======================================================
WARNING: possible circular locking dependency detected
6.16.0-rc4-syzkaller-g1f988d0788f5 #0 Not tainted
------------------------------------------------------
syz-executor.0/6196 is trying to acquire lock:
ffffffff8e225768 (pcpu_alloc_mutex){+.+.}-{4:4}, at: pcpu_alloc_noprof+0x286/0x16b0 mm/percpu.c:1782

but task is already holding lock:
ffff888142b10a70 (&q->q_usage_counter(io)#49){++++}-{0:0}, at: nbd_start_device+0x16c/0xac0 drivers/block/nbd.c:1476

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:5871
       blk_alloc_queue+0x538/0x620 block/blk-core.c:461
       blk_mq_alloc_queue block/blk-mq.c:4396 [inline]
       __blk_mq_alloc_disk+0x162/0x340 block/blk-mq.c:4443
       nbd_dev_add+0x476/0xb00 drivers/block/nbd.c:1933
       nbd_init+0x21a/0x2d0 drivers/block/nbd.c:2670
       do_one_initcall+0x236/0x820 init/main.c:1274
       do_initcall_level+0x137/0x1f0 init/main.c:1336
       do_initcalls+0x69/0xd0 init/main.c:1352
       kernel_init_freeable+0x3d9/0x570 init/main.c:1584
       kernel_init+0x1d/0x1d0 init/main.c:1474
       ret_from_fork+0x3fc/0x770 arch/x86/kernel/process.c:148
       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:5871
       __fs_reclaim_acquire mm/page_alloc.c:4045 [inline]
       fs_reclaim_acquire+0x72/0x100 mm/page_alloc.c:4059
       might_alloc include/linux/sched/mm.h:318 [inline]
       prepare_alloc_pages+0x153/0x610 mm/page_alloc.c:4727
       __alloc_frozen_pages_noprof+0x123/0x370 mm/page_alloc.c:4948
       __alloc_pages_noprof+0xa/0x30 mm/page_alloc.c:4993
       __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/0x16b0 mm/percpu.c:1870
       xt_percpu_counter_alloc+0x161/0x220 net/netfilter/x_tables.c:1931
       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_nat_table_init+0x43/0x2e0 net/ipv4/netfilter/iptable_nat.c:115
       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+0x360/0x650 net/socket.c:2357
       __sys_getsockopt net/socket.c:2386 [inline]
       __do_sys_getsockopt net/socket.c:2393 [inline]
       __se_sys_getsockopt net/socket.c:2390 [inline]
       __x64_sys_getsockopt+0x1a5/0x250 net/socket.c:2390
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0x3b0 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:3168 [inline]
       check_prevs_add kernel/locking/lockdep.c:3287 [inline]
       validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3911
       __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5240
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5871
       __mutex_lock_common kernel/locking/mutex.c:602 [inline]
       __mutex_lock+0x182/0xe80 kernel/locking/mutex.c:747
       pcpu_alloc_noprof+0x286/0x16b0 mm/percpu.c:1782
       init_alloc_hint lib/sbitmap.c:16 [inline]
       sbitmap_init_node+0x1e1/0x630 lib/sbitmap.c:126
       sbitmap_queue_init_node+0x41/0x660 lib/sbitmap.c:438
       bt_alloc block/blk-mq-tag.c:542 [inline]
       blk_mq_init_tags+0x110/0x280 block/blk-mq-tag.c:565
       blk_mq_alloc_rq_map block/blk-mq.c:3538 [inline]
       blk_mq_alloc_map_and_rqs+0xbd/0x9f0 block/blk-mq.c:4094
       __blk_mq_alloc_map_and_rqs block/blk-mq.c:4116 [inline]
       blk_mq_realloc_tag_set_tags block/blk-mq.c:4755 [inline]
       __blk_mq_update_nr_hw_queues block/blk-mq.c:4995 [inline]
       blk_mq_update_nr_hw_queues+0x76a/0x14c0 block/blk-mq.c:5043
       nbd_start_device+0x16c/0xac0 drivers/block/nbd.c:1476
       nbd_start_device_ioctl drivers/block/nbd.c:1527 [inline]
       __nbd_ioctl drivers/block/nbd.c:1602 [inline]
       nbd_ioctl+0x636/0xeb0 drivers/block/nbd.c:1642
       blkdev_ioctl+0x5a8/0x6d0 block/ioctl.c:704
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:907 [inline]
       __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:893
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0x3b0 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 ***

