====================================================== WARNING: possible circular locking dependency detected syzkaller #0 Not tainted ------------------------------------------------------ kworker/u8:1/13 is trying to acquire lock: ffffffff8fe8de00 (fs_reclaim){+.+.}-{0:0}, at: might_alloc include/linux/sched/mm.h:316 [inline] ffffffff8fe8de00 (fs_reclaim){+.+.}-{0:0}, at: slab_pre_alloc_hook mm/slub.c:4636 [inline] ffffffff8fe8de00 (fs_reclaim){+.+.}-{0:0}, at: slab_alloc_node mm/slub.c:4974 [inline] ffffffff8fe8de00 (fs_reclaim){+.+.}-{0:0}, at: __kmalloc_cache_noprof+0x61/0x600 mm/slub.c:5559 but task is already holding lock: ffffffff8fbf5d60 (wq_pool_mutex){+.+.}-{4:4}, at: __alloc_workqueue+0xe8d/0x21d0 kernel/workqueue.c:6201 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #8 (wq_pool_mutex){+.+.}-{4:4}: __mutex_lock_common kernel/locking/mutex.c:646 [inline] __mutex_lock+0x197/0x15a0 kernel/locking/mutex.c:821 __alloc_workqueue+0xe8d/0x21d0 kernel/workqueue.c:6201 alloc_workqueue_va kernel/workqueue.c:6253 [inline] alloc_workqueue_noprof+0xe3/0x210 kernel/workqueue.c:6269 padata_alloc+0xbe/0x360 kernel/padata.c:964 pcrypt_init_padata+0x27/0x100 crypto/pcrypt.c:335 pcrypt_init+0x60/0xc0 crypto/pcrypt.c:360 do_one_initcall+0x250/0x870 init/main.c:1362 do_initcall_level+0x10a/0x1a0 init/main.c:1424 do_initcalls+0x59/0xa0 init/main.c:1440 kernel_init_freeable+0x29d/0x3e0 init/main.c:1675 kernel_init+0x22/0x1d0 init/main.c:1565 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 -> #7 (cpu_hotplug_lock){++++}-{0:0}: percpu_down_read_internal include/linux/percpu-rwsem.h:53 [inline] percpu_down_read include/linux/percpu-rwsem.h:77 [inline] cpus_read_lock+0x3d/0x160 kernel/cpu.c:490 static_key_slow_inc+0x12/0x30 kernel/jump_label.c:190 udp_tunnel_encap_enable include/net/udp_tunnel.h:234 [inline] setup_udp_tunnel_sock+0x2eb/0x4f0 net/ipv4/udp_tunnel_core.c:90 l2tp_tunnel_register+0xe77/0x1570 net/l2tp/l2tp_core.c:1690 pppol2tp_tunnel_get net/l2tp/l2tp_ppp.c:663 [inline] pppol2tp_connect+0x8e3/0x18b0 net/l2tp/l2tp_ppp.c:711 connect_socket net/socket.c:2143 [inline] __sys_connect_file net/socket.c:2168 [inline] __sys_connect+0x316/0x450 net/socket.c:2185 __do_sys_connect net/socket.c:2191 [inline] __se_sys_connect net/socket.c:2188 [inline] __x64_sys_connect+0x7a/0x90 net/socket.c:2188 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline] do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84 entry_SYSCALL_64_after_hwframe+0x77/0x7f -> #6 (sk_lock-AF_INET){+.+.}-{0:0}: lock_sock_nested+0x41/0x100 net/core/sock.c:3908 lock_sock include/net/sock.h:1717 [inline] inet_shutdown+0x6a/0x390 net/ipv4/af_inet.c:910 nbd_mark_nsock_dead+0x2cb/0x550 drivers/block/nbd.c:319 recv_work+0x1cee/0x1e10 drivers/block/nbd.c:1030 process_one_work kernel/workqueue.c:3495 [inline] process_scheduled_works+0xc3d/0x1630 kernel/workqueue.c:3578 worker_thread+0xa47/0xfb0 kernel/workqueue.c:3659 kthread+0x38b/0x480 kernel/kthread.c:436 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 -> #5 (&nsock->tx_lock){+.+.