====================================================== WARNING: possible circular locking dependency detected 6.16.0-rc6-next-20250718-syzkaller #0 Not tainted ------------------------------------------------------ syz.5.1913/12143 is trying to acquire lock: ffffffff8e622c28 (pcpu_alloc_mutex){+.+.}-{4:4}, at: pcpu_alloc_noprof+0x286/0x16b0 mm/percpu.c:1782 but task is already holding lock: ffff888143b9c558 (&q->q_usage_counter(io)#55){++++}-{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)#55){++++}-{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:4400 [inline] __blk_mq_alloc_disk+0x15c/0x340 block/blk-mq.c:4447 nbd_dev_add+0x46c/0xae0 drivers/block/nbd.c:1943 nbd_init+0x21a/0x2d0 drivers/block/nbd.c:2680 do_one_initcall+0x233/0x820 init/main.c:1269 do_initcall_level+0x137/0x1f0 init/main.c:1331 do_initcalls+0x69/0xd0 init/main.c:1347 kernel_init_freeable+0x3d9/0x590 init/main.c:1579 kernel_init+0x1d/0x1d0 init/main.c:1469 ret_from_fork+0x3f9/0x770 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:4234 [inline] fs_reclaim_acquire+0x72/0x100 mm/page_alloc.c:4248 might_alloc include/linux/sched/mm.h:318 [inline] prepare_alloc_pages+0x153/0x610 mm/page_alloc.c:4916 __alloc_frozen_pages_noprof+0x123/0x370 mm/page_alloc.c:5137 __alloc_pages_noprof+0xa/0x30 mm/page_alloc.c:5182 __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+0x309/0x3e0 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+0x26b/0x290 net/netfilter/nf_sockopt.c:116 ip_getsockopt+0x1c4/0x220 net/ipv4/ip_sockglue.c:1777 do_sock_getsockopt+0x372/0x450 net/socket.c:2405 __sys_getsockopt net/socket.c:2434 [inline] __do_sys_getsockopt net/socket.c:2441 [inline] __se_sys_getsockopt net/socket.c:2438 [inline] __x64_sys_getsockopt+0x1a5/0x250 net/socket.c:2438 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+0x187/0x1360 kernel/locking/mutex.c:764 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:3542 [inline] blk_mq_alloc_map_and_rqs+0xbd/0x9f0 block/blk-mq.c:4098 __blk_mq_alloc_map_and_rqs block/blk-mq.c:4120 [inline] blk_mq_realloc_tag_set_tags block/blk-mq.c:4759 [inline] __blk_mq_update_nr_hw_queues block/blk-mq.c:4999 [inline] blk_mq_update_nr_hw_queues+0x76a/0x14c0 block/blk-mq.c:5047 nbd_start_device+0x17f/0xb10 drivers/block/nbd.c:1478 nbd_start_device_ioctl drivers/block/nbd.c:1537 [inline] __nbd_ioctl drivers/block/nbd.c:1612 [inline] nbd_ioctl+0x636/0xeb0 drivers/block/nbd.c:1652 blkdev_ioctl+0x5a5/0x6d0 block/ioctl.c:710 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:598 [inline] __se_sys_ioctl+0xf9/0x170 fs/ioctl.c:584 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)#55 Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&q->q_usage_counter(io)#55); lock(fs_reclaim); lock(&q->q_usage_counter(io)#55); lock(pcpu_alloc_mutex); *** DEADLOCK *** 4 locks held by syz.5.1913/12143: #0: ffff8880258d1988 (&set->update_nr_hwq_lock){++++}-{4:4}, at: blk_mq_update_nr_hw_queues+0x3b/0x14c0 block/blk-mq.c:5045 #1: ffff8880258d18d8 (&set->tag_list_lock){+.+.}-{4:4}, at: blk_mq_update_nr_hw_queues+0x49/0x14c0 block/blk-mq.c:5046 #2: ffff888143b9c558 (&q->q_usage_counter(io)#55){++++}-{0:0}, at: nbd_start_device+0x17f/0xb10 drivers/block/nbd.c:1478 #3: ffff888143b9c590 (&q->q_usage_counter(queue)#7){+.+.}-{0:0}, at: nbd_start_device+0x17f/0xb10 drivers/block/nbd.c:1478 stack backtrace: CPU: 1 UID: 0 PID: 12143 Comm: syz.5.1913 Not tainted 6.16.0-rc6-next-20250718-syzkaller #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025 Call Trace: 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+0x187/0x1360 kernel/locking/mutex.c:764 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:3542 [inline] blk_mq_alloc_map_and_rqs+0xbd/0x9f0 block/blk-mq.c:4098 __blk_mq_alloc_map_and_rqs block/blk-mq.c:4120 [inline] blk_mq_realloc_tag_set_tags block/blk-mq.c:4759 [inline] __blk_mq_update_nr_hw_queues block/blk-mq.c:4999 [inline] blk_mq_update_nr_hw_queues+0x76a/0x14c0 block/blk-mq.c:5047 nbd_start_device+0x17f/0xb10 drivers/block/nbd.c:1478 nbd_start_device_ioctl drivers/block/nbd.c:1537 [inline] __nbd_ioctl drivers/block/nbd.c:1612 [inline] nbd_ioctl+0x636/0xeb0 drivers/block/nbd.c:1652 blkdev_ioctl+0x5a5/0x6d0 block/ioctl.c:710 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:598 [inline] __se_sys_ioctl+0xf9/0x170 fs/ioctl.c:584 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: 0033:0x7f2d30b8e9a9 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:00007f2d3191c038 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 RAX: ffffffffffffffda RBX: 00007f2d30db5fa0 RCX: 00007f2d30b8e9a9 RDX: 0000000000000000 RSI: 000000000000ab03 RDI: 0000000000000004 RBP: 00007f2d30c10d69 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 R13: 0000000000000000 R14: 00007f2d30db5fa0 R15: 00007ffed6881468