======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.6.2942/20592 is trying to acquire lock:
ffffffff8e21e8e8 (pcpu_alloc_mutex){+.+.}-{4:4}, at: pcpu_alloc_noprof+0x286/0x1720

but task is already holding lock:
ffff8881083c8a78 (&q->q_usage_counter(io)#55){++++}-{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)#55){++++}-{0:0}:
       lock_acquire+0x120/0x360
       blk_alloc_queue+0x538/0x620
       __blk_mq_alloc_disk+0x15c/0x340
       nbd_dev_add+0x46c/0xae0
       nbd_init+0x168/0x1f0
       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+0x439/0x7d0
       ret_from_fork_asm+0x1a/0x30

-> #1 (fs_reclaim){+.+.}-{0:0}:
       lock_acquire+0x120/0x360
       fs_reclaim_acquire+0x72/0x100
       prepare_alloc_pages+0x153/0x610
       __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+0xaa3/0x14d0
       __sys_bpf+0x60f/0x870
       __x64_sys_bpf+0x7c/0x90
       do_syscall_64+0xfa/0x3b0
       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+0x1e1/0x630
       sbitmap_queue_init_node+0x3e/0x4d0
       blk_mq_init_tags+0x110/0x280
       blk_mq_alloc_map_and_rqs+0xbd/0x9f0
       blk_mq_update_nr_hw_queues+0xa26/0x1aa0
       nbd_start_device+0x17f/0xb10
       nbd_ioctl+0x636/0xeb0
       blkdev_ioctl+0x5a8/0x6d0
       __se_sys_ioctl+0xfc/0x170
       do_syscall_64+0xfa/0x3b0
       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)#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(pcpu_alloc_mutex);

 *** DEADLOCK ***

4 locks held by syz.6.2942/20592:
 #0: ffff888108381188 (&set->update_nr_hwq_lock){++++}-{4:4}, at: blk_mq_update_nr_hw_queues+0xa7/0x1aa0
 #1: ffff8881083810d8 (&set->tag_list_lock){+.+.}-{4:4}, at: blk_mq_update_nr_hw_queues+0xba/0x1aa0
 #2: ffff8881083c8a78 (&q->q_usage_counter(io)#55){++++}-{0:0}, at: nbd_start_device+0x17f/0xb10
 #3: ffff8881083c8ab0 (&q->q_usage_counter(queue)#39){+.+.}-{0:0}, at: nbd_start_device+0x17f/0xb10

stack backtrace:
CPU: 1 UID: 0 PID: 20592 Comm: syz.6.2942 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+0x1e1/0x630
 sbitmap_queue_init_node+0x3e/0x4d0
 blk_mq_init_tags+0x110/0x280
 blk_mq_alloc_map_and_rqs+0xbd/0x9f0
 blk_mq_update_nr_hw_queues+0xa26/0x1aa0
 nbd_start_device+0x17f/0xb10
 nbd_ioctl+0x636/0xeb0
 blkdev_ioctl+0x5a8/0x6d0
 __se_sys_ioctl+0xfc/0x170
 do_syscall_64+0xfa/0x3b0
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f1d79d8ec29
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:00007f1d7ab36038 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f1d79fd6090 RCX: 00007f1d79d8ec29
RDX: 0000000000000000 RSI: 000000000000ab03 RDI: 0000000000000004
RBP: 00007f1d79e11e41 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f1d79fd6128 R14: 00007f1d79fd6090 R15: 00007fffd34ad088
 </TASK>
block nbd6: shutting down sockets
