====================================================== WARNING: possible circular locking dependency detected 6.15.0-rc4-syzkaller-00296-ge8ab83e34bdc #0 Not tainted ------------------------------------------------------ syz.6.3948/19248 is trying to acquire lock: ffff8881433f7118 (&q->elevator_lock){+.+.}-{4:4}, at: blk_mq_elv_switch_none block/blk-mq.c:4951 [inline] ffff8881433f7118 (&q->elevator_lock){+.+.}-{4:4}, at: __blk_mq_update_nr_hw_queues block/blk-mq.c:5031 [inline] ffff8881433f7118 (&q->elevator_lock){+.+.}-{4:4}, at: blk_mq_update_nr_hw_queues+0x49a/0x1a10 block/blk-mq.c:5083 but task is already holding lock: ffff8881433f6be8 (&q->q_usage_counter(io)#55){++++}-{0:0}, at: nbd_start_device+0x16c/0xac0 drivers/block/nbd.c:1476 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #2 (&q->q_usage_counter(io)#55){++++}-{0:0}: lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5866 blk_alloc_queue+0x538/0x620 block/blk-core.c:461 blk_mq_alloc_queue block/blk-mq.c:4348 [inline] __blk_mq_alloc_disk+0x164/0x350 block/blk-mq.c:4395 nbd_dev_add+0x478/0xb10 drivers/block/nbd.c:1933 nbd_init+0x21a/0x2d0 drivers/block/nbd.c:2670 do_one_initcall+0x236/0x820 init/main.c:1257 do_initcall_level+0x137/0x1f0 init/main.c:1319 do_initcalls+0x69/0xd0 init/main.c:1335 kernel_init_freeable+0x3d9/0x570 init/main.c:1567 kernel_init+0x1d/0x1d0 init/main.c:1457 ret_from_fork+0x4e/0x80 arch/x86/kernel/process.c:153 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:5866 __fs_reclaim_acquire mm/page_alloc.c:4064 [inline] fs_reclaim_acquire+0x72/0x100 mm/page_alloc.c:4078 might_alloc include/linux/sched/mm.h:318 [inline] slab_pre_alloc_hook mm/slub.c:4098 [inline] slab_alloc_node mm/slub.c:4176 [inline] kmem_cache_alloc_noprof+0x44/0x3c0 mm/slub.c:4203 __kernfs_new_node+0xd7/0x7f0 fs/kernfs/dir.c:637 kernfs_new_node+0x102/0x210 fs/kernfs/dir.c:713 kernfs_create_dir_ns+0x44/0x130 fs/kernfs/dir.c:1081 sysfs_create_dir_ns+0x123/0x280 fs/sysfs/dir.c:59 create_dir lib/kobject.c:73 [inline] kobject_add_internal+0x59f/0xb40 lib/kobject.c:240 kobject_add_varg lib/kobject.c:374 [inline] kobject_add+0x155/0x220 lib/kobject.c:426 elv_register_queue+0xdb/0x260 block/elevator.c:462 blk_register_queue+0x375/0x450 block/blk-sysfs.c:874 add_disk_fwnode+0x77f/0x10e0 block/genhd.c:505 add_disk include/linux/blkdev.h:757 [inline] nbd_dev_add+0x710/0xb10 drivers/block/nbd.c:1963 nbd_init+0x21a/0x2d0 drivers/block/nbd.c:2670 do_one_initcall+0x236/0x820 init/main.c:1257 do_initcall_level+0x137/0x1f0 init/main.c:1319 do_initcalls+0x69/0xd0 init/main.c:1335 kernel_init_freeable+0x3d9/0x570 init/main.c:1567 kernel_init+0x1d/0x1d0 init/main.c:1457 ret_from_fork+0x4e/0x80 arch/x86/kernel/process.c:153 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 -> #0 (&q->elevator_lock){+.+.