======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.3.2736/12613 is trying to acquire lock:
ffffffff8e621488 (pcpu_alloc_mutex){+.+.}-{4:4}, at: pcpu_alloc_noprof+0x286/0x1720 mm/percpu.c:1782

but task is already holding lock:
ffff88802537e2c8 (&q->q_usage_counter(io)#49){++++}-{0:0}, at: nbd_start_device+0x17f/0xb10 drivers/block/nbd.c:1478

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}:
       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:4391 [inline]
       __blk_mq_alloc_disk+0x15c/0x340 block/blk-mq.c:4438
       nbd_dev_add+0x46c/0xae0 drivers/block/nbd.c:1943
       nbd_init+0x168/0x1f0 drivers/block/nbd.c:2680
       do_one_initcall+0x233/0x820 init/main.c:1281
       do_initcall_level+0x104/0x190 init/main.c:1343
       do_initcalls+0x59/0xa0 init/main.c:1359
       kernel_init_freeable+0x334/0x4b0 init/main.c:1591
       kernel_init+0x1d/0x1d0 init/main.c:1481
       ret_from_fork+0x47c/0x820 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #1 (fs_reclaim){+.+.}-{0:0}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
       __fs_reclaim_acquire mm/page_alloc.c:4239 [inline]
       fs_reclaim_acquire+0x72/0x100 mm/page_alloc.c:4253
       might_alloc include/linux/sched/mm.h:318 [inline]
       prepare_alloc_pages+0x153/0x610 mm/page_alloc.c:4921
       __alloc_frozen_pages_noprof+0x123/0x370 mm/page_alloc.c:5142
       __alloc_pages_noprof+0xa/0x30 mm/page_alloc.c:5187
       __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
       gro_cells_init+0x3e/0x220 net/core/gro_cells.c:74
       ip6gre_tunnel_init_common+0xec/0x980 net/ipv6/ip6_gre.c:1478
       ip6gre_tunnel_init+0x1d/0x150 net/ipv6/ip6_gre.c:1508
       register_netdevice+0x6bf/0x1ae0 net/core/dev.c:11182
       register_netdev+0x40/0x60 net/core/dev.c:11371
       ip6gre_init_net+0x291/0x3c0 net/ipv6/ip6_gre.c:1599
       ops_init+0x35c/0x5c0 net/core/net_namespace.c:136
       setup_net+0x10c/0x320 net/core/net_namespace.c:438
       copy_net_ns+0x31b/0x4d0 net/core/net_namespace.c:570
       create_new_namespaces+0x3f3/0x720 kernel/nsproxy.c:110
       copy_namespaces+0x438/0x4b0 kernel/nsproxy.c:175
       copy_process+0x1733/0x3c00 kernel/fork.c:2195
       kernel_clone+0x21e/0x840 kernel/fork.c:2620
       __do_sys_clone kernel/fork.c:2761 [inline]
       __se_sys_clone kernel/fork.c:2745 [inline]
       __x64_sys_clone+0x18b/0x1e0 kernel/fork.c:2745
       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

