====================================================== WARNING: possible circular locking dependency detected syzkaller #0 Not tainted ------------------------------------------------------ syz.0.1823/12436 is trying to acquire lock: ffffffff8e04f880 (fs_reclaim){+.+.}-{0:0}, at: might_alloc include/linux/sched/mm.h:317 [inline] ffffffff8e04f880 (fs_reclaim){+.+.}-{0:0}, at: prepare_alloc_pages+0x152/0x650 mm/page_alloc.c:4978 but task is already holding lock: ffffffff8e02df08 (pcpu_alloc_mutex){+.+.}-{4:4}, at: pcpu_alloc_noprof+0x25b/0x1750 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}: __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 net/socket.c:727 [inline] __sock_sendmsg+0x21c/0x270 net/socket.c:742 ____sys_sendmsg+0x505/0x820 net/socket.c:2592 ___sys_sendmsg+0x21f/0x2a0 net/socket.c:2646 __sys_sendmsg net/socket.c:2678 [inline] __do_sys_sendmsg net/socket.c:2683 [inline] __se_sys_sendmsg net/socket.c:2681 [inline] __x64_sys_sendmsg+0x19b/0x260 net/socket.c:2681 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 -> #1 (&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:1378 do_initcall_level+0x104/0x190 init/main.c:1440 do_initcalls+0x59/0xa0 init/main.c:1456 kernel_init_freeable+0x334/0x4b0 init/main.c:1688 kernel_init+0x1d/0x1d0 init/main.c:1578 ret_from_fork+0x599/0xb30 arch/x86/kernel/process.c:158 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246 -> #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 kernel/locking/lockdep.c:3908 [inline] __lock_acquire+0x15a6/0x2cf0 kernel/locking/lockdep.c:5237 lock_acquire+0x117/0x340 kernel/locking/lockdep.c:5868 __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 bpf_map_alloc_percpu+0xbc/0x1b0 kernel/bpf/syscall.c:575 prealloc_init+0x217/0x640 kernel/bpf/hashtab.c:332 htab_map_alloc+0x68c/0xc40 kernel/bpf/hashtab.c:557 map_create+0xafd/0x16a0 kernel/bpf/syscall.c:1514 __sys_bpf+0x5f0/0x860 kernel/bpf/syscall.c:6146 __do_sys_bpf kernel/bpf/syscall.c:6274 [inline] __se_sys_bpf kernel/bpf/syscall.c:6272 [inline] __x64_sys_bpf+0x7c/0x90 kernel/bpf/syscall.c:6272 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: 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.0.1823/12436: #0: ffffffff8e02df08 (pcpu_alloc_mutex){+.+.}-{4:4}, at: pcpu_alloc_noprof+0x25b/0x1750 mm/percpu.c:1782 stack backtrace: CPU: 1 UID: 0 PID: 12436 Comm: syz.0.1823 Not tainted syzkaller #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025 Call Trace: 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 __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 bpf_map_alloc_percpu+0xbc/0x1b0 kernel/bpf/syscall.c:575 prealloc_init+0x217/0x640 kernel/bpf/hashtab.c:332 htab_map_alloc+0x68c/0xc40 kernel/bpf/hashtab.c:557 map_create+0xafd/0x16a0 kernel/bpf/syscall.c:1514 __sys_bpf+0x5f0/0x860 kernel/bpf/syscall.c:6146 __do_sys_bpf kernel/bpf/syscall.c:6274 [inline] __se_sys_bpf kernel/bpf/syscall.c:6272 [inline] __x64_sys_bpf+0x7c/0x90 kernel/bpf/syscall.c:6272 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: 0033:0x7f8f3978f749 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:00007f8f3a59a038 EFLAGS: 00000246 ORIG_RAX: 0000000000000141 RAX: ffffffffffffffda RBX: 00007f8f399e5fa0 RCX: 00007f8f3978f749 RDX: 0000000000000048 RSI: 0000200000000840 RDI: 0000000000000000 RBP: 00007f8f39813f91 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 R13: 00007f8f399e6038 R14: 00007f8f399e5fa0 R15: 00007ffe741c8548