscall_32.c:79 [inline]
       __do_fast_syscall_32+0x13a/0x8b0 arch/x86/entry/syscall_32.c:291
       do_fast_syscall_32+0x32/0x70 arch/x86/entry/syscall_32.c:316
       entry_SYSENTER_compat_after_hwframe+0x84/0x8e

-> #6 (&nsock->tx_lock){+.+.}-{4:4}:
       lock_acquire kernel/locking/lockdep.c:5942 [inline]
       lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5899
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x1a4/0x1bd0 kernel/locking/mutex.c:821
       nbd_handle_cmd drivers/block/nbd.c:1143 [inline]
       nbd_queue_rq+0x42d/0xfa0 drivers/block/nbd.c:1207
       blk_mq_dispatch_rq_list+0x428/0x1e60 block/blk-mq.c:2117
       __blk_mq_do_dispatch_sched block/blk-mq-sched.c:168 [inline]
       blk_mq_do_dispatch_sched block/blk-mq-sched.c:182 [inline]
       __blk_mq_sched_dispatch_requests+0xcea/0x1620 block/blk-mq-sched.c:307
       blk_mq_sched_dispatch_requests+0xd7/0x1c0 block/blk-mq-sched.c:329
       blk_mq_run_work_fn+0x135/0x380 block/blk-mq.c:2531
       process_one_work+0xac7/0x1b10 kernel/workqueue.c:3396
       process_scheduled_works kernel/workqueue.c:3479 [inline]
       worker_thread+0x5ef/0xe50 kernel/workqueue.c:3560
       kthread+0x373/0x450 kernel/kthread.c:436
       ret_from_fork+0x730/0xd60 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #5 (&cmd->lock){+.+.}-{4:4}:
       lock_acquire kernel/locking/lockdep.c:5942 [inline]
       lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5899
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x1a4/0x1bd0 kernel/locking/mutex.c:821
       nbd_queue_rq+0xba/0xfa0 drivers/block/nbd.c:1199
       blk_mq_dispatch_rq_list+0x428/0x1e60 block/blk-mq.c:2117
       __blk_mq_do_dispatch_sched block/blk-mq-sched.c:168 [inline]
       blk_mq_do_dispatch_sched block/blk-mq-sched.c:182 [inline]
       __blk_mq_sched_dispatch_requests+0xcea/0x1620 block/blk-mq-sched.c:307
       blk_mq_sched_dispatch_requests+0xd7/0x1c0 block/blk-mq-sched.c:329
       blk_mq_run_work_fn+0x135/0x380 block/blk-mq.c:2531
       process_one_work+0xac7/0x1b10 kernel/workqueue.c:3396
       process_scheduled_works kernel/workqueue.c:3479 [inline]
       worker_thread+0x5ef/0xe50 kernel/workqueue.c:3560
       kthread+0x373/0x450 kernel/kthread.c:436
       ret_from_fork+0x730/0xd60 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #4 (set->srcu){.+.+}-{0:0}:
       lock_sync kernel/locking/lockdep.c:5991 [inline]
       lock_sync+0xb5/0x120 kernel/locking/lockdep.c:5979
       srcu_lock_sync include/linux/srcu.h:210 [inline]
       __synchronize_srcu+0xa2/0x300 kernel/rcu/srcutree.c:1462
       blk_mq_wait_quiesce_done block/blk-mq.c:284 [inline]
       blk_mq_wait_quiesce_done block/blk-mq.c:281 [inline]
       blk_mq_quiesce_queue block/blk-mq.c:304 [inline]
       blk_mq_quiesce_queue+0x149/0x1c0 block/blk-mq.c:299
       elevator_switch+0x17b/0x7e0 block/elevator.c:576
       elevator_change+0x352/0x530 block/elevator.c:681
       elevator_set_default+0x29e/0x360 block/elevator.c:754
       blk_register_queue+0x48e/0x630 block/blk-sysfs.c:992
       __add_disk+0x7dd/0xf10 block/genhd.c:531
       add_disk_fwnode+0x118/0x480 block/genhd.c:600
       add_disk include/linux/blkdev.h:798 [inline]
       nbd_dev_add+0x779/0xb10 drivers/block/nbd.c:2026
       nbd_init+0x2c5/0x2e0 drivers/block/nbd.c:2743
       do_one_initcall+0x11c/0x6f0 init/main.c:1362
       do_initcall_level init/main.c:1424 [inline]
       do_initcalls init/main.c:1440 [inline]
       do_basic_setup init/main.c:1460 [inline]
       kernel_init_freeable+0x6ea/0x7b0 init/main.c:1675
       kernel_init+0x21/0x1e0 init/main.c:1565
       ret_from_fork+0x730/0xd60 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #3 (&q->elevator_lock){+.+.}-{4:4}:
       lock_acquire kernel/locking/lockdep.c:5942 [inline]
       lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5899
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x1a4/0x1bd0 kernel/locking/mutex.c:821
       elevator_change+0x1bc/0x530 block/elevator.c:679
       elevator_set_none+0x92/0xf0 block/elevator.c:769
       blk_mq_elv_switch_none block/blk-mq.c:5102 [inline]
       __blk_mq_update_nr_hw_queues block/blk-mq.c:5147 [inline]
       blk_mq_update_nr_hw_queues+0x4c1/0x15f0 block/blk-mq.c:5212
       nbd_start_device+0x1a6/0xbd0 drivers/block/nbd.c:1530
       nbd_genl_connect+0xfc2/0x1760 drivers/block/nbd.c:2310
       genl_family_rcv_msg_doit+0x214/0x300 net/netlink/genetlink.c:1114
       genl_family_rcv_msg net/netlink/genetlink.c:1194 [inline]
       genl_rcv_msg+0x560/0x800 net/netlink/genetlink.c:1209
       netlink_rcv_skb+0x159/0x420 net/netlink/af_netlink.c:2575
       genl_rcv+0x28/0x40 net/netlink/genetlink.c:1218
       netlink_unicast_kernel net/netlink/af_netlink.c:1338 [inline]
       netlink_unicast+0x585/0x850 net/netlink/af_netlink.c:1364
       netlink_sendmsg+0x8b0/0xda0 net/netlink/af_netlink.c:1919
       sock_sendmsg_nosec net/socket.c:800 [inline]
       __sock_sendmsg net/socket.c:815 [inline]
       ____sys_sendmsg+0xa4d/0xbe0 net/socket.c:2713
       ___sys_sendmsg+0x190/0x1e0 net/socket.c:2767
       __sys_sendmsg+0x160/0x210 net/socket.c:2799
       do_syscall_32_irqs_on arch/x86/entry/syscall_32.c:79 [inline]
       __do_fast_syscall_32+0x13a/0x8b0 arch/x86/entry/syscall_32.c:291
       do_fast_syscall_32+0x32/0x70 arch/x86/entry/syscall_32.c:316
       entry_SYSENTER_compat_after_hwframe+0x84/0x8e