-> #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+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
       __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:549 [inline]
       blk_mq_init_tags+0x110/0x280 block/blk-mq-tag.c:572
       blk_mq_alloc_rq_map block/blk-mq.c:3524 [inline]
       blk_mq_alloc_map_and_rqs+0xc2/0xa00 block/blk-mq.c:4089
       __blk_mq_alloc_map_and_rqs block/blk-mq.c:4111 [inline]
       blk_mq_realloc_tag_set_tags block/blk-mq.c:4750 [inline]
       __blk_mq_update_nr_hw_queues block/blk-mq.c:5072 [inline]
       blk_mq_update_nr_hw_queues+0xa26/0x1ab0 block/blk-mq.c:5124
       nbd_start_device+0x17f/0xb10 drivers/block/nbd.c:1478
       nbd_genl_connect+0x135b/0x18f0 drivers/block/nbd.c:2228
       genl_family_rcv_msg_doit+0x212/0x300 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+0x205/0x470 net/netlink/af_netlink.c:2552
       genl_rcv+0x28/0x40 net/netlink/genetlink.c:1219
       netlink_unicast_kernel net/netlink/af_netlink.c:1320 [inline]
       netlink_unicast+0x82c/0x9e0 net/netlink/af_netlink.c:1346
       netlink_sendmsg+0x805/0xb30 net/netlink/af_netlink.c:1896
       sock_sendmsg_nosec net/socket.c:714 [inline]
       __sock_sendmsg+0x21c/0x270 net/socket.c:729
       ____sys_sendmsg+0x505/0x830 net/socket.c:2614
       ___sys_sendmsg+0x21f/0x2a0 net/socket.c:2668
       __sys_sendmsg net/socket.c:2700 [inline]
       __do_sys_sendmsg net/socket.c:2705 [inline]
       __se_sys_sendmsg net/socket.c:2703 [inline]
       __x64_sys_sendmsg+0x19b/0x260 net/socket.c:2703
       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:
  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.3.2736/12613:
 #0: ffffffff8f9b7290 (cb_lock){++++}-{4:4}, at: genl_rcv+0x19/0x40 net/netlink/genetlink.c:1218
 #1: ffffffff8f9b70a8 (genl_mutex){+.+.}-{4:4}, at: genl_lock net/netlink/genetlink.c:35 [inline]
 #1: ffffffff8f9b70a8 (genl_mutex){+.+.}-{4:4}, at: genl_op_lock net/netlink/genetlink.c:60 [inline]
 #1: ffffffff8f9b70a8 (genl_mutex){+.+.}-{4:4}, at: genl_rcv_msg+0x10d/0x790 net/netlink/genetlink.c:1209
 #2: ffff888143ba09c8 (&set->update_nr_hwq_lock){++++}-{4:4}, at: blk_mq_update_nr_hw_queues+0xa7/0x1ab0 block/blk-mq.c:5122
 #3: ffff888143ba08d8 (&set->tag_list_lock){+.+.}-{4:4}, at: blk_mq_update_nr_hw_queues+0xba/0x1ab0 block/blk-mq.c:5123
 #4: ffff88802537e2c8 (&q->q_usage_counter(io)#49){++++}-{0:0}, at: nbd_start_device+0x17f/0xb10 drivers/block/nbd.c:1478
 #5: ffff88802537e300 (&q->q_usage_counter(queue)#33){+.+.}-{0:0}, at: nbd_start_device+0x17f/0xb10 drivers/block/nbd.c:1478

stack backtrace:
CPU: 0 UID: 0 PID: 12613 Comm: syz.3.2736 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
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
 __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:549 [inline]
 blk_mq_init_tags+0x110/0x280 block/blk-mq-tag.c:572
 blk_mq_alloc_rq_map block/blk-mq.c:3524 [inline]
 blk_mq_alloc_map_and_rqs+0xc2/0xa00 block/blk-mq.c:4089
 __blk_mq_alloc_map_and_rqs block/blk-mq.c:4111 [inline]
 blk_mq_realloc_tag_set_tags block/blk-mq.c:4750 [inline]
 __blk_mq_update_nr_hw_queues block/blk-mq.c:5072 [inline]
 blk_mq_update_nr_hw_queues+0xa26/0x1ab0 block/blk-mq.c:5124
 nbd_start_device+0x17f/0xb10 drivers/block/nbd.c:1478
 nbd_genl_connect+0x135b/0x18f0 drivers/block/nbd.c:2228
 genl_family_rcv_msg_doit+0x212/0x300 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+0x205/0x470 net/netlink/af_netlink.c:2552
 genl_rcv+0x28/0x40 net/netlink/genetlink.c:1219
 netlink_unicast_kernel net/netlink/af_netlink.c:1320 [inline]
 netlink_unicast+0x82c/0x9e0 net/netlink/af_netlink.c:1346
 netlink_sendmsg+0x805/0xb30 net/netlink/af_netlink.c:1896
 sock_sendmsg_nosec net/socket.c:714 [inline]
 __sock_sendmsg+0x21c/0x270 net/socket.c:729
 ____sys_sendmsg+0x505/0x830 net/socket.c:2614
 ___sys_sendmsg+0x21f/0x2a0 net/socket.c:2668
 __sys_sendmsg net/socket.c:2700 [inline]
 __do_sys_sendmsg net/socket.c:2705 [inline]
 __se_sys_sendmsg net/socket.c:2703 [inline]
 __x64_sys_sendmsg+0x19b/0x260 net/socket.c:2703
 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: 0033:0x7f109fb8eba9
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:00007f10a0acc038 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007f109fdd5fa0 RCX: 00007f109fb8eba9
RDX: 0000000020000000 RSI: 0000200000001ac0 RDI: 0000000000000004
RBP: 00007f109fc11e19 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f109fdd6038 R14: 00007f109fdd5fa0 R15: 00007ffe4300cb08
 </TASK>
nbd0: detected capacity change from 0 to 127