======================================================
WARNING: possible circular locking dependency detected
6.17.0-rc1-syzkaller-g8f5ae30d69d7 #0 Not tainted
------------------------------------------------------
syz.3.197/7482 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:
ffff0000ca46bb58 (&q->q_usage_counter(io)#33){++++}-{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)#33){++++}-{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_genl_connect+0xf88/0x158c drivers/block/nbd.c:2228
       genl_family_rcv_msg_doit+0x1d8/0x2bc net/netlink/genetlink.c:1115
       genl_family_rcv_msg net/netlink/genetlink.c:1195 [inline]
       genl_rcv_msg+0x450/0x624 net/netlink/genetlink.c:1210
       netlink_rcv_skb+0x220/0x3fc net/netlink/af_netlink.c:2552
       genl_rcv+0x38/0x50 net/netlink/genetlink.c:1219
       netlink_unicast_kernel net/netlink/af_netlink.c:1320 [inline]
       netlink_unicast+0x694/0x8c4 net/netlink/af_netlink.c:1346
       netlink_sendmsg+0x648/0x930 net/netlink/af_netlink.c:1896
       sock_sendmsg_nosec net/socket.c:714 [inline]
       __sock_sendmsg net/socket.c:729 [inline]
       ____sys_sendmsg+0x490/0x7b8 net/socket.c:2614
       ___sys_sendmsg+0x204/0x278 net/socket.c:2668
       __sys_sendmsg net/socket.c:2700 [inline]
       __do_sys_sendmsg net/socket.c:2705 [inline]
       __se_sys_sendmsg net/socket.c:2703 [inline]
       __arm64_sys_sendmsg+0x184/0x238 net/socket.c:2703
       __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)#33

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&q->q_usage_counter(io)#33);
                               lock(fs_reclaim);
                               lock(&q->q_usage_counter(io)#33);
  lock(&root->kernfs_rwsem);

 *** DEADLOCK ***

6 locks held by syz.3.197/7482:
 #0: ffff800092abd030 (cb_lock){++++}-{4:4}, at: genl_rcv+0x28/0x50 net/netlink/genetlink.c:1218
 #1: ffff800092abce48 (genl_mutex){+.+.}-{4:4}, at: genl_lock net/netlink/genetlink.c:35 [inline]
 #1: ffff800092abce48 (genl_mutex){+.+.}-{4:4}, at: genl_op_lock net/netlink/genetlink.c:60 [inline]
 #1: ffff800092abce48 (genl_mutex){+.+.}-{4:4}, at: genl_rcv_msg+0xf4/0x624 net/netlink/genetlink.c:1209
 #2: ffff0000ca50b188 (&set->update_nr_hwq_lock){++++}-{4:4}, at: blk_mq_update_nr_hw_queues+0x98/0x149c block/blk-mq.c:5117
 #3: ffff0000ca50b0d8 (&set->tag_list_lock){+.+.}-{4:4}, at: blk_mq_update_nr_hw_queues+0xa4/0x149c block/blk-mq.c:5118
 #4: ffff0000ca46bb58 (&q->q_usage_counter(io)#33){++++}-{0:0}, at: nbd_start_device+0x158/0xa48 drivers/block/nbd.c:1478
 #5: ffff0000ca46bb90 (&q->q_usage_counter(queue)){+.+.}-{0:0}, at: nbd_start_device+0x158/0xa48 drivers/block/nbd.c:1478

stack backtrace:
CPU: 1 UID: 0 PID: 7482 Comm: syz.3.197 Not tainted 6.17.0-rc1-syzkaller-g8f5ae30d69d7 #0 PREEMPT 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/30/2025
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_genl_connect+0xf88/0x158c drivers/block/nbd.c:2228
 genl_family_rcv_msg_doit+0x1d8/0x2bc net/netlink/genetlink.c:1115
 genl_family_rcv_msg net/netlink/genetlink.c:1195 [inline]
 genl_rcv_msg+0x450/0x624 net/netlink/genetlink.c:1210
 netlink_rcv_skb+0x220/0x3fc net/netlink/af_netlink.c:2552
 genl_rcv+0x38/0x50 net/netlink/genetlink.c:1219
 netlink_unicast_kernel net/netlink/af_netlink.c:1320 [inline]
 netlink_unicast+0x694/0x8c4 net/netlink/af_netlink.c:1346
 netlink_sendmsg+0x648/0x930 net/netlink/af_netlink.c:1896
 sock_sendmsg_nosec net/socket.c:714 [inline]
 __sock_sendmsg net/socket.c:729 [inline]
 ____sys_sendmsg+0x490/0x7b8 net/socket.c:2614
 ___sys_sendmsg+0x204/0x278 net/socket.c:2668
 __sys_sendmsg net/socket.c:2700 [inline]
 __do_sys_sendmsg net/socket.c:2705 [inline]
 __se_sys_sendmsg net/socket.c:2703 [inline]
 __arm64_sys_sendmsg+0x184/0x238 net/socket.c:2703
 __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