====================================================== WARNING: possible circular locking dependency detected 6.17.0-rc1-syzkaller-g8f5ae30d69d7 #0 Not tainted ------------------------------------------------------ syz.4.5/6683 is trying to acquire lock: ffff0000c18a3988 (&root->kernfs_rwsem){++++}-{4:4}, at: kernfs_remove+0x34/0x5c fs/kernfs/dir.c:1549 but task is already holding lock: ffff0000ca754520 (&q->q_usage_counter(io)#37){++++}-{0:0}, at: nbd_start_device+0x158/0xa48 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)#37){++++}-{0:0}: blk_alloc_queue+0x48c/0x54c block/blk-core.c:461 blk_mq_alloc_queue block/blk-mq.c:4400 [inline] __blk_mq_alloc_disk+0x124/0x304 block/blk-mq.c:4447 nbd_dev_add+0x398/0x820 drivers/block/nbd.c:1943 nbd_init+0x15c/0x174 drivers/block/nbd.c:2680 do_one_initcall+0x250/0x990 init/main.c:1269 do_initcall_level+0x128/0x1c4 init/main.c:1331 do_initcalls+0x70/0xd0 init/main.c:1347 do_basic_setup+0x78/0x8c init/main.c:1366 kernel_init_freeable+0x268/0x39c init/main.c:1579 kernel_init+0x24/0x1dc init/main.c:1469 ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:844 -> #1 (fs_reclaim){+.+.}-{0:0}: __fs_reclaim_acquire mm/page_alloc.c:4234 [inline] fs_reclaim_acquire+0x8c/0x118 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+0x5c/0x3ec mm/slub.c:4248 alloc_inode+0xb4/0x19c fs/inode.c:348 iget_locked+0x168/0x7b0 fs/inode.c:1438 kernfs_get_inode+0x58/0x66c fs/kernfs/inode.c:253 kernfs_fill_super fs/kernfs/mount.c:307 [inline] kernfs_get_tree+0x494/0x73c fs/kernfs/mount.c:391 sysfs_get_tree+0x48/0x120 fs/sysfs/mount.c:31 vfs_get_tree+0x90/0x28c fs/super.c:1815 do_new_mount+0x278/0x7f4 fs/namespace.c:3805 path_mount+0x5b4/0xde0 fs/namespace.c:4120 do_mount fs/namespace.c:4133 [inline] __do_sys_mount fs/namespace.c:4344 [inline] __se_sys_mount fs/namespace.c:4321 [inline] __arm64_sys_mount+0x3e8/0x468 fs/namespace.c:4321 __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline] invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:49 el0_svc_common+0x130/0x23c arch/arm64/kernel/syscall.c:132 do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:151 el0_svc+0x58/0x180 arch/arm64/kernel/entry-common.c:879 el0t_64_sync_handler+0x84/0x12c arch/arm64/kernel/entry-common.c:898 el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:596 -> #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 kernel/locking/lockdep.c:3908 [inline] __lock_acquire+0x1774/0x30a4 kernel/locking/lockdep.c:5237 lock_acquire+0x14c/0x2e0 kernel/locking/lockdep.c:5868 down_write+0x50/0xc0 kernel/locking/rwsem.c:1590 kernfs_remove+0x34/0x5c fs/kernfs/dir.c:1549 sysfs_remove_dir+0xa8/0xec fs/sysfs/dir.c:101 __kobject_del+0xe8/0x2d4 lib/kobject.c:604 kobject_del+0x48/0x68 lib/kobject.c:627 elv_unregister_queue block/elevator.c:503 [inline] elevator_change_done+0xd8/0x554 block/elevator.c:646 elevator_change+0x2b8/0x3cc block/elevator.c:694 elevator_set_none+0x48/0xac 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+0x610/0x149c block/blk-mq.c:5119 nbd_start_device+0x158/0xa48 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+0x52c/0xc4c drivers/block/nbd.c:1652 blkdev_ioctl+0x610/0xac0 block/ioctl.c:705 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:598 [inline] __se_sys_ioctl fs/ioctl.c:584 [inline] __arm64_sys_ioctl+0x14c/0x1c4 fs/ioctl.c:584 __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline] invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:49 el0_svc_common+0x130/0x23c arch/arm64/kernel/syscall.c:132 do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:151 el0_svc+0x58/0x180 arch/arm64/kernel/entry-common.c:879 el0t_64_sync_handler+0x84/0x12c arch/arm64/kernel/entry-common.c:898 el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:596 other info that might help us debug this: Chain exists of: &root->kernfs_rwsem --> fs_reclaim --> &q->q_usage_counter(io)#37 Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&q->q_usage_counter(io)#37); lock(fs_reclaim); lock(&q->q_usage_counter(io)#37); lock(&root->kernfs_rwsem); *** DEADLOCK *** 4 locks held by syz.4.5/6683: #0: ffff0000cad13988 (&set->update_nr_hwq_lock){++++}-{4:4}, at: blk_mq_update_nr_hw_queues+0x98/0x149c block/blk-mq.c:5117 #1: ffff0000cad138d8 (&set->tag_list_lock){+.+.}-{4:4}, at: blk_mq_update_nr_hw_queues+0xa4/0x149c block/blk-mq.c:5118 #2: ffff0000ca754520 (&q->q_usage_counter(io)#37){++++}-{0:0}, at: nbd_start_device+0x158/0xa48 drivers/block/nbd.c:1478 #3: ffff0000ca754558 (&q->q_usage_counter(queue)#5){+.+.}-{0:0}, at: nbd_start_device+0x158/0xa48 drivers/block/nbd.c:1478 stack backtrace: CPU: 1 UID: 0 PID: 6683 Comm: syz.4.5 Not tainted 6.17.0-rc1-syzkaller-g8f5ae30d69d7 #0 PREEMPT Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/18/2025 Call trace: show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:499 (C) __dump_stack+0x30/0x40 lib/dump_stack.c:94 dump_stack_lvl+0xd8/0x12c lib/dump_stack.c:120 dump_stack+0x1c/0x28 lib/dump_stack.c:129 print_circular_bug+0x324/0x32c kernel/locking/lockdep.c:2043 check_noncircular+0x154/0x174 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 kernel/locking/lockdep.c:3908 [inline] __lock_acquire+0x1774/0x30a4 kernel/locking/lockdep.c:5237 lock_acquire+0x14c/0x2e0 kernel/locking/lockdep.c:5868 down_write+0x50/0xc0 kernel/locking/rwsem.c:1590 kernfs_remove+0x34/0x5c fs/kernfs/dir.c:1549 sysfs_remove_dir+0xa8/0xec fs/sysfs/dir.c:101 __kobject_del+0xe8/0x2d4 lib/kobject.c:604 kobject_del+0x48/0x68 lib/kobject.c:627 elv_unregister_queue block/elevator.c:503 [inline] elevator_change_done+0xd8/0x554 block/elevator.c:646 elevator_change+0x2b8/0x3cc block/elevator.c:694 elevator_set_none+0x48/0xac 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+0x610/0x149c block/blk-mq.c:5119 nbd_start_device+0x158/0xa48 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+0x52c/0xc4c drivers/block/nbd.c:1652 blkdev_ioctl+0x610/0xac0 block/ioctl.c:705 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:598 [inline] __se_sys_ioctl fs/ioctl.c:584 [inline] __arm64_sys_ioctl+0x14c/0x1c4 fs/ioctl.c:584 __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline] invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:49 el0_svc_common+0x130/0x23c arch/arm64/kernel/syscall.c:132 do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:151 el0_svc+0x58/0x180 arch/arm64/kernel/entry-common.c:879 el0t_64_sync_handler+0x84/0x12c arch/arm64/kernel/entry-common.c:898 el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:596