======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.0.17/6040 is trying to acquire lock:
ffffffff8e42bb68 (pcpu_alloc_mutex){+.+.}-{4:4}, at: pcpu_alloc_noprof+0x25b/0x1750 mm/percpu.c:1782

but task is already holding lock:
ffff88802547d628 (&q->q_usage_counter(io)#49){++++}-{0:0}, at: nbd_start_device+0x17f/0xb10 drivers/block/nbd.c:1489

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (&q->q_usage_counter(io)#49){++++}-{0:0}:
       blk_alloc_queue+0x52f/0x610 block/blk-core.c:461
       blk_mq_alloc_queue block/blk-mq.c:4415 [inline]
       __blk_mq_alloc_disk+0x15c/0x340 block/blk-mq.c:4462
       nbd_dev_add+0x46c/0xae0 drivers/block/nbd.c:1954
       nbd_init+0x168/0x1f0 drivers/block/nbd.c:2692
       do_one_initcall+0x1fb/0x820 init/main.c:1380
       do_initcall_level+0x104/0x190 init/main.c:1442
       do_initcalls+0x59/0xa0 init/main.c:1458
       kernel_init_freeable+0x334/0x4b0 init/main.c:1690
       kernel_init+0x1d/0x1d0 init/main.c:1580
       ret_from_fork+0x599/0xb30 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246