}-{4:4}: __mutex_lock_common kernel/locking/mutex.c:646 [inline] __mutex_lock+0x197/0x15a0 kernel/locking/mutex.c:821 nbd_handle_cmd drivers/block/nbd.c:1143 [inline] nbd_queue_rq+0x373/0xff0 drivers/block/nbd.c:1207 blk_mq_dispatch_rq_list+0x499/0x1990 block/blk-mq.c:2130 __blk_mq_do_dispatch_sched block/blk-mq-sched.c:168 [inline] blk_mq_do_dispatch_sched block/blk-mq-sched.c:182 [inline] __blk_mq_sched_dispatch_requests+0xd36/0x1580 block/blk-mq-sched.c:307 blk_mq_sched_dispatch_requests+0xd7/0x190 block/blk-mq-sched.c:329 blk_mq_run_work_fn+0x167/0x2f0 block/blk-mq.c:2545 process_one_work kernel/workqueue.c:3495 [inline] process_scheduled_works+0xc3d/0x1630 kernel/workqueue.c:3578 worker_thread+0xa47/0xfb0 kernel/workqueue.c:3659 kthread+0x38b/0x480 kernel/kthread.c:436 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 -> #4 (&cmd->lock){+.+.}-{4:4}: __mutex_lock_common kernel/locking/mutex.c:646 [inline] __mutex_lock+0x197/0x15a0 kernel/locking/mutex.c:821 nbd_queue_rq+0xc1/0xff0 drivers/block/nbd.c:1199 blk_mq_dispatch_rq_list+0x499/0x1990 block/blk-mq.c:2130 __blk_mq_do_dispatch_sched block/blk-mq-sched.c:168 [inline] blk_mq_do_dispatch_sched block/blk-mq-sched.c:182 [inline] __blk_mq_sched_dispatch_requests+0xd36/0x1580 block/blk-mq-sched.c:307 blk_mq_sched_dispatch_requests+0xd7/0x190 block/blk-mq-sched.c:329 blk_mq_run_work_fn+0x167/0x2f0 block/blk-mq.c:2545 process_one_work kernel/workqueue.c:3495 [inline] process_scheduled_works+0xc3d/0x1630 kernel/workqueue.c:3578 worker_thread+0xa47/0xfb0 kernel/workqueue.c:3659 kthread+0x38b/0x480 kernel/kthread.c:436 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 -> #3 (set->srcu){.+.+}-{0:0}: srcu_lock_sync include/linux/srcu.h:225 [inline] __synchronize_srcu+0xca/0x2f0 kernel/rcu/srcutree.c:1662 elevator_switch+0x1e8/0x7b0 block/elevator.c:576 elevator_change+0x2fa/0x480 block/elevator.c:681 elevator_set_default+0x375/0x440 block/elevator.c:754 blk_register_queue+0x404/0x4f0 block/blk-sysfs.c:992 __add_disk+0x6b8/0xdb0 block/genhd.c:531 add_disk_fwnode+0x100/0x3a0 block/genhd.c:600 add_disk include/linux/blkdev.h:798 [inline] nbd_dev_add+0x733/0xb60 drivers/block/nbd.c:2026 nbd_init+0x168/0x1f0 drivers/block/nbd.c:2743 do_one_initcall+0x250/0x870 init/main.c:1362 do_initcall_level+0x10a/0x1a0 init/main.c:1424 do_initcalls+0x59/0xa0 init/main.c:1440 kernel_init_freeable+0x29d/0x3e0 init/main.c:1675 kernel_init+0x22/0x1d0 init/main.c:1565 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 -> #2 (&q->elevator_lock){+.+.}-{4:4}: __mutex_lock_common kernel/locking/mutex.c:646 [inline] __mutex_lock+0x197/0x15a0 kernel/locking/mutex.c:821 elevator_change+0x1af/0x480 block/elevator.c:679 elevator_set_none+0xb5/0x140 block/elevator.c:769 blk_mq_elv_switch_none block/blk-mq.c:5113 [inline] __blk_mq_update_nr_hw_queues block/blk-mq.c:5158 [inline] blk_mq_update_nr_hw_queues+0x5ef/0x19f0 block/blk-mq.c:5223 nbd_start_device+0x189/0xb30 drivers/block/nbd.c:1530 nbd_genl_connect+0x167d/0x1cd0 drivers/block/nbd.c:2310 genl_family_rcv_msg_doit+0x233/0x340 net/netlink/genetlink.c:1114 genl_family_rcv_msg