5 locks held by syz-executor.0/6196:
 #0: ffff8880251a0a30 (&nbd->config_lock){+.+.}-{4:4}, at: nbd_ioctl+0x131/0xeb0 drivers/block/nbd.c:1635
 #1: ffff8880251a0988 (&set->update_nr_hwq_lock){++++}-{4:4}, at: blk_mq_update_nr_hw_queues+0x3b/0x14c0 block/blk-mq.c:5041
 #2: ffff8880251a08d8 (&set->tag_list_lock){+.+.}-{4:4}, at: blk_mq_update_nr_hw_queues+0x49/0x14c0 block/blk-mq.c:5042
 #3: ffff888142b10a70 (&q->q_usage_counter(io)#49){++++}-{0:0}, at: nbd_start_device+0x16c/0xac0 drivers/block/nbd.c:1476
 #4: ffff888142b10aa8 (&q->q_usage_counter(queue)){+.+.}-{0:0}, at: nbd_start_device+0x16c/0xac0 drivers/block/nbd.c:1476

stack backtrace:
CPU: 1 UID: 0 PID: 6196 Comm: syz-executor.0 Not tainted 6.16.0-rc4-syzkaller-g1f988d0788f5 #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 print_circular_bug+0x2ee/0x310 kernel/locking/lockdep.c:2046
 check_noncircular+0x134/0x160 kernel/locking/lockdep.c:2178
 check_prev_add kernel/locking/lockdep.c:3168 [inline]
 check_prevs_add kernel/locking/lockdep.c:3287 [inline]
 validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3911
 __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5240
 lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5871
 __mutex_lock_common kernel/locking/mutex.c:602 [inline]
 __mutex_lock+0x182/0xe80 kernel/locking/mutex.c:747
 pcpu_alloc_noprof+0x286/0x16b0 mm/percpu.c:1782
 init_alloc_hint lib/sbitmap.c:16 [inline]
 sbitmap_init_node+0x1e1/0x630 lib/sbitmap.c:126
 sbitmap_queue_init_node+0x41/0x660 lib/sbitmap.c:438
 bt_alloc block/blk-mq-tag.c:542 [inline]
 blk_mq_init_tags+0x110/0x280 block/blk-mq-tag.c:565
 blk_mq_alloc_rq_map block/blk-mq.c:3538 [inline]
 blk_mq_alloc_map_and_rqs+0xbd/0x9f0 block/blk-mq.c:4094
 __blk_mq_alloc_map_and_rqs block/blk-mq.c:4116 [inline]
 blk_mq_realloc_tag_set_tags block/blk-mq.c:4755 [inline]
 __blk_mq_update_nr_hw_queues block/blk-mq.c:4995 [inline]
 blk_mq_update_nr_hw_queues+0x76a/0x14c0 block/blk-mq.c:5043
 nbd_start_device+0x16c/0xac0 drivers/block/nbd.c:1476
 nbd_start_device_ioctl drivers/block/nbd.c:1527 [inline]
 __nbd_ioctl drivers/block/nbd.c:1602 [inline]
 nbd_ioctl+0x636/0xeb0 drivers/block/nbd.c:1642
 blkdev_ioctl+0x5a8/0x6d0 block/ioctl.c:704
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:907 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:893
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f5ccc8799e9
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 b0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f5ccda960c8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f5ccc98bf60 RCX: 00007f5ccc8799e9
RDX: 0000000000000000 RSI: 000000000000ab03 RDI: 0000000000000007
RBP: 00007f5ccda96120 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000002
R13: 000000000000000b R14: 00007f5ccc98bf60 R15: 00007ffe3f316b18
 </TASK>
FAULT_INJECTION: forcing a failure.
name failslab, interval 1, probability 0, space 0, times 1
CPU: 0 UID: 0 PID: 6196 Comm: syz-executor.0 Not tainted 6.16.0-rc4-syzkaller-g1f988d0788f5 #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 fail_dump lib/fault-inject.c:73 [inline]
 should_fail_ex+0x414/0x560 lib/fault-inject.c:174
 should_failslab+0xa8/0x100 mm/failslab.c:46
 slab_pre_alloc_hook mm/slub.c:4101 [inline]
 slab_alloc_node mm/slub.c:4177 [inline]
 __do_kmalloc_node mm/slub.c:4327 [inline]
 __kmalloc_noprof+0xcb/0x4f0 mm/slub.c:4340
 kmalloc_noprof include/linux/slab.h:909 [inline]
 kmalloc_array_noprof include/linux/slab.h:948 [inline]
 alloc_node_to_cpumask lib/group_cpus.c:50 [inline]
 group_cpus_evenly+0xc0/0x530 lib/group_cpus.c:364
 blk_mq_map_queues+0x4c/0x400 block/blk-mq-cpumap.c:24
 __blk_mq_update_nr_hw_queues block/blk-mq.c:5002 [inline]
 blk_mq_update_nr_hw_queues+0x91c/0x14c0 block/blk-mq.c:5043
 nbd_start_device+0x16c/0xac0 drivers/block/nbd.c:1476
 nbd_start_device_ioctl drivers/block/nbd.c:1527 [inline]
 __nbd_ioctl drivers/block/nbd.c:1602 [inline]
 nbd_ioctl+0x636/0xeb0 drivers/block/nbd.c:1642
 blkdev_ioctl+0x5a8/0x6d0 block/ioctl.c:704
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:907 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:893
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f5ccc8799e9
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 b0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f5ccda960c8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f5ccc98bf60 RCX: 00007f5ccc8799e9
RDX: 0000000000000000 RSI: 000000000000ab03 RDI: 0000000000000007
RBP: 00007f5ccda96120 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000002
R13: 000000000000000b R14: 00007f5ccc98bf60 R15: 00007ffe3f316b18
 </TASK>
block nbd0: shutting down sockets