-> #1 (fs_reclaim){+.+.}-{0:0}:
       __fs_reclaim_acquire mm/page_alloc.c:4301 [inline]
       fs_reclaim_acquire+0x72/0x100 mm/page_alloc.c:4315
       might_alloc include/linux/sched/mm.h:317 [inline]
       prepare_alloc_pages+0x152/0x650 mm/page_alloc.c:4978
       __alloc_frozen_pages_noprof+0x123/0x370 mm/page_alloc.c:5199
       __alloc_pages_noprof+0xa/0x30 mm/page_alloc.c:5244
       __alloc_pages_node_noprof include/linux/gfp.h:285 [inline]
       alloc_pages_node_noprof include/linux/gfp.h:312 [inline]
       pcpu_alloc_pages mm/percpu-vm.c:95 [inline]
       pcpu_populate_chunk+0x182/0xb30 mm/percpu-vm.c:285
       pcpu_alloc_noprof+0xcb6/0x1750 mm/percpu.c:1870
       xt_percpu_counter_alloc+0x161/0x220 net/netfilter/x_tables.c:1934
       find_check_entry net/ipv4/netfilter/ip_tables.c:526 [inline]
       translate_table+0x12e9/0x2000 net/ipv4/netfilter/ip_tables.c:716
       ipt_register_table+0x106/0x7c0 net/ipv4/netfilter/ip_tables.c:1742
       iptable_security_table_init+0x41/0x70 net/ipv4/netfilter/iptable_security.c:46
       xt_find_table_lock+0x30c/0x3e0 net/netfilter/x_tables.c:1260
       xt_request_find_table_lock+0x26/0x100 net/netfilter/x_tables.c:1285
       get_info net/ipv4/netfilter/ip_tables.c:963 [inline]
       do_ipt_get_ctl+0x730/0x1180 net/ipv4/netfilter/ip_tables.c:1659
       nf_getsockopt+0x26e/0x290 net/netfilter/nf_sockopt.c:116
       ip_getsockopt+0x1c4/0x220 net/ipv4/ip_sockglue.c:1777
       do_sock_getsockopt+0x2b4/0x3d0 net/socket.c:2398
       __sys_getsockopt net/socket.c:2427 [inline]
       __do_sys_getsockopt net/socket.c:2434 [inline]
       __se_sys_getsockopt net/socket.c:2431 [inline]
       __x64_sys_getsockopt+0x1a5/0x250 net/socket.c:2431
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0xf80 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (pcpu_alloc_mutex){+.+.}-{4:4}:
       check_prev_add kernel/locking/lockdep.c:3165 [inline]
       check_prevs_add kernel/locking/lockdep.c:3284 [inline]
       validate_chain kernel/locking/lockdep.c:3908 [inline]
       __lock_acquire+0x15a6/0x2cf0 kernel/locking/lockdep.c:5237
       lock_acquire+0x117/0x340 kernel/locking/lockdep.c:5868
       __mutex_lock_common kernel/locking/mutex.c:614 [inline]
       __mutex_lock+0x187/0x1350 kernel/locking/mutex.c:776
       pcpu_alloc_noprof+0x25b/0x1750 mm/percpu.c:1782
       init_alloc_hint lib/sbitmap.c:16 [inline]
       sbitmap_init_node+0x1e1/0x640 lib/sbitmap.c:126
       sbitmap_queue_init_node+0x3e/0x4d0 lib/sbitmap.c:454
       bt_alloc block/blk-mq-tag.c:546 [inline]
       blk_mq_init_tags+0x15c/0x2d0 block/blk-mq-tag.c:571
       blk_mq_alloc_rq_map block/blk-mq.c:3546 [inline]
       blk_mq_alloc_map_and_rqs+0xbb/0x9c0 block/blk-mq.c:4114
       __blk_mq_alloc_map_and_rqs block/blk-mq.c:4136 [inline]
       blk_mq_realloc_tag_set_tags block/blk-mq.c:4803 [inline]
       __blk_mq_update_nr_hw_queues block/blk-mq.c:5134 [inline]
       blk_mq_update_nr_hw_queues+0xa2f/0x1a80 block/blk-mq.c:5186
       nbd_start_device+0x17f/0xb10 drivers/block/nbd.c:1489
       nbd_genl_connect+0x1353/0x1900 drivers/block/nbd.c:2239
       genl_family_rcv_msg_doit+0x215/0x300 net/netlink/genetlink.c:1115
       genl_family_rcv_msg net/netlink/genetlink.c:1195 [inline]
       genl_rcv_msg+0x60e/0x790 net/netlink/genetlink.c:1210
       netlink_rcv_skb+0x208/0x470 net/netlink/af_netlink.c:2550
       genl_rcv+0x28/0x40 net/netlink/genetlink.c:1219
       netlink_unicast_kernel net/netlink/af_netlink.c:1318 [inline]
       netlink_unicast+0x82f/0x9e0 net/netlink/af_netlink.c:1344
       netlink_sendmsg+0x805/0xb30 net/netlink/af_netlink.c:1894
       sock_sendmsg_nosec+0x18f/0x1d0 net/socket.c:737
       __sock_sendmsg net/socket.c:752 [inline]
       ____sys_sendmsg+0x577/0x880 net/socket.c:2610
       ___sys_sendmsg+0x21f/0x2a0 net/socket.c:2664
       __sys_sendmsg net/socket.c:2696 [inline]
       __do_sys_sendmsg net/socket.c:2701 [inline]
       __se_sys_sendmsg net/socket.c:2699 [inline]
       __x64_sys_sendmsg+0x19b/0x260 net/socket.c:2699
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0xf80 arch/x86/entry/syscall_64.c:94
       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)#49

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&q->q_usage_counter(io)#49);
                               lock(fs_reclaim);
                               lock(&q->q_usage_counter(io)#49);
  lock(pcpu_alloc_mutex);

 *** DEADLOCK ***

6 locks held by syz.0.17/6040:
 #0: ffffffff8f794230 (cb_lock){++++}-{4:4}, at: genl_rcv+0x19/0x40 net/netlink/genetlink.c:1218
 #1: ffffffff8f794048 (genl_mutex){+.+.}-{4:4}, at: genl_lock net/netlink/genetlink.c:35 [inline]
 #1: ffffffff8f794048 (genl_mutex){+.+.}-{4:4}, at: genl_op_lock net/netlink/genetlink.c:60 [inline]
 #1: ffffffff8f794048 (genl_mutex){+.+.}-{4:4}, at: genl_rcv_msg+0x10d/0x790 net/netlink/genetlink.c:1209
 #2: ffff8880255401d0 (&set->update_nr_hwq_lock){++++}-{4:4}, at: blk_mq_update_nr_hw_queues+0xa6/0x1a80 block/blk-mq.c:5184
 #3: ffff8880255400d8 (&set->tag_list_lock){+.+.}-{4:4}, at: blk_mq_update_nr_hw_queues+0xb9/0x1a80 block/blk-mq.c:5185
 #4: ffff88802547d628 (&q->q_usage_counter(io)#49){++++}-{0:0}, at: nbd_start_device+0x17f/0xb10 drivers/block/nbd.c:1489
 #5: ffff88802547d660 (&q->q_usage_counter(queue)#33){+.+.}-{0:0}, at: nbd_start_device+0x17f/0xb10 drivers/block/nbd.c:1489

