======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Tainted: G             L     
------------------------------------------------------
kworker/u9:0/52 is trying to acquire lock:
ffff88801e2c4980 (&root->kernfs_rwsem){++++}-{4:4}, at: kernfs_remove_by_name_ns+0x51/0x120 fs/kernfs/dir.c:1792

but task is already holding lock:
ffff88801e2c4aa0 (&root->kernfs_supers_rwsem){++++}-{4:4}, at: kernfs_remove_by_name_ns+0x49/0x120 fs/kernfs/dir.c:1791

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #8 (&root->kernfs_supers_rwsem){++++}-{4:4}:
       lock_acquire kernel/locking/lockdep.c:5942 [inline]
       lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5899
       down_read+0x99/0x4c0 kernel/locking/rwsem.c:1574
       kernfs_remove_by_name_ns+0x49/0x120 fs/kernfs/dir.c:1791
       kernfs_remove_by_name include/linux/kernfs.h:644 [inline]
       remove_files+0x96/0x1c0 fs/sysfs/group.c:28
       sysfs_remove_group+0x8b/0x1b0 fs/sysfs/group.c:328
       topology_remove_dev+0x22/0x30 drivers/base/topology.c:199
       cpuhp_invoke_callback+0x3b4/0x9a0 kernel/cpu.c:194
       __cpuhp_invoke_callback_range+0x158/0x1d0 kernel/cpu.c:972
       cpuhp_invoke_callback_range kernel/cpu.c:996 [inline]
       cpuhp_down_callbacks kernel/cpu.c:1386 [inline]
       _cpu_down+0x523/0x1020 kernel/cpu.c:1457
       cpu_down_maps_locked kernel/cpu.c:1483 [inline]
       cpuhp_smt_disable+0x11f/0x1f0 kernel/cpu.c:2670
       __store_smt_control kernel/cpu.c:2938 [inline]
       control_store+0x1a2/0x320 kernel/cpu.c:2983
       dev_attr_store+0x58/0x80 drivers/base/core.c:2509
       sysfs_kf_write+0xf2/0x150 fs/sysfs/file.c:145
       kernfs_fop_write_iter+0x3e0/0x5f0 fs/kernfs/file.c:345
       new_sync_write fs/read_write.c:595 [inline]
       vfs_write+0x6af/0x1050 fs/read_write.c:687
       ksys_write+0x12a/0x250 fs/read_write.c:739
       do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
       do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #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:2579
       genl_rcv+0x28/0x40 net/netlink/genetlink.c:1218
       netlink_unicast_kernel net/netlink/af_netlink.c:1338 [inline]
       netlink_unicast+0x65f/0x950 net/netlink/af_netlink.c:1364
       netlink_sendmsg+0x8b0/0xda0 net/netlink/af_netlink.c:1923
       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_x64 arch/x86/entry/syscall_64.c:61 [inline]
       do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #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:2130
       __blk_mq_sched_dispatch_requests+0x218/0x1620 block/blk-mq-sched.c:299
       blk_mq_sched_dispatch_requests+0xd7/0x1c0 block/blk-mq-sched.c:329
       blk_mq_run_hw_queue+0x23f/0x670 block/blk-mq.c:2368
       blk_mq_run_hw_queues+0x21d/0x6d0 block/blk-mq.c:2417
       blk_mq_requeue_work+0x59f/0x7d0 block/blk-mq.c:1584
       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:2130
       __blk_mq_sched_dispatch_requests+0x218/0x1620 block/blk-mq-sched.c:299
       blk_mq_sched_dispatch_requests+0xd7/0x1c0 block/blk-mq-sched.c:329
       blk_mq_run_hw_queue+0x23f/0x670 block/blk-mq.c:2368
       blk_mq_run_hw_queues+0x21d/0x6d0 block/blk-mq.c:2417
       blk_mq_requeue_work+0x59f/0x7d0 block/blk-mq.c:1584
       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
       elv_iosched_store+0x3be/0x460 block/elevator.c:826
       queue_attr_store+0x25f/0x2f0 block/blk-sysfs.c:906
       sysfs_kf_write+0xf2/0x150 fs/sysfs/file.c:145
       kernfs_fop_write_iter+0x3e0/0x5f0 fs/kernfs/file.c:345
       new_sync_write fs/read_write.c:595 [inline]
       vfs_write+0x6af/0x1050 fs/read_write.c:687
       ksys_write+0x12a/0x250 fs/read_write.c:739
       do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
