====================================================== WARNING: possible circular locking dependency detected syzkaller #0 Not tainted ------------------------------------------------------ syz.2.1452/11636 is trying to acquire lock: ffff88801c2d4a10 (&root->kernfs_iattr_rwsem){++++}-{4:4}, at: kernfs_link_sibling+0x4c7/0x5a0 fs/kernfs/dir.c:411 but task is already holding lock: ffff88801c2d4980 (&root->kernfs_rwsem){++++}-{4:4}, at: kernfs_add_one+0x41/0x6f0 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}: down_write+0x96/0x200 kernel/locking/rwsem.c:1631 kernfs_add_one+0x41/0x6f0 fs/kernfs/dir.c:825 kernfs_create_dir_ns+0x1a1/0x230 fs/kernfs/dir.c:1130 internal_create_group+0x440/0x1180 fs/sysfs/group.c:176 cpuhp_invoke_callback+0x434/0x810 kernel/cpu.c:194 cpuhp_issue_call+0x3f0/0x750 kernel/cpu.c:-1 __cpuhp_setup_state_cpuslocked+0x3f4/0x6f0 kernel/cpu.c:2507 __cpuhp_setup_state+0x3f/0x60 kernel/cpu.c:2536 do_one_initcall+0x250/0x870 init/main.c:1362 do_initcall_level+0x10a/0x1a0 init/main.c:1424 do_initcalls+0x59/0xa0 init/main.c:1440 kernel_init_freeable+0x29d/0x3e0 init/main.c:1675 kernel_init+0x22/0x1d0 init/main.c:1565 ret_from_fork+0x514/0xb70 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}: percpu_down_read_internal include/linux/percpu-rwsem.h:53 [inline] percpu_down_read include/linux/percpu-rwsem.h:77 [inline] cpus_read_lock+0x42/0x160 kernel/cpu.c:490 static_key_slow_inc+0x12/0x30 kernel/jump_label.c:190 nbd_genl_reconnect_sock_cb+0x69a/0xbb0 drivers/block/nbd.c:1377 nbd_genl_foreach_sock+0x265/0x450 drivers/block/nbd.c:2152 nbd_genl_reconfigure+0xbbb/0x1040 drivers/block/nbd.c:2477 genl_family_rcv_msg_doit+0x233/0x340 net/netlink/genetlink.c:1114 genl_family_rcv_msg net/netlink/genetlink.c:1194 [inline] genl_rcv_msg+0x614/0x7a0 net/netlink/genetlink.c:1209 netlink_rcv_skb+0x226/0x4a0 net/netlink/af_netlink.c:2572 genl_rcv+0x28/0x40 net/netlink/genetlink.c:1218 netlink_unicast_kernel net/netlink/af_netlink.c:1335 [inline] netlink_unicast+0x7bd/0x940 net/netlink/af_netlink.c:1361 netlink_sendmsg+0x813/0xb40 net/netlink/af_netlink.c:1916 sock_sendmsg_nosec+0x13a/0x180 net/socket.c:800 __sock_sendmsg net/socket.c:815 [inline] ____sys_sendmsg+0x54e/0x850 net/socket.c:2712 ___sys_sendmsg+0x2a5/0x360 net/socket.c:2766 __sys_sendmsg net/socket.c:2798 [inline] __do_sys_sendmsg net/socket.c:2803 [inline] __se_sys_sendmsg net/socket.c:2801 [inline] __x64_sys_sendmsg+0x1b1/0x290 net/socket.c:2801 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline] do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84 entry_SYSCALL_64_after_hwframe+0x77/0x7f -> #6 (&nsock->tx_lock){+.+.}-{4:4}: __mutex_lock_common kernel/locking/mutex.c:646 [inline] __mutex_lock+0x19d/0x1550 kernel/locking/mutex.c:821 nbd_handle_cmd drivers/block/nbd.c:1143 [inline] nbd_queue_rq+0x373/0xff0 drivers/block/nbd.c:1207 blk_mq_dispatch_rq_list+0x499/0x1990 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+0xd36/0x1580 block/blk-mq-sched.c:307 blk_mq_sched_dispatch_requests+0xd7/0x190 block/blk-mq-sched.c:329 blk_mq_run_work_fn+0x16c/0x300 block/blk-mq.c:2532 process_one_work kernel/workqueue.c:3396 [inline] process_scheduled_works+0xc3d/0x1630 kernel/workqueue.c:3479 worker_thread+0xa47/0xfb0 kernel/workqueue.c:3560 kthread+0x38b/0x480 kernel/kthread.c:436 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 -> #5 (&cmd->lock){+.