stack backtrace:
CPU: 0 UID: 0 PID: 6040 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 print_circular_bug+0x2e2/0x300 kernel/locking/lockdep.c:2043
 check_noncircular+0x12e/0x150 kernel/locking/lockdep.c:2175
 check_prev_add kernel/locking/lockdep.c:3165 [inline]
 check_prevs_add kernel/locking/lockdep.c:3284 [inline]
 validate_chain kernel/locking/lockdep.c:3908 [inline]
 __lock_acquire+0x15a6/0x2cf0 kernel/locking/lockdep.c:5237
 lock_acquire+0x117/0x340 kernel/locking/lockdep.c:5868
 __mutex_lock_common kernel/locking/mutex.c:614 [inline]
 __mutex_lock+0x187/0x1350 kernel/locking/mutex.c:776
 pcpu_alloc_noprof+0x25b/0x1750 mm/percpu.c:1782
 init_alloc_hint lib/sbitmap.c:16 [inline]
 sbitmap_init_node+0x1e1/0x640 lib/sbitmap.c:126
 sbitmap_queue_init_node+0x3e/0x4d0 lib/sbitmap.c:454
 bt_alloc block/blk-mq-tag.c:546 [inline]
 blk_mq_init_tags+0x15c/0x2d0 block/blk-mq-tag.c:571
 blk_mq_alloc_rq_map block/blk-mq.c:3546 [inline]
 blk_mq_alloc_map_and_rqs+0xbb/0x9c0 block/blk-mq.c:4114
 __blk_mq_alloc_map_and_rqs block/blk-mq.c:4136 [inline]
 blk_mq_realloc_tag_set_tags block/blk-mq.c:4803 [inline]
 __blk_mq_update_nr_hw_queues block/blk-mq.c:5134 [inline]
 blk_mq_update_nr_hw_queues+0xa2f/0x1a80 block/blk-mq.c:5186
 nbd_start_device+0x17f/0xb10 drivers/block/nbd.c:1489
 nbd_genl_connect+0x1353/0x1900 drivers/block/nbd.c:2239
 genl_family_rcv_msg_doit+0x215/0x300 net/netlink/genetlink.c:1115
 genl_family_rcv_msg net/netlink/genetlink.c:1195 [inline]
 genl_rcv_msg+0x60e/0x790 net/netlink/genetlink.c:1210
 netlink_rcv_skb+0x208/0x470 net/netlink/af_netlink.c:2550
 genl_rcv+0x28/0x40 net/netlink/genetlink.c:1219
 netlink_unicast_kernel net/netlink/af_netlink.c:1318 [inline]
 netlink_unicast+0x82f/0x9e0 net/netlink/af_netlink.c:1344
 netlink_sendmsg+0x805/0xb30 net/netlink/af_netlink.c:1894
 sock_sendmsg_nosec+0x18f/0x1d0 net/socket.c:737
 __sock_sendmsg net/socket.c:752 [inline]
 ____sys_sendmsg+0x577/0x880 net/socket.c:2610
 ___sys_sendmsg+0x21f/0x2a0 net/socket.c:2664
 __sys_sendmsg net/socket.c:2696 [inline]
 __do_sys_sendmsg net/socket.c:2701 [inline]
 __se_sys_sendmsg net/socket.c:2699 [inline]
 __x64_sys_sendmsg+0x19b/0x260 net/socket.c:2699
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f866d38f749
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:00007ffde2da5cd8 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007f866d5e5fa0 RCX: 00007f866d38f749
RDX: 0000000020000800 RSI: 0000200000000000 RDI: 0000000000000004
RBP: 00007f866d413f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f866d5e5fa0 R14: 00007f866d5e5fa0 R15: 0000000000000003
 </TASK>