======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.5.9420/31523 is trying to acquire lock:
ffffffff8e025728 (pcpu_alloc_mutex){+.+.}-{4:4}, at: pcpu_alloc_noprof+0x286/0x1720

but task is already holding lock:
ffff8881698a00a8 (&q->q_usage_counter(io)#50){++++}-{0:0}, at: nbd_start_device+0x17f/0xb10

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (&q->q_usage_counter(io)#50){++++}-{0:0}:
       lock_acquire+0x120/0x360
       blk_alloc_queue+0x538/0x620
       __blk_mq_alloc_disk+0x15c/0x340
       nbd_dev_add+0x46c/0xae0
       nbd_init+0x1c6/0x240
       do_one_initcall+0x236/0x820
       do_initcall_level+0x104/0x190
       do_initcalls+0x59/0xa0
       kernel_init_freeable+0x334/0x4b0
       kernel_init+0x1d/0x1d0
       ret_from_fork+0x4bc/0x870
       ret_from_fork_asm+0x1a/0x30

-> #1 (fs_reclaim){+.+.}-{0:0}:
       lock_acquire+0x120/0x360
       fs_reclaim_acquire+0x72/0x100
       prepare_alloc_pages+0x152/0x650
       __alloc_frozen_pages_noprof+0x123/0x370
       __alloc_pages_noprof+0xa/0x30
       pcpu_populate_chunk+0x182/0xb30
       pcpu_alloc_noprof+0xcbf/0x1720
       bpf_map_alloc_percpu+0xbc/0x1b0
       array_map_alloc+0x385/0x700
       map_create+0xaa6/0x1640
       __sys_bpf+0x5f0/0x860
       __x64_sys_bpf+0x7c/0x90
       do_syscall_64+0xfa/0xfa0
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (pcpu_alloc_mutex){+.+.}-{4:4}:
       validate_chain+0xb9b/0x2140
       __lock_acquire+0xab9/0xd20
       lock_acquire+0x120/0x360
       __mutex_lock+0x187/0x1350
       pcpu_alloc_noprof+0x286/0x1720
       sbitmap_init_node+0x1e1/0x640
       sbitmap_queue_init_node+0x3e/0x4d0
       blk_mq_init_tags+0x15c/0x2d0
       blk_mq_alloc_map_and_rqs+0xbb/0x9c0
       blk_mq_update_nr_hw_queues+0xa90/0x1ae0
       nbd_start_device+0x17f/0xb10
       nbd_genl_connect+0x135b/0x18f0
       genl_family_rcv_msg_doit+0x215/0x300
       genl_rcv_msg+0x60e/0x790
       netlink_rcv_skb+0x208/0x470
       genl_rcv+0x28/0x40
       netlink_unicast+0x82f/0x9e0
       netlink_sendmsg+0x805/0xb30
       __sock_sendmsg+0x21c/0x270
       ____sys_sendmsg+0x505/0x830
       ___sys_sendmsg+0x21f/0x2a0
       __x64_sys_sendmsg+0x19b/0x260
       do_syscall_64+0xfa/0xfa0
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

Chain exists of:
  pcpu_alloc_mutex --> fs_reclaim --> &q->q_usage_counter(io)#50

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&q->q_usage_counter(io)#50);
                               lock(fs_reclaim);
                               lock(&q->q_usage_counter(io)#50);
  lock(pcpu_alloc_mutex);

 *** DEADLOCK ***

6 locks held by syz.5.9420/31523:
 #0: ffffffff8f332650 (cb_lock){++++}-{4:4}, at: genl_rcv+0x19/0x40
 #1: ffffffff8f332468 (genl_mutex){+.+.}-{4:4}, at: genl_rcv_msg+0x10d/0x790
 #2: ffff888106b4c1c8 (&set->update_nr_hwq_lock){++++}-{4:4}, at: blk_mq_update_nr_hw_queues+0xa7/0x1ae0
 #3: ffff888106b4c0d8 (&set->tag_list_lock){+.+.}-{4:4}, at: blk_mq_update_nr_hw_queues+0xba/0x1ae0
 #4: ffff8881698a00a8 (&q->q_usage_counter(io)#50){++++}-{0:0}, at: nbd_start_device+0x17f/0xb10
 #5: ffff8881698a00e0 (&q->q_usage_counter(queue)#34){+.+.}-{0:0}, at: nbd_start_device+0x17f/0xb10

stack backtrace:
CPU: 1 UID: 0 PID: 31523 Comm: syz.5.9420 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250
 print_circular_bug+0x2ee/0x310
 check_noncircular+0x134/0x160
 validate_chain+0xb9b/0x2140
 __lock_acquire+0xab9/0xd20
 lock_acquire+0x120/0x360
 __mutex_lock+0x187/0x1350
 pcpu_alloc_noprof+0x286/0x1720
 sbitmap_init_node+0x1e1/0x640
 sbitmap_queue_init_node+0x3e/0x4d0
 blk_mq_init_tags+0x15c/0x2d0
 blk_mq_alloc_map_and_rqs+0xbb/0x9c0
 blk_mq_update_nr_hw_queues+0xa90/0x1ae0
 nbd_start_device+0x17f/0xb10
 nbd_genl_connect+0x135b/0x18f0
 genl_family_rcv_msg_doit+0x215/0x300
 genl_rcv_msg+0x60e/0x790
 netlink_rcv_skb+0x208/0x470
 genl_rcv+0x28/0x40
 netlink_unicast+0x82f/0x9e0
 netlink_sendmsg+0x805/0xb30
 __sock_sendmsg+0x21c/0x270
 ____sys_sendmsg+0x505/0x830
 ___sys_sendmsg+0x21f/0x2a0
 __x64_sys_sendmsg+0x19b/0x260
 do_syscall_64+0xfa/0xfa0
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fdbacd8f749
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:00007fdbadc6a038 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007fdbacfe5fa0 RCX: 00007fdbacd8f749
RDX: 0000000020000000 RSI: 0000200000001ac0 RDI: 0000000000000004
RBP: 00007fdbace13f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fdbacfe6038 R14: 00007fdbacfe5fa0 R15: 00007ffd52bd2678
 </TASK>
