======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz-executor/5929 is trying to acquire lock:
ffffffff8e045d20 (fs_reclaim){+.+.}-{0:0}, at: might_alloc include/linux/sched/mm.h:318 [inline]
ffffffff8e045d20 (fs_reclaim){+.+.}-{0:0}, at: prepare_alloc_pages+0x153/0x610 mm/page_alloc.c:4951

but task is already holding lock:
ffffffff8e025208 (pcpu_alloc_mutex){+.+.}-{4:4}, at: pcpu_alloc_noprof+0x286/0x1720 mm/percpu.c:1782

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (pcpu_alloc_mutex){+.+.}-{4:4}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
       __mutex_lock_common kernel/locking/mutex.c:598 [inline]
       __mutex_lock+0x187/0x1350 kernel/locking/mutex.c:760
       pcpu_alloc_noprof+0x286/0x1720 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:3534 [inline]
       blk_mq_alloc_map_and_rqs+0xbb/0x9c0 block/blk-mq.c:4097
       __blk_mq_alloc_map_and_rqs block/blk-mq.c:4119 [inline]
       blk_mq_realloc_tag_set_tags block/blk-mq.c:4758 [inline]
       __blk_mq_update_nr_hw_queues block/blk-mq.c:5081 [inline]
       blk_mq_update_nr_hw_queues+0xa26/0x1ab0 block/blk-mq.c:5133
       nbd_start_device+0x17f/0xb10 drivers/block/nbd.c:1486
       nbd_genl_connect+0x135b/0x18f0 drivers/block/nbd.c:2236
       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 net/socket.c:727 [inline]
       __sock_sendmsg+0x21c/0x270 net/socket.c:742
       ____sys_sendmsg+0x505/0x830 net/socket.c:2630
       ___sys_sendmsg+0x21f/0x2a0 net/socket.c:2684
       __sys_sendmsg net/socket.c:2716 [inline]
       __do_sys_sendmsg net/socket.c:2721 [inline]
       __se_sys_sendmsg net/socket.c:2719 [inline]
       __x64_sys_sendmsg+0x19b/0x260 net/socket.c:2719
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (&q->q_usage_counter(io)#49){++++}-{0:0}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
       blk_alloc_queue+0x538/0x620 block/blk-core.c:461
       blk_mq_alloc_queue block/blk-mq.c:4399 [inline]
       __blk_mq_alloc_disk+0x15c/0x340 block/blk-mq.c:4446
       nbd_dev_add+0x46c/0xae0 drivers/block/nbd.c:1951
       nbd_init+0x168/0x1f0 drivers/block/nbd.c:2688
       do_one_initcall+0x236/0x820 init/main.c:1283
       do_initcall_level+0x104/0x190 init/main.c:1345
       do_initcalls+0x59/0xa0 init/main.c:1361
       kernel_init_freeable+0x334/0x4b0 init/main.c:1593
       kernel_init+0x1d/0x1d0 init/main.c:1483
       ret_from_fork+0x4bc/0x870 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #0 (fs_reclaim){+.+.}-{0:0}:
       check_prev_add kernel/locking/lockdep.c:3165 [inline]
       check_prevs_add kernel/locking/lockdep.c:3284 [inline]
       validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3908
       __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5237
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
       __fs_reclaim_acquire mm/page_alloc.c:4269 [inline]
       fs_reclaim_acquire+0x72/0x100 mm/page_alloc.c:4283
       might_alloc include/linux/sched/mm.h:318 [inline]
       prepare_alloc_pages+0x153/0x610 mm/page_alloc.c:4951
       __alloc_frozen_pages_noprof+0x123/0x370 mm/page_alloc.c:5172
       __alloc_pages_noprof+0xa/0x30 mm/page_alloc.c:5217
       __alloc_pages_node_noprof include/linux/gfp.h:284 [inline]
       alloc_pages_node_noprof include/linux/gfp.h:311 [inline]
       pcpu_alloc_pages mm/percpu-vm.c:95 [inline]
       pcpu_populate_chunk+0x182/0xb30 mm/percpu-vm.c:285
       pcpu_alloc_noprof+0xcbf/0x1720 mm/percpu.c:1870
       xt_percpu_counter_alloc+0x161/0x220 net/netfilter/x_tables.c:1934
       find_check_entry net/ipv6/netfilter/ip6_tables.c:545 [inline]
       translate_table+0x1323/0x2040 net/ipv6/netfilter/ip6_tables.c:733
       do_replace net/ipv6/netfilter/ip6_tables.c:1154 [inline]
       do_ip6t_set_ctl+0x970/0xce0 net/ipv6/netfilter/ip6_tables.c:1644
       nf_setsockopt+0x26f/0x290 net/netfilter/nf_sockopt.c:101
       do_sock_setsockopt+0x17c/0x1b0 net/socket.c:2360
       __sys_setsockopt net/socket.c:2385 [inline]
       __do_sys_setsockopt net/socket.c:2391 [inline]
       __se_sys_setsockopt net/socket.c:2388 [inline]
       __x64_sys_setsockopt+0x13f/0x1b0 net/socket.c:2388
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0xfa0 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:
  fs_reclaim --> &q->q_usage_counter(io)#49 --> pcpu_alloc_mutex