-> #2 (&q->q_usage_counter(io)#49){++++}-{0:0}:
       lock_acquire kernel/locking/lockdep.c:5942 [inline]
       lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5899
       blk_alloc_queue+0x610/0x790 block/blk-core.c:504
       blk_mq_alloc_queue+0x174/0x290 block/blk-mq.c:4420
       __blk_mq_alloc_disk+0x29/0x120 block/blk-mq.c:4467
       nbd_dev_add+0x491/0xb10 drivers/block/nbd.c:1996
       nbd_init+0x2c5/0x2e0 drivers/block/nbd.c:2743
       do_one_initcall+0x11c/0x6f0 init/main.c:1362
       do_initcall_level init/main.c:1424 [inline]
       do_initcalls init/main.c:1440 [inline]
       do_basic_setup init/main.c:1460 [inline]
       kernel_init_freeable+0x6ea/0x7b0 init/main.c:1675
       kernel_init+0x21/0x1e0 init/main.c:1565
       ret_from_fork+0x730/0xd60 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #1 (fs_reclaim){+.+.}-{0:0}:
       lock_acquire kernel/locking/lockdep.c:5942 [inline]
       lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5899
       __fs_reclaim_acquire mm/page_alloc.c:4375 [inline]
       fs_reclaim_acquire+0xc4/0x100 mm/page_alloc.c:4389
       might_alloc include/linux/sched/mm.h:316 [inline]
       slab_pre_alloc_hook mm/slub.c:4636 [inline]
       slab_alloc_node mm/slub.c:4974 [inline]
       kmem_cache_alloc_noprof+0x63/0x6a0 mm/slub.c:5010
       __kernfs_iattrs+0x126/0x450 fs/kernfs/inode.c:36
       kernfs_iattrs fs/kernfs/inode.c:60 [inline]
       __kernfs_setattr+0x4d/0x3c0 fs/kernfs/inode.c:73
       kernfs_iop_setattr+0xda/0x130 fs/kernfs/inode.c:127
       notify_change+0xb25/0x1330 fs/attr.c:556
       do_truncate+0x1df/0x240 fs/open.c:68
       handle_truncate fs/namei.c:4300 [inline]
       do_open fs/namei.c:4841 [inline]
       path_openat+0x1e6d/0x2440 fs/namei.c:5000
       do_file_open+0x20e/0x430 fs/namei.c:5029
       do_sys_openat2+0x10f/0x1e0 fs/open.c:1417
       do_sys_open fs/open.c:1423 [inline]
       __do_sys_openat fs/open.c:1439 [inline]
       __se_sys_openat fs/open.c:1434 [inline]
       __x64_sys_openat+0x12d/0x210 fs/open.c:1434
       do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
       do_syscall_64+0x121/0x770 arch/x86/entry/syscall_64.c:84
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (&root->kernfs_iattr_rwsem){++++}-{4:4}:
       check_prev_add+0xeb/0xe60 kernel/locking/lockdep.c:3209
       check_prevs_add kernel/locking/lockdep.c:3328 [inline]
       validate_chain kernel/locking/lockdep.c:3952 [inline]
       __lock_acquire+0x1528/0x1f40 kernel/locking/lockdep.c:5288
       lock_acquire kernel/locking/lockdep.c:5942 [inline]
       lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5899
       down_write+0x8b/0x1f0 kernel/locking/rwsem.c:1631
       kernfs_link_sibling+0x555/0x850 fs/kernfs/dir.c:411
       kernfs_add_one+0x1e7/0xaa0 fs/kernfs/dir.c:844
       kernfs_create_dir_ns+0x157/0x2b0 fs/kernfs/dir.c:1130
       sysfs_create_dir_ns+0x13a/0x2b0 fs/sysfs/dir.c:59
       create_dir lib/kobject.c:73 [inline]
       kobject_add_internal+0x2c8/0x930 lib/kobject.c:240
       kobject_add_varg lib/kobject.c:374 [inline]
       kobject_add+0x16a/0x1e0 lib/kobject.c:426
       device_add+0x294/0x1970 drivers/base/core.c:3699
       hci_conn_add_sysfs+0x1a3/0x260 net/bluetooth/hci_sysfs.c:61
       hci_conn_complete_evt+0x5bb/0x13f0 net/bluetooth/hci_event.c:3242
       hci_event_func net/bluetooth/hci_event.c:7887 [inline]
       hci_event_packet+0x8e9/0xcd0 net/bluetooth/hci_event.c:7938
       hci_rx_work+0x451/0xfc0 net/bluetooth/hci_core.c:4087
       process_one_work+0xac7/0x1b10 kernel/workqueue.c:3396
       process_scheduled_works kernel/workqueue.c:3479 [inline]
       worker_thread+0x5ef/0xe50 kernel/workqueue.c:3560
       kthread+0x373/0x450 kernel/kthread.c:436
       ret_from_fork+0x730/0xd60 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:

