====================================================== WARNING: possible circular locking dependency detected 6.17.0-rc1-syzkaller-00016-g8742b2d8935f #0 Not tainted ------------------------------------------------------ syz.5.200/6858 is trying to acquire lock: ffff88801b2f7988 (&root->kernfs_rwsem){++++}-{4:4}, at: kernfs_remove+0x30/0x60 fs/kernfs/dir.c:1549 but task is already holding lock: ffff888024b327e8 (&q->q_usage_counter(io)#54){++++}-{0:0}, at: nbd_start_device+0x17f/0xb10 drivers/block/nbd.c:1478 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #2 (&q->q_usage_counter(io)#54){++++}-{0:0}: lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868 blk_alloc_queue+0x538/0x620 block/blk-core.c:461 blk_mq_alloc_queue block/blk-mq.c:4400 [inline] __blk_mq_alloc_disk+0x15c/0x340 block/blk-mq.c:4447 nbd_dev_add+0x46c/0xae0 drivers/block/nbd.c:1943 nbd_init+0x168/0x1f0 drivers/block/nbd.c:2680 do_one_initcall+0x236/0x820 init/main.c:1269 do_initcall_level+0x104/0x190 init/main.c:1331 do_initcalls+0x59/0xa0 init/main.c:1347 kernel_init_freeable+0x334/0x4b0 init/main.c:1579 kernel_init+0x1d/0x1d0 init/main.c:1469 ret_from_fork+0x3fc/0x770 arch/x86/kernel/process.c:148 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 -> #1 (fs_reclaim){+.+.}-{0:0}: lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868 __fs_reclaim_acquire mm/page_alloc.c:4234 [inline] fs_reclaim_acquire+0x72/0x100 mm/page_alloc.c:4248 might_alloc include/linux/sched/mm.h:318 [inline] slab_pre_alloc_hook mm/slub.c:4131 [inline] slab_alloc_node mm/slub.c:4209 [inline] kmem_cache_alloc_lru_noprof+0x49/0x3d0 mm/slub.c:4248 alloc_inode+0xb8/0x1b0 fs/inode.c:348 iget_locked+0xf0/0x570 fs/inode.c:1438 kernfs_get_inode+0x4f/0x780 fs/kernfs/inode.c:253 kernfs_fill_super fs/kernfs/mount.c:307 [inline] kernfs_get_tree+0x5a9/0x920 fs/kernfs/mount.c:391 sysfs_get_tree+0x46/0x110 fs/sysfs/mount.c:31 vfs_get_tree+0x92/0x2b0 fs/super.c:1815 do_new_mount+0x2a2/0x9e0 fs/namespace.c:3805 do_mount fs/namespace.c:4133 [inline] __do_sys_mount fs/namespace.c:4344 [inline] __se_sys_mount+0x317/0x410 fs/namespace.c:4321 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f -> #0 (&root->kernfs_rwsem){++++}-{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 down_write+0x96/0x1f0 kernel/locking/rwsem.c:1590 kernfs_remove+0x30/0x60 fs/kernfs/dir.c:1549 __kobject_del+0xe1/0x300 lib/kobject.c:604 kobject_del+0x45/0x60 lib/kobject.c:627 elv_unregister_queue block/elevator.c:503 [inline] elevator_change_done+0xef/0x540 block/elevator.c:646 elevator_change+0x332/0x450 block/elevator.c:694 elevator_set_none+0x42/0xb0 block/elevator.c:781 blk_mq_elv_switch_none block/blk-mq.c:5023 [inline] __blk_mq_update_nr_hw_queues block/blk-mq.c:5068 [inline] blk_mq_update_nr_hw_queues+0x72c/0x19a0 block/blk-mq.c:5119 nbd_start_device+0x17f/0xb10 drivers/block/nbd.c:1478 nbd_start_device_ioctl drivers/block/nbd.c:1537 [inline] __nbd_ioctl drivers/block/nbd.c:1612 [inline] nbd_ioctl+0x636/0xeb0 drivers/block/nbd.c:1652 blkdev_ioctl+0x5a8/0x6d0 block/ioctl.c:705 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:598 [inline] __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:584 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f other info that might help us debug this: Chain exists of: &root->kernfs_rwsem --> fs_reclaim --> &q->q_usage_counter(io)#54 Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&q->q_usage_counter(io)#54); lock(fs_reclaim); lock(&q->q_usage_counter(io)#54); lock(&root->kernfs_rwsem); *** DEADLOCK *** 4 locks held by syz.5.200/6858: #0: ffff888025045188 (&set->update_nr_hwq_lock){++++}-{4:4}, at: blk_mq_update_nr_hw_queues+0xa7/0x19a0 block/blk-mq.c:5117 #1: ffff8880250450d8 (&set->tag_list_lock){+.+.}-{4:4}, at: blk_mq_update_nr_hw_queues+0xba/0x19a0 block/blk-mq.c:5118 #2: ffff888024b327e8 (&q->q_usage_counter(io)#54){++++}-{0:0}, at: nbd_start_device+0x17f/0xb10 drivers/block/nbd.c:1478 #3: ffff888024b32820 (&q->q_usage_counter(queue)#6){+.+.}-{0:0}, at: nbd_start_device+0x17f/0xb10 drivers/block/nbd.c:1478 stack backtrace: CPU: 0 UID: 0 PID: 6858 Comm: syz.5.200 Not tainted 6.17.0-rc1-syzkaller-00016-g8742b2d8935f #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025 Call Trace: 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 down_write+0x96/0x1f0 kernel/locking/rwsem.c:1590 kernfs_remove+0x30/0x60 fs/kernfs/dir.c:1549 __kobject_del+0xe1/0x300 lib/kobject.c:604 kobject_del+0x45/0x60 lib/kobject.c:627 elv_unregister_queue block/elevator.c:503 [inline] elevator_change_done+0xef/0x540 block/elevator.c:646 elevator_change+0x332/0x450 block/elevator.c:694 elevator_set_none+0x42/0xb0 block/elevator.c:781 blk_mq_elv_switch_none block/blk-mq.c:5023 [inline] __blk_mq_update_nr_hw_queues block/blk-mq.c:5068 [inline] blk_mq_update_nr_hw_queues+0x72c/0x19a0 block/blk-mq.c:5119 nbd_start_device+0x17f/0xb10 drivers/block/nbd.c:1478 nbd_start_device_ioctl drivers/block/nbd.c:1537 [inline] __nbd_ioctl drivers/block/nbd.c:1612 [inline] nbd_ioctl+0x636/0xeb0 drivers/block/nbd.c:1652 blkdev_ioctl+0x5a8/0x6d0 block/ioctl.c:705 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:598 [inline] __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:584 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7fbdd198ebe9 Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 a8 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007fbdd2783038 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 RAX: ffffffffffffffda RBX: 00007fbdd1bb6090 RCX: 00007fbdd198ebe9 RDX: 0000000000000000 RSI: 000000000000ab03 RDI: 0000000000000003 RBP: 00007fbdd1a11e19 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 R13: 00007fbdd1bb6128 R14: 00007fbdd1bb6090 R15: 00007ffe3eae35e8