 Possible unsafe locking scenario:

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

 *** DEADLOCK ***

1 lock held by syz-executor/5929:
 #0: ffffffff8e025208 (pcpu_alloc_mutex){+.+.}-{4:4}, at: pcpu_alloc_noprof+0x286/0x1720 mm/percpu.c:1782

stack backtrace:
CPU: 0 UID: 0 PID: 5929 Comm: syz-executor 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 lib/dump_stack.c:120
 print_circular_bug+0x2ee/0x310 kernel/locking/lockdep.c:2043
 check_noncircular+0x134/0x160 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+0xb9b/0x2140 kernel/locking/lockdep.c:3908
 __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5237
 lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
 __fs_reclaim_acquire mm/page_alloc.c:4269 [inline]
 fs_reclaim_acquire+0x72/0x100 mm/page_alloc.c:4283
 might_alloc include/linux/sched/mm.h:318 [inline]
 prepare_alloc_pages+0x153/0x610 mm/page_alloc.c:4951
 __alloc_frozen_pages_noprof+0x123/0x370 mm/page_alloc.c:5172
 __alloc_pages_noprof+0xa/0x30 mm/page_alloc.c:5217
 __alloc_pages_node_noprof include/linux/gfp.h:284 [inline]
 alloc_pages_node_noprof include/linux/gfp.h:311 [inline]
 pcpu_alloc_pages mm/percpu-vm.c:95 [inline]
 pcpu_populate_chunk+0x182/0xb30 mm/percpu-vm.c:285
 pcpu_alloc_noprof+0xcbf/0x1720 mm/percpu.c:1870
 xt_percpu_counter_alloc+0x161/0x220 net/netfilter/x_tables.c:1934
 find_check_entry net/ipv6/netfilter/ip6_tables.c:545 [inline]
 translate_table+0x1323/0x2040 net/ipv6/netfilter/ip6_tables.c:733
 do_replace net/ipv6/netfilter/ip6_tables.c:1154 [inline]
 do_ip6t_set_ctl+0x970/0xce0 net/ipv6/netfilter/ip6_tables.c:1644
 nf_setsockopt+0x26f/0x290 net/netfilter/nf_sockopt.c:101
 do_sock_setsockopt+0x17c/0x1b0 net/socket.c:2360
 __sys_setsockopt net/socket.c:2385 [inline]
 __do_sys_setsockopt net/socket.c:2391 [inline]
 __se_sys_setsockopt net/socket.c:2388 [inline]
 __x64_sys_setsockopt+0x13f/0x1b0 net/socket.c:2388
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f3ef9d90eba
Code: ff ff ff c3 0f 1f 40 00 48 c7 c2 a8 ff ff ff f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb b7 0f 1f 00 49 89 ca b8 36 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 06 c3 0f 1f 44 00 00 48 c7 c2 a8 ff ff ff f7
RSP: 002b:00007ffc06a37968 EFLAGS: 00000206 ORIG_RAX: 0000000000000036
RAX: ffffffffffffffda RBX: 00007ffc06a379f0 RCX: 00007f3ef9d90eba
RDX: 0000000000000040 RSI: 0000000000000029 RDI: 0000000000000003
RBP: 0000000000000003 R08: 00000000000003b8 R09: ffffffff00000000
R10: 00007f3ef9fb2d00 R11: 0000000000000206 R12: 00007f3ef9fb2ca0
R13: 00007ffc06a3798c R14: 0000000000000000 R15: 00007f3ef9fb4e60
 </TASK>