+.}-{4:4}: __mutex_lock_common kernel/locking/mutex.c:646 [inline] __mutex_lock+0x19d/0x1550 kernel/locking/mutex.c:821 nbd_queue_rq+0xc1/0xff0 drivers/block/nbd.c:1199 blk_mq_dispatch_rq_list+0x499/0x1990 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+0xd36/0x1580 block/blk-mq-sched.c:307 blk_mq_sched_dispatch_requests+0xd7/0x190 block/blk-mq-sched.c:329 blk_mq_run_work_fn+0x16c/0x300 block/blk-mq.c:2532 process_one_work kernel/workqueue.c:3396 [inline] process_scheduled_works+0xc3d/0x1630 kernel/workqueue.c:3479 worker_thread+0xa47/0xfb0 kernel/workqueue.c:3560 kthread+0x38b/0x480 kernel/kthread.c:436 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 -> #4 (set->srcu){.+.+}-{0:0}: srcu_lock_sync include/linux/srcu.h:210 [inline] __synchronize_srcu+0xc9/0x2f0 kernel/rcu/srcutree.c:1462 elevator_switch+0x1e8/0x7b0 block/elevator.c:576 elevator_change+0x2fa/0x480 block/elevator.c:681 elevator_set_default+0x375/0x440 block/elevator.c:754 blk_register_queue+0x3f3/0x4e0 block/blk-sysfs.c:992 __add_disk+0x6b8/0xdb0 block/genhd.c:531 add_disk_fwnode+0x100/0x3a0 block/genhd.c:600 add_disk include/linux/blkdev.h:798 [inline] nbd_dev_add+0x733/0xb60 drivers/block/nbd.c:2026 nbd_init+0x168/0x1f0 drivers/block/nbd.c:2743 do_one_initcall+0x250/0x870 init/main.c:1362 do_initcall_level+0x10a/0x1a0 init/main.c:1424 do_initcalls+0x59/0xa0 init/main.c:1440 kernel_init_freeable+0x29d/0x3e0 init/main.c:1675 kernel_init+0x22/0x1d0 init/main.c:1565 ret_from_fork+0x514/0xb70 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}: __mutex_lock_common kernel/locking/mutex.c:646 [inline] __mutex_lock+0x19d/0x1550 kernel/locking/mutex.c:821 elevator_change+0x1af/0x480 block/elevator.c:679 elevator_set_none+0xb5/0x140 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+0x5ef/0x19f0 block/blk-mq.c:5212 nbd_start_device+0x189/0xb30 drivers/block/nbd.c:1530 nbd_genl_connect+0x167d/0x1cd0 drivers/block/nbd.c:2310 genl_family_rcv_msg_doit+0x233/0x340 net/netlink/genetlink.c:1114 genl_family_rcv_msg net/netlink/genetlink.c:1194 [inline] genl_rcv_msg+0x614/0x7a0 net/netlink/genetlink.c:1209 netlink_rcv_skb+0x226/0x4a0 net/netlink/af_netlink.c:2572 genl_rcv+0x28/0x40 net/netlink/genetlink.c:1218 netlink_unicast_kernel net/netlink/af_netlink.c:1335 [inline] netlink_unicast+0x7bd/0x940 net/netlink/af_netlink.c:1361 netlink_sendmsg+0x813/0xb40 net/netlink/af_netlink.c:1916 sock_sendmsg_nosec+0x13a/0x180 net/socket.c:800 __sock_sendmsg net/socket.c:815 [inline] ____sys_sendmsg+0x54e/0x850 net/socket.c:2712 ___sys_sendmsg+0x2a5/0x360 net/socket.c:2766 __sys_sendmsg net/socket.c:2798 [inline] __do_sys_sendmsg net/socket.c:2803 [inline] __se_sys_sendmsg net/socket.c:2801 [inline] __x64_sys_sendmsg+0x1b1/0x290 net/socket.c:2801 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline] do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84 entry_SYSCALL_64_after_hwframe+0x77/0x7f -> #2 (&q->q_usage_counter(io)#53){++++}-{0:0}: blk_alloc_queue+0x544/0x690 block/blk-core.c:504 blk_mq_alloc_queue block/blk-mq.c:4420 [inline] __blk_mq_alloc_disk+0x194/0x390 block/blk-mq.c:4467 nbd_dev_add+0x494/0xb60 drivers/block/nbd.c:1996 nbd_init+0x168/0x1f0 drivers/block/nbd.c:2743 do_one_initcall+0x250/0x870 init/main.c:1362 do_initcall_level+0x10a/0x1a0 init/main.c:1424 do_initcalls+0x59/0xa0 init/main.c:1440 kernel_init_freeable+0x29d/0x3e0 init/main.c:1675 kernel_init+0x22/0x1d0 init/main.c:1565 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 -> #1 (fs_reclaim){+.+.}-{0:0}: __fs_reclaim_acquire mm/page_alloc.c:4375 [inline] fs_reclaim_acquire+0x71/0x100 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+0x5f/0x600 mm/slub.c:5010 __kernfs_iattrs+0xdd/0x380 fs/kernfs/inode.c:36 kernfs_iattrs fs/kernfs/inode.c:60 [inline] __kernfs_setattr fs/kernfs/inode.c:73 [inline] kernfs_iop_setattr+0xe6/0x3f0 fs/kernfs/inode.c:127 notify_change+0xbba/0xea0 fs/attr.c:556 do_truncate+0x1c2/0x250 fs/open.c:68 handle_truncate fs/namei.c:4300 [inline] do_open fs/namei.c:4841 [inline] path_openat+0x15b5/0x1d60 fs/namei.c:5000 do_file_open+0x23e/0x4a0 fs/namei.c:5029 do_sys_openat2+0x115/0x200 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+0x138/0x170 fs/open.c:1434 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline] do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84 entry_SYSCALL_64_after_hwframe+0x77/0x7f -> #0 (&root->kernfs_iattr_rwsem){++++}-{4:4}: check_prev_add kernel/locking/lockdep.c:3209 [inline] check_prevs_add kernel/locking/lockdep.c:3328 [inline] validate_chain kernel/locking/lockdep.c:3952 [inline] __lock_acquire+0x164c/0x2de0 kernel/locking/lockdep.c:5288 lock_acquire+0x115/0x350 kernel/locking/lockdep.c:5942 down_write+0x96/0x200 kernel/locking/rwsem.c:1631 kernfs_link_sibling+0x4c7/0x5a0 fs/kernfs/dir.c:411 kernfs_add_one+0x2db/0x6f0 fs/kernfs/dir.c:844 __kernfs_create_file+0x22b/0x2e0 fs/kernfs/file.c:1079 sysfs_add_file_mode_ns+0x237/0x300 fs/sysfs/file.c:316 sysfs_create_file_ns+0x12b/0x1b0 fs/sysfs/file.c:377 sysfs_create_file include/linux/sysfs.h:774 [inline] idletimer_tg_create net/netfilter/xt_IDLETIMER.c:169 [inline] idletimer_tg_checkentry+0x3f7/0x810 net/netfilter/xt_IDLETIMER.c:328 xt_checkentry_target net/netfilter/x_tables.c:1115 [inline] xt_check_target+0x619/0xca0 net/netfilter/x_tables.c:1138 check_target net/ipv6/netfilter/ip6_tables.c:528 [inline] find_check_entry net/ipv6/netfilter/ip6_tables.c:571 [inline] translate_table+0x1917/0x2110 net/ipv6/netfilter/ip6_tables.c:738 do_replace net/ipv6/netfilter/ip6_tables.c:1157 [inline] do_ip6t_set_ctl+0xa5c/0xe30 net/ipv6/netfilter/ip6_tables.c:1648 nf_setsockopt+0x26f/0x290 net/netfilter/nf_sockopt.c:101 do_sock_setsockopt+0x17c/0x1b0 net/socket.c:2396 __sys_setsockopt