       do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #2 (&q->q_usage_counter(io)#17){++++}-{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:4431
       __blk_mq_alloc_disk+0x29/0x120 block/blk-mq.c:4478
       loop_add+0x498/0xb60 drivers/block/loop.c:2073
       loop_init+0x1d3/0x200 drivers/block/loop.c:2312
       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_lru_noprof+0x5f/0x6a0 mm/slub.c:5029
       alloc_inode+0x183/0x250 fs/inode.c:340
       iget_locked+0x1d9/0x6d0 fs/inode.c:1472
       kernfs_get_inode+0x46/0x470 fs/kernfs/inode.c:250
       kernfs_fill_super fs/kernfs/mount.c:308 [inline]
       kernfs_get_tree+0x636/0xbb0 fs/kernfs/mount.c:392
       vfs_get_tree+0x92/0x320 fs/super.c:1932
       fc_mount fs/namespace.c:1278 [inline]
       do_new_mount_fc fs/namespace.c:3885 [inline]
       do_new_mount fs/namespace.c:3961 [inline]
       path_mount+0x7d0/0x2850 fs/namespace.c:4312
       do_mount fs/namespace.c:4325 [inline]
       __do_sys_mount fs/namespace.c:4543 [inline]
       __se_sys_mount fs/namespace.c:4520 [inline]
       __x64_sys_mount+0x293/0x310 fs/namespace.c:4520
       do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
       do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (&root->kernfs_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_remove_by_name_ns+0x51/0x120 fs/kernfs/dir.c:1792
       kernfs_remove_by_name include/linux/kernfs.h:644 [inline]
       sysfs_unmerge_group+0xe7/0x170 fs/sysfs/group.c:408
       dpm_sysfs_remove+0x68/0xb0 drivers/base/power/sysfs.c:830
       device_del+0x180/0x9b0 drivers/base/core.c:3940
       device_unregister+0x1d/0xe0 drivers/base/core.c:4006
       hci_conn_del_sysfs+0xb9/0x1a0 net/bluetooth/hci_sysfs.c:92
       hci_conn_cleanup net/bluetooth/hci_conn.c:170 [inline]
       hci_conn_del+0x506/0x1180 net/bluetooth/hci_conn.c:1339
       hci_abort_conn_sync+0x7d9/0xb20 net/bluetooth/hci_sync.c:6035
       abort_conn_sync+0x142/0x350 net/bluetooth/hci_conn.c:3215
       hci_cmd_sync_work+0x1b6/0x4c0 net/bluetooth/hci_sync.c:338
       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_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/u9:0/52: 5, last CPU#0:
 #0: ffff88802c533940 ((wq_completion)hci4){+.+.}-{0:0}, at: process_one_work+0x1466/0x1b10 kernel/workqueue.c:3371
 #1: ffffc90000bc7d08 ((work_completion)(&hdev->cmd_sync_work)){+.+.}-{0:0}, at: process_one_work+0xa2c/0x1b10 kernel/workqueue.c:3372
 #2: ffff888064ac0ea0 (&hdev->req_lock){+.+.}-{4:4}, at: hci_cmd_sync_work+0x180/0x4c0 net/bluetooth/hci_sync.c:337
 #3: ffff888064ac00b8 (&hdev->lock){+.+.}-{4:4}, at: hci_abort_conn_sync+0x141/0xb20 net/bluetooth/hci_sync.c:6016
 #4: ffff88801e2c4aa0 (&root->kernfs_supers_rwsem){++++}-{4:4}, at: kernfs_remove_by_name_ns+0x49/0x120 fs/kernfs/dir.c:1791

stack backtrace:
CPU: 0 UID: 0 PID: 52 Comm: kworker/u9:0 Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/26/2026
Workqueue: hci4 hci_cmd_sync_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_remove_by_name_ns+0x51/0x120 fs/kernfs/dir.c:1792
 kernfs_remove_by_name include/linux/kernfs.h:644 [inline]
 sysfs_unmerge_group+0xe7/0x170 fs/sysfs/group.c:408
 dpm_sysfs_remove+0x68/0xb0 drivers/base/power/sysfs.c:830
 device_del+0x180/0x9b0 drivers/base/core.c:3940
 device_unregister+0x1d/0xe0 drivers/base/core.c:4006
 hci_conn_del_sysfs+0xb9/0x1a0 net/bluetooth/hci_sysfs.c:92
 hci_conn_cleanup net/bluetooth/hci_conn.c:170 [inline]
 hci_conn_del+0x506/0x1180 net/bluetooth/hci_conn.c:1339
 hci_abort_conn_sync+0x7d9/0xb20 net/bluetooth/hci_sync.c:6035
 abort_conn_sync+0x142/0x350 net/bluetooth/hci_conn.c:3215
 hci_cmd_sync_work+0x1b6/0x4c0 net/bluetooth/hci_sync.c:338
 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>