Chain exists of:
  &root->kernfs_iattr_rwsem --> cpuhp_state_mutex --> &root->kernfs_rwsem

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&root->kernfs_rwsem);
                               lock(cpuhp_state_mutex);
                               lock(&root->kernfs_rwsem);
  lock(&root->kernfs_iattr_rwsem);

 *** DEADLOCK ***

locks held by kworker/u34:0/27988: 4, last CPU#0:
 #0: ffff88802a3f9140 ((wq_completion)hci1#2){+.+.}-{0:0}, at: process_one_work+0x1466/0x1b10 kernel/workqueue.c:3371
 #1: ffffc9000d4bfd08 ((work_completion)(&hdev->rx_work)){+.+.}-{0:0}, at: process_one_work+0xa2c/0x1b10 kernel/workqueue.c:3372
 #2: ffff888069cd40b8 (&hdev->lock){+.+.}-{4:4}, at: hci_conn_complete_evt+0xbc/0x13f0 net/bluetooth/hci_event.c:3159
 #3: ffff88801d6c7180 (&root->kernfs_rwsem){++++}-{4:4}, at: kernfs_add_one+0x38/0xaa0 fs/kernfs/dir.c:825

stack backtrace:
CPU: 0 UID: 0 PID: 27988 Comm: kworker/u34:0 Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
Workqueue: hci1 hci_rx_work
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
 print_circular_bug.cold+0x178/0x1be kernel/locking/lockdep.c:2087
 check_noncircular+0x146/0x160 kernel/locking/lockdep.c:2219
 check_prev_add+0xeb/0xe60 kernel/locking/lockdep.c:3209
 check_prevs_add kernel/locking/lockdep.c:3328 [inline]
 validate_chain kernel/locking/lockdep.c:3952 [inline]
 __lock_acquire+0x1528/0x1f40 kernel/locking/lockdep.c:5288
 lock_acquire kernel/locking/lockdep.c:5942 [inline]
 lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5899
 down_write+0x8b/0x1f0 kernel/locking/rwsem.c:1631
 kernfs_link_sibling+0x555/0x850 fs/kernfs/dir.c:411
 kernfs_add_one+0x1e7/0xaa0 fs/kernfs/dir.c:844
 kernfs_create_dir_ns+0x157/0x2b0 fs/kernfs/dir.c:1130
 sysfs_create_dir_ns+0x13a/0x2b0 fs/sysfs/dir.c:59
 create_dir lib/kobject.c:73 [inline]
 kobject_add_internal+0x2c8/0x930 lib/kobject.c:240
 kobject_add_varg lib/kobject.c:374 [inline]
 kobject_add+0x16a/0x1e0 lib/kobject.c:426
 device_add+0x294/0x1970 drivers/base/core.c:3699
 hci_conn_add_sysfs+0x1a3/0x260 net/bluetooth/hci_sysfs.c:61
 hci_conn_complete_evt+0x5bb/0x13f0 net/bluetooth/hci_event.c:3242
 hci_event_func net/bluetooth/hci_event.c:7887 [inline]
 hci_event_packet+0x8e9/0xcd0 net/bluetooth/hci_event.c:7938
 hci_rx_work+0x451/0xfc0 net/bluetooth/hci_core.c:4087
 process_one_work+0xac7/0x1b10 kernel/workqueue.c:3396
 process_scheduled_works kernel/workqueue.c:3479 [inline]
 worker_thread+0x5ef/0xe50 kernel/workqueue.c:3560
 kthread+0x373/0x450 kernel/kthread.c:436