net/socket.c:2421 [inline] __do_sys_setsockopt net/socket.c:2427 [inline] __se_sys_setsockopt net/socket.c:2424 [inline] __x64_sys_setsockopt+0x13d/0x1b0 net/socket.c:2424 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline] do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84 entry_SYSCALL_64_after_hwframe+0x77/0x7f 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 syz.2.1452/11636: 2, last CPU#1: #0: ffffffff903027e0 (list_mutex){+.+.}-{4:4}, at: idletimer_tg_checkentry+0x63/0x810 net/netfilter/xt_IDLETIMER.c:314 #1: ffff88801c2d4980 (&root->kernfs_rwsem){++++}-{4:4}, at: kernfs_add_one+0x41/0x6f0 fs/kernfs/dir.c:825 stack backtrace: CPU: 1 UID: 0 PID: 11636 Comm: syz.2.1452 Not tainted syzkaller #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026 Call Trace: dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120 print_circular_bug+0x2e2/0x300 kernel/locking/lockdep.c:2087 check_noncircular+0x12f/0x150 kernel/locking/lockdep.c:2219 check_prev_add kernel/locking/lockdep.c:3209 [inline] check_prevs_add kernel/locking/lockdep.c:3328 [inline] validate_chain kernel/locking/lockdep.c:3952 [inline] __lock_acquire+0x164c/0x2de0 kernel/locking/lockdep.c:5288 lock_acquire+0x115/0x350 kernel/locking/lockdep.c:5942 down_write+0x96/0x200 kernel/locking/rwsem.c:1631 kernfs_link_sibling+0x4c7/0x5a0 fs/kernfs/dir.c:411 kernfs_add_one+0x2db/0x6f0 fs/kernfs/dir.c:844 __kernfs_create_file+0x22b/0x2e0 fs/kernfs/file.c:1079 sysfs_add_file_mode_ns+0x237/0x300 fs/sysfs/file.c:316 sysfs_create_file_ns+0x12b/0x1b0 fs/sysfs/file.c:377 sysfs_create_file include/linux/sysfs.h:774 [inline] idletimer_tg_create net/netfilter/xt_IDLETIMER.c:169 [inline] idletimer_tg_checkentry+0x3f7/0x810 net/netfilter/xt_IDLETIMER.c:328 xt_checkentry_target net/netfilter/x_tables.c:1115 [inline] xt_check_target+0x619/0xca0 net/netfilter/x_tables.c:1138 check_target net/ipv6/netfilter/ip6_tables.c:528 [inline] find_check_entry net/ipv6/netfilter/ip6_tables.c:571 [inline] translate_table+0x1917/0x2110 net/ipv6/netfilter/ip6_tables.c:738 do_replace net/ipv6/netfilter/ip6_tables.c:1157 [inline] do_ip6t_set_ctl+0xa5c/0xe30 net/ipv6/netfilter/ip6_tables.c:1648 nf_setsockopt+0x26f/0x290 net/netfilter/nf_sockopt.c:101 do_sock_setsockopt+0x17c/0x1b0 net/socket.c:2396 __sys_setsockopt net/socket.c:2421 [inline] __do_sys_setsockopt net/socket.c:2427 [inline] __se_sys_setsockopt net/socket.c:2424 [inline] __x64_sys_setsockopt+0x13d/0x1b0 net/socket.c:2424 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline] do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7faf50b9e159 Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007faf51a2c028 EFLAGS: 00000246 ORIG_RAX: 0000000000000036 RAX: ffffffffffffffda RBX: 00007faf50e25fa0 RCX: 00007faf50b9e159 RDX: 0000000000000040 RSI: 0000000000000029 RDI: 0000000000000006 RBP: 00007faf50c3506b R08: 00000000000005d8 R09: 0000000000000000 R10: 00002000000006c0 R11: 0000000000000246 R12: 0000000000000000 R13: 00007faf50e26038 R14: 00007faf50e25fa0 R15: 00007ffea39d87c8