======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.0.4483/16227 is trying to acquire lock:
ffffffff8e453028 (pcpu_alloc_mutex){+.+.}-{4:4}, at: pcpu_alloc_noprof+0x260/0x1970

but task is already holding lock:
ffff888109bce938 (&q->q_usage_counter(io)#51){++++}-{0:0}, at: nbd_start_device+0x189/0xb30

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (&q->q_usage_counter(io)#51){++++}-{0:0}:
       blk_alloc_queue+0x53e/0x630
       __blk_mq_alloc_disk+0x194/0x390
       nbd_dev_add+0x494/0xb60
       nbd_init+0x15f/0x1e0
       do_one_initcall+0x256/0x880
       do_initcall_level+0x10a/0x1a0
       do_initcalls+0x59/0xa0
       kernel_init_freeable+0x32f/0x4b0
       kernel_init+0x1d/0x1d0
       ret_from_fork+0x5b0/0xb20
       ret_from_fork_asm+0x1a/0x30

-> #1 (fs_reclaim){+.+.}-{0:0}:
       fs_reclaim_acquire+0x71/0x100
       prepare_alloc_pages+0x15b/0x650
       __alloc_frozen_pages_noprof+0x12f/0x380
       __alloc_pages_noprof+0xa/0x30
       pcpu_populate_chunk+0x181/0xb30
       pcpu_alloc_noprof+0xc83/0x1970
       bpf_map_alloc_percpu+0xbb/0x1b0
       prealloc_init+0x214/0x650
       htab_map_alloc+0x6a0/0xc90
       map_create+0xaa3/0x1660
       __sys_bpf+0x65b/0x920
       __x64_sys_bpf+0x7c/0x90
       do_syscall_64+0xf0/0xf80
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (pcpu_alloc_mutex){+.+.}-{4:4}:
       __lock_acquire+0x1520/0x2cd0
       lock_acquire+0x116/0x340
       __mutex_lock+0x199/0x12d0
       pcpu_alloc_noprof+0x260/0x1970
       sbitmap_init_node+0x1dc/0x630
       sbitmap_queue_init_node+0x3e/0x4d0
       blk_mq_init_tags+0x15c/0x2d0
       blk_mq_alloc_map_and_rqs+0xc8/0x9d0
       blk_mq_update_nr_hw_queues+0xa32/0x1a70
       nbd_start_device+0x189/0xb30
       nbd_genl_connect+0x1597/0x1c10
       genl_family_rcv_msg_doit+0x233/0x340
       genl_rcv_msg+0x614/0x7a0
       netlink_rcv_skb+0x226/0x4a0
       genl_rcv+0x28/0x40
       netlink_unicast+0x833/0x9f0
       netlink_sendmsg+0x813/0xb40
       ____sys_sendmsg+0xa67/0xad0
       ___sys_sendmsg+0x2a5/0x360
       __x64_sys_sendmsg+0x1bd/0x2a0
       do_syscall_64+0xf0/0xf80
       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)#51

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&q->q_usage_counter(io)#51);
                               lock(fs_reclaim);
                               lock(&q->q_usage_counter(io)#51);
  lock(pcpu_alloc_mutex);

 *** DEADLOCK ***

6 locks held by syz.0.4483/16227:
 #0: ffffffff8f7b3810 (cb_lock){++++}-{4:4}, at: genl_rcv+0x19/0x40
 #1: ffffffff8f7b3628 (genl_mutex){+.+.}-{4:4}, at: genl_rcv_msg+0x10b/0x7a0
 #2: ffff888109e649d0 (&set->update_nr_hwq_lock){++++}-{4:4}, at: blk_mq_update_nr_hw_queues+0xab/0x1a70
 #3: ffff888109e648d8 (&set->tag_list_lock){+.+.}-{4:4}, at: blk_mq_update_nr_hw_queues+0xbe/0x1a70
 #4: ffff888109bce938 (&q->q_usage_counter(io)#51){++++}-{0:0}, at: nbd_start_device+0x189/0xb30
 #5: ffff888109bce970 (&q->q_usage_counter(queue)#35){+.+.}-{0:0}, at: nbd_start_device+0x189/0xb30

stack backtrace:
CPU: 1 UID: 0 PID: 16227 Comm: syz.0.4483 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+0x1a9/0x280
 print_circular_bug+0x2e1/0x300
 check_noncircular+0x12e/0x150
 __lock_acquire+0x1520/0x2cd0
 lock_acquire+0x116/0x340
 __mutex_lock+0x199/0x12d0
 pcpu_alloc_noprof+0x260/0x1970
 sbitmap_init_node+0x1dc/0x630
 sbitmap_queue_init_node+0x3e/0x4d0
 blk_mq_init_tags+0x15c/0x2d0
 blk_mq_alloc_map_and_rqs+0xc8/0x9d0
 blk_mq_update_nr_hw_queues+0xa32/0x1a70
 nbd_start_device+0x189/0xb30
 nbd_genl_connect+0x1597/0x1c10
 genl_family_rcv_msg_doit+0x233/0x340
 genl_rcv_msg+0x614/0x7a0
 netlink_rcv_skb+0x226/0x4a0
 genl_rcv+0x28/0x40
 netlink_unicast+0x833/0x9f0
 netlink_sendmsg+0x813/0xb40
 ____sys_sendmsg+0xa67/0xad0
 ___sys_sendmsg+0x2a5/0x360
 __x64_sys_sendmsg+0x1bd/0x2a0
 do_syscall_64+0xf0/0xf80
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fc76279ce59
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:00007fc7635f3028 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007fc762a15fa0 RCX: 00007fc76279ce59
RDX: 0000000000000004 RSI: 0000200000001ac0 RDI: 0000000000000007
RBP: 00007fc762832e6f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fc762a16038 R14: 00007fc762a15fa0 R15: 00007ffcd729cbb8
 </TASK>
