======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.0.759/7631 is trying to acquire lock:
ffffffff8e426ce8 (pcpu_alloc_mutex){+.+.}-{4:4}, at: pcpu_alloc_noprof+0x288/0x18d0

but task is already holding lock:
ffff88810a17e2c8 (&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+0x11f/0x350
       blk_alloc_queue+0x538/0x620
       __blk_mq_alloc_disk+0x197/0x390
       nbd_dev_add+0x499/0xb50
       nbd_init+0x1c6/0x240
       do_one_initcall+0x2ae/0x870
       do_initcall_level+0x104/0x190
       do_initcalls+0x59/0xa0
       kernel_init_freeable+0x34c/0x4c0
       kernel_init+0x1d/0x1d0
       ret_from_fork+0x4d3/0x870
       ret_from_fork_asm+0x1a/0x30

-> #1 (fs_reclaim){+.+.}-{0:0}:
       lock_acquire+0x11f/0x350
       fs_reclaim_acquire+0x71/0x100
       prepare_alloc_pages+0x153/0x610
       __alloc_frozen_pages_noprof+0x12f/0x380
       __alloc_pages_noprof+0xa/0x30
       pcpu_populate_chunk+0x182/0xb20
       pcpu_alloc_noprof+0xc3b/0x18d0
       xt_percpu_counter_alloc+0x161/0x220
       translate_table+0x1332/0x20b0
       ip6t_register_table+0x11b/0x800
       ip6table_mangle_table_init+0x41/0x70
       xt_find_table_lock+0x30c/0x3e0
       xt_request_find_table_lock+0x26/0x100
       do_ip6t_get_ctl+0x716/0x1230
       nf_getsockopt+0x26e/0x290
       ipv6_getsockopt+0x1fd/0x2b0
       do_sock_getsockopt+0x383/0x460
       __x64_sys_getsockopt+0x1a4/0x240
       do_syscall_64+0xf0/0xfa0
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (pcpu_alloc_mutex){+.+.}-{4:4}:
       validate_chain+0xb9a/0x2130
       __lock_acquire+0xab8/0xd20
       lock_acquire+0x11f/0x350
       __mutex_lock+0x19f/0x1300
       pcpu_alloc_noprof+0x288/0x18d0
       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+0xa7b/0x1b30
       nbd_start_device+0x17f/0xb10
       nbd_genl_connect+0x166e/0x1cf0
       genl_family_rcv_msg_doit+0x22a/0x330
       genl_rcv_msg+0x61c/0x7a0
       netlink_rcv_skb+0x232/0x4b0
       genl_rcv+0x28/0x40
       netlink_unicast+0x80f/0x9b0
       netlink_sendmsg+0x813/0xb40
       ____sys_sendmsg+0xa84/0xaf0
       ___sys_sendmsg+0x2a5/0x360
       __x64_sys_sendmsg+0x1bd/0x2a0
       do_syscall_64+0xf0/0xfa0
       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.0.759/7631:
 #0: ffffffff8f73f7f0 (cb_lock){++++}-{4:4}, at: genl_rcv+0x19/0x40
 #1: ffffffff8f73f608 (genl_mutex){+.+.}-{4:4}, at: genl_rcv_msg+0x10b/0x7a0
 #2: ffff88810a29f1c8 (&set->update_nr_hwq_lock){++++}-{4:4}, at: blk_mq_update_nr_hw_queues+0xc4/0x1b30
 #3: ffff88810a29f0d8 (&set->tag_list_lock){+.+.}-{4:4}, at: blk_mq_update_nr_hw_queues+0xd7/0x1b30
 #4: ffff88810a17e2c8 (&q->q_usage_counter(io)#50){++++}-{0:0}, at: nbd_start_device+0x17f/0xb10
 #5: ffff88810a17e300 (&q->q_usage_counter(queue)#34){+.+.}-{0:0}, at: nbd_start_device+0x17f/0xb10

stack backtrace:
CPU: 0 UID: 0 PID: 7631 Comm: syz.0.759 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+0x2ed/0x300
 check_noncircular+0x134/0x160
 validate_chain+0xb9a/0x2130
 __lock_acquire+0xab8/0xd20
 lock_acquire+0x11f/0x350
 __mutex_lock+0x19f/0x1300
 pcpu_alloc_noprof+0x288/0x18d0
 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+0xa7b/0x1b30
 nbd_start_device+0x17f/0xb10
 nbd_genl_connect+0x166e/0x1cf0
 genl_family_rcv_msg_doit+0x22a/0x330
 genl_rcv_msg+0x61c/0x7a0
 netlink_rcv_skb+0x232/0x4b0
 genl_rcv+0x28/0x40
 netlink_unicast+0x80f/0x9b0
 netlink_sendmsg+0x813/0xb40
 ____sys_sendmsg+0xa84/0xaf0
 ___sys_sendmsg+0x2a5/0x360
 __x64_sys_sendmsg+0x1bd/0x2a0
 do_syscall_64+0xf0/0xfa0
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7feddfb9c819
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:00007fede09c0028 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007feddfe15fa0 RCX: 00007feddfb9c819
RDX: 0000000020000810 RSI: 0000200000001ac0 RDI: 0000000000000004
RBP: 00007feddfc32c91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007feddfe16038 R14: 00007feddfe15fa0 R15: 00007ffd51a07a18
 </TASK>
nbd1: detected capacity change from 0 to 127