 ret_from_fork+0x730/0xd60 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>
bluetooth hci1:200: No ACPI support
PM: Adding info for No Bus:hci1:200
kobject: 'hci1:200' (ffff888024c1ccf0): kobject_uevent_env
kobject: 'hci1:200' (ffff888024c1ccf0): fill_kobj_path: path = '/devices/virtual/bluetooth/hci1/hci1:200'
hci1 opcode 0x041b plen 2
hci1: skb len 5
hci1 opcode 0x040f plen 4
hci1: skb len 7
hci1 Event packet
hci1: event 0x0b
hci1: status 0x00
hci1 opcode 0x0419 plen 10
hci1: skb len 13
hcon ffff888024c1c000 bdaddr 10:aa:aa:aa:aa:aa status 0
hci1 hcon ffff888024c1c000
hcon ffff888024c1c000 conn ffff888069e8b800 hchan ffff888013a2e800
conn ffff888069e8b800
conn ffff888069e8b800, code 0x0a, ident 0x01, len 2
code 0x0a
hci1 chan ffff888013a2e800 flags 0x0002
hci1 nonfrag skb ffff888078ebe000 len 14
hci1: chan ffff888013a2e800 queued 1
hcon ffff888024c1c000 orig refcnt 1
hci1 Event packet
hci1: event 0x3e
hci1: subevent 0x01
hci1: status 0x00
hci1: dst 11:aa:aa:aa:aa:aa
hci1: dst 11:aa:aa:aa:aa:aa handle 0x0f00
hci1 orig refcnt 10
hci1: conn ffff888026418000
hci1: hcon ffff888026418000 handle 0x00c9
channel 3 len 19
hci1: conn ffff888026418000
device: 'hci1:201': device_add
kobject: 'hci1:201' (ffff888026418cf0): kobject_add_internal: parent: 'hci1', set: 'devices'
bluetooth hci1:201: No ACPI support
PM: Adding info for No Bus:hci1:201
kobject: 'hci1:201' (ffff888026418cf0): kobject_uevent_env
kobject: 'hci1:201' (ffff888026418cf0): fill_kobj_path: path = '/devices/virtual/bluetooth/hci1/hci1:201'
hcon ffff888026418000 bdaddr 11:aa:aa:aa:aa:aa status 0
hci1 hcon ffff888026418000
hcon ffff888026418000 conn ffff888069e8b000 hchan ffff888029173c00
conn ffff888069e8b000
hci1 conn ffff888069e8b000
conn ffff888069e8b000, code 0x12, ident 0x01, len 8
code 0x12
hci1 chan ffff888029173c00 flags 0x0000
hci1 nonfrag skb ffff888078ebe500 len 20
hci1: chan ffff888029173c00 queued 1
hci1: 
hci1: entry ffff888060160d00
hci1: entry ffff888060160000
hci1
Bluetooth: hci1: command tx timeout
hci1 cmd_cnt 1 cmd queued 3
hci1: skb ffff88804bd33b80
hci1 type 1 len 5
hci1 acl 4 sco 0 le 0 iso 0
hci1: type 0
hci1: type 2
hci1
hci1
hci1
hci1
hci1
chan ffff888013a2e800 quote 4
chan ffff888013a2e800 skb ffff888078ebe000 len 14 priority 7
hcon ffff888024c1c000 mode 0
hci1 type 2 len 14
hci1: type 0
hci1: type 2
hci1
hci1
hci1
hci1
chan ffff888029173c00 quote 3
chan ffff888029173c00 skb ffff888078ebe500 len 20 priority 7
hci1 type 2 len 20
hci1: type 0
hci1: type 2
hci1
hci1