}-{4:4}: check_prev_add kernel/locking/lockdep.c:3166 [inline] check_prevs_add kernel/locking/lockdep.c:3285 [inline] validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3909 __lock_acquire+0xaac/0xd20 kernel/locking/lockdep.c:5235 lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5866 __mutex_lock_common kernel/locking/mutex.c:601 [inline] __mutex_lock+0x182/0xe80 kernel/locking/mutex.c:746 blk_mq_elv_switch_none block/blk-mq.c:4951 [inline] __blk_mq_update_nr_hw_queues block/blk-mq.c:5031 [inline] blk_mq_update_nr_hw_queues+0x49a/0x1a10 block/blk-mq.c:5083 nbd_start_device+0x16c/0xac0 drivers/block/nbd.c:1476 nbd_start_device_ioctl drivers/block/nbd.c:1527 [inline] __nbd_ioctl drivers/block/nbd.c:1602 [inline] nbd_ioctl+0x636/0xeb0 drivers/block/nbd.c:1642 blkdev_ioctl+0x5a8/0x6d0 block/ioctl.c:704 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:906 [inline] __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:892 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xf6/0x210 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: &q->elevator_lock --> fs_reclaim --> &q->q_usage_counter(io)#55 Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&q->q_usage_counter(io)#55); lock(fs_reclaim); lock(&q->q_usage_counter(io)#55); lock(&q->elevator_lock); *** DEADLOCK *** 4 locks held by syz.6.3948/19248: #0: ffff888024d15998 (&nbd->config_lock){+.+.}-{4:4}, at: nbd_ioctl+0x131/0xeb0 drivers/block/nbd.c:1635 #1: ffff888024d158d8 (&set->tag_list_lock){+.+.}-{4:4}, at: blk_mq_update_nr_hw_queues+0xac/0x1a10 block/blk-mq.c:5082 #2: ffff8881433f6be8 (&q->q_usage_counter(io)#55){++++}-{0:0}, at: nbd_start_device+0x16c/0xac0 drivers/block/nbd.c:1476 #3: ffff8881433f6c20 (&q->q_usage_counter(queue)#7){+.+.}-{0:0}, at: nbd_start_device+0x16c/0xac0 drivers/block/nbd.c:1476 stack backtrace: CPU: 0 UID: 0 PID: 19248 Comm: syz.6.3948 Not tainted 6.15.0-rc4-syzkaller-00296-ge8ab83e34bdc #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/29/2025 Call Trace: dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120 print_circular_bug+0x2ee/0x310 kernel/locking/lockdep.c:2079 check_noncircular+0x134/0x160 kernel/locking/lockdep.c:2211 check_prev_add kernel/locking/lockdep.c:3166 [inline] check_prevs_add kernel/locking/lockdep.c:3285 [inline] validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3909 __lock_acquire+0xaac/0xd20 kernel/locking/lockdep.c:5235 lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5866 __mutex_lock_common kernel/locking/mutex.c:601 [inline] __mutex_lock+0x182/0xe80 kernel/locking/mutex.c:746 blk_mq_elv_switch_none block/blk-mq.c:4951 [inline] __blk_mq_update_nr_hw_queues block/blk-mq.c:5031 [inline] blk_mq_update_nr_hw_queues+0x49a/0x1a10 block/blk-mq.c:5083 nbd_start_device+0x16c/0xac0 drivers/block/nbd.c:1476 nbd_start_device_ioctl drivers/block/nbd.c:1527 [inline] __nbd_ioctl drivers/block/nbd.c:1602 [inline] nbd_ioctl+0x636/0xeb0 drivers/block/nbd.c:1642 blkdev_ioctl+0x5a8/0x6d0 block/ioctl.c:704 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:906 [inline] __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:892 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xf6/0x210 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7ff9bd98e969 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:00007ff9be788038 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 RAX: ffffffffffffffda RBX: 00007ff9bdbb6080 RCX: 00007ff9bd98e969 RDX: 0000000000000000 RSI: 000000000000ab03 RDI: 0000000000000004 RBP: 00007ff9bda10ab1 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 R13: 0000000000000001 R14: 00007ff9bdbb6080 R15: 00007ffecf0102d8 block nbd6: shutting down sockets