WARNING: possible circular locking dependency detected
syzkaller #0 Tainted: G             L     
------------------------------------------------------
syz.7.5187/24138 is trying to acquire lock:
ffff8880250b9828 (&q->elevator_lock){+.+.}-{4:4}, at: queue_requests_store+0x45b/0x5f0 block/blk-sysfs.c:124

but task is already holding lock:
ffff8880250b9300 (&q->q_usage_counter(io)#66){++++}-{0:0}, at: blk_mq_freeze_queue include/linux/blk-mq.h:956 [inline]
ffff8880250b9300 (&q->q_usage_counter(io)#66){++++}-{0:0}, at: queue_requests_store+0x44d/0x5f0 block/blk-sysfs.c:123

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #6 (&q->q_usage_counter(io)#66){++++}-{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
       null_add_dev+0xe82/0x1d70 drivers/block/null_blk/main.c:2017
       null_create_dev drivers/block/null_blk/main.c:2114 [inline]
       null_init+0x1e3/0x390 drivers/block/null_blk/main.c:2178
       do_one_initcall+0x250/0x870 init/main.c:1357
       do_initcall_level+0x10a/0x1a0 init/main.c:1419
       do_initcalls+0x59/0xa0 init/main.c:1435
       kernel_init_freeable+0x29d/0x3e0 init/main.c:1670
       kernel_init+0x22/0x1d0 init/main.c:1560
       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 (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_node_noprof+0x5f/0x610 mm/slub.c:5068
       __alloc_skb+0x1db/0x7a0 net/core/skbuff.c:704
       alloc_skb_fclone include/linux/skbuff.h:1434 [inline]
       tcp_stream_alloc_skb+0x3f/0x580 net/ipv4/tcp.c:931
       tcp_sendmsg_locked+0x138c/0x5400 net/ipv4/tcp.c:1256
       tcp_sendmsg+0x2f/0x50 net/ipv4/tcp.c:1451
       sock_sendmsg_nosec+0x10e/0x180 net/socket.c:801
       __sock_sendmsg net/socket.c:815 [inline]
       sock_write_iter+0x2de/0x3e0 net/socket.c:1266
       new_sync_write fs/read_write.c:595 [inline]
       vfs_write+0x612/0xba0 fs/read_write.c:687
       ksys_write+0x150/0x270 fs/read_write.c:739
       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

-> #4 (sk_lock-AF_INET){+.+.}-{0:0}:
       lock_sock_nested+0x41/0x100 net/core/sock.c:3830
       lock_sock include/net/sock.h:1713 [inline]
       inet_shutdown+0x6a/0x390 net/ipv4/af_inet.c:913
       nbd_mark_nsock_dead+0x2cb/0x550 drivers/block/nbd.c:319
       recv_work+0x1cee/0x1e10 drivers/block/nbd.c:1030
       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

-> #3 (&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

-> #2 (&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

-> #1 (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:1357
       do_initcall_level+0x10a/0x1a0 init/main.c:1419
       do_initcalls+0x59/0xa0 init/main.c:1435
       kernel_init_freeable+0x29d/0x3e0 init/main.c:1670
       kernel_init+0x22/0x1d0 init/main.c:1560
       ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
       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: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
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x19d/0x1550 kernel/locking/mutex.c:821
       queue_requests_store+0x45b/0x5f0 block/blk-sysfs.c:124
       queue_attr_store+0x207/0x2b0 block/blk-sysfs.c:906
       kernfs_fop_write_iter+0x3a4/0x540 fs/kernfs/file.c:345
       do_iter_readv_writev+0x612/0x8c0 fs/read_write.c:-1
       vfs_writev+0x343/0x990 fs/read_write.c:1058
       do_writev+0x154/0x2e0 fs/read_write.c:1104
       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:
  &q->elevator_lock --> fs_reclaim --> &q->q_usage_counter(io)#66

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&q->q_usage_counter(io)#66);
                               lock(fs_reclaim);
                               lock(&q->q_usage_counter(io)#66);
  lock(&q->elevator_lock);

 *** DEADLOCK ***

locks held by syz.7.5187/24138: 7, last CPU#0:
 #0: ffff88807f8355f0 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x246/0x320 fs/file.c:1259
 #1: ffff8880687a8460 (sb_writers#7){.+.+}-{0:0}, at: file_start_write include/linux/fs.h:2753 [inline]
 #1: ffff8880687a8460 (sb_writers#7){.+.+}-{0:0}, at: vfs_writev+0x2af/0x990 fs/read_write.c:1056
 #2: ffff888026ad4080 (&of->mutex){+.+.}-{4:4}, at: kernfs_fop_write_iter+0x1d8/0x540 fs/kernfs/file.c:336
 #3: ffff888027389698 (kn->active#73){.+.+}-{0:0}, at: kernfs_get_active_of fs/kernfs/file.c:73 [inline]
 #3: ffff888027389698 (kn->active#73){.+.+}-{0:0}, at: kernfs_fop_write_iter+0x22b/0x540 fs/kernfs/file.c:337
 #4: ffff8880237851f8 (&set->update_nr_hwq_lock){++++}-{4:4}, at: queue_requests_store+0x19d/0x5f0 block/blk-sysfs.c:88
 #5: ffff8880250b9300 (&q->q_usage_counter(io)#66){++++}-{0:0}, at: blk_mq_freeze_queue include/linux/blk-mq.h:956 [inline]
 #5: ffff8880250b9300 (&q->q_usage_counter(io)#66){++++}-{0:0}, at: queue_requests_store+0x44d/0x5f0 block/blk-sysfs.c:123
 #6: ffff8880250b9338 (&q->q_usage_counter(queue)#49){+.+.}-{0:0}, at: blk_mq_freeze_queue include/linux/blk-mq.h:956 [inline]
 #6: ffff8880250b9338 (&q->q_usage_counter(queue)#49){+.+.}-{0:0}, at: queue_requests_store+0x44d/0x5f0 block/blk-sysfs.c:123

stack backtrace:
CPU: 0 UID: 0 PID: 24138 Comm: syz.7.5187 Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/26/2026
Call Trace:
 <TASK>
 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
 __mutex_lock_common kernel/locking/mutex.c:646 [inline]
 __mutex_lock+0x19d/0x1550 kernel/locking/mutex.c:821
 queue_requests_store+0x45b/0x5f0 block/blk-sysfs.c:124
 queue_attr_store+0x207/0x2b0 block/blk-sysfs.c:906
 kernfs_fop_write_iter+0x3a4/0x540 fs/kernfs/file.c:345
 do_iter_readv_writev+0x612/0x8c0 fs/read_write.c:-1
 vfs_writev+0x343/0x990 fs/read_write.c:1058
 do_writev+0x154/0x2e0 fs/read_write.c:1104
 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: 0033:0x7fd1cd19e159
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:00007fd1ce0b8028 EFLAGS: 00000246 ORIG_RAX: 0000000000000014
RAX: ffffffffffffffda RBX: 00007fd1cd425fa0 RCX: 00007fd1cd19e159
RDX: 0000000000000002 RSI: 0000200000000000 RDI: 0000000000000005
RBP: 00007fd1cd23503b R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fd1cd426038 R14: 00007fd1cd425fa0 R15: 00007ffe8ab07048
 </TASK>