net/netlink/genetlink.c:1194 [inline] genl_rcv_msg+0x614/0x7a0 net/netlink/genetlink.c:1209 netlink_rcv_skb+0x226/0x4a0 net/netlink/af_netlink.c:2580 genl_rcv+0x28/0x40 net/netlink/genetlink.c:1218 netlink_unicast_kernel net/netlink/af_netlink.c:1335 [inline] netlink_unicast+0x8ef/0xa80 net/netlink/af_netlink.c:1361 netlink_sendmsg+0x7f0/0xb20 net/netlink/af_netlink.c:1920 sock_sendmsg_nosec+0x14e/0x190 net/socket.c:800 __sock_sendmsg net/socket.c:818 [inline] ____sys_sendmsg+0x54e/0x850 net/socket.c:2715 ___sys_sendmsg+0x2a5/0x360 net/socket.c:2769 __sys_sendmsg net/socket.c:2801 [inline] __do_sys_sendmsg net/socket.c:2806 [inline] __se_sys_sendmsg net/socket.c:2804 [inline] __x64_sys_sendmsg+0x1b1/0x290 net/socket.c:2804 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline] do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84 entry_SYSCALL_64_after_hwframe+0x77/0x7f -> #1 (&q->q_usage_counter(io)#49){++++}-{0:0}: blk_alloc_queue+0x544/0x690 block/blk-core.c:504 blk_mq_alloc_queue block/blk-mq.c:4431 [inline] __blk_mq_alloc_disk+0x194/0x390 block/blk-mq.c:4478 nbd_dev_add+0x494/0xb60 drivers/block/nbd.c:1996 nbd_init+0x168/0x1f0 drivers/block/nbd.c:2743 do_one_initcall+0x250/0x870 init/main.c:1362 do_initcall_level+0x10a/0x1a0 init/main.c:1424 do_initcalls+0x59/0xa0 init/main.c:1440 kernel_init_freeable+0x29d/0x3e0 init/main.c:1675 kernel_init+0x22/0x1d0 init/main.c:1565 ret_from_fork+0x514/0xb70 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:3209 [inline] check_prevs_add kernel/locking/lockdep.c:3328 [inline] validate_chain kernel/locking/lockdep.c:3952 [inline] __lock_acquire+0x164c/0x2de0 kernel/locking/lockdep.c:5288 lock_acquire+0x115/0x350 kernel/locking/lockdep.c:5942 __fs_reclaim_acquire mm/page_alloc.c:4375 [inline] fs_reclaim_acquire+0x71/0x100 mm/page_alloc.c:4389 might_alloc include/linux/sched/mm.h:316 [inline] slab_pre_alloc_hook mm/slub.c:4636 [inline] slab_alloc_node mm/slub.c:4974 [inline] __kmalloc_cache_noprof+0x61/0x600 mm/slub.c:5559 _kmalloc_noprof include/linux/slab.h:991 [inline] _kzalloc_noprof include/linux/slab.h:1312 [inline] alloc_workqueue_attrs_noprof kernel/workqueue.c:4999 [inline] alloc_wq_std_attrs kernel/workqueue.c:5927 [inline] alloc_and_link_pwqs kernel/workqueue.c:5951 [inline] __alloc_workqueue+0xf5f/0x21d0 kernel/workqueue.c:6203 alloc_workqueue_va kernel/workqueue.c:6253 [inline] alloc_workqueue_noprof+0xe3/0x210 kernel/workqueue.c:6269 __rds_conn_create+0x1334/0x2290 net/rds/connection.c:291 rds_conn_create+0x43/0x60 net/rds/connection.c:384 rds_tcp_accept_one+0x44f/0xd40 net/rds/tcp_listen.c:226 rds_tcp_accept_worker+0x1d/0x70 net/rds/tcp.c:603 process_one_work kernel/workqueue.c:3495 [inline] process_scheduled_works+0xc3d/0x1630 kernel/workqueue.c:3578 worker_thread+0xa47/0xfb0 kernel/workqueue.c:3659 kthread+0x38b/0x480 kernel/kthread.c:436 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 other info that might help us debug this: Chain exists of: fs_reclaim --> cpu_hotplug_lock --> wq_pool_mutex Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(wq_pool_mutex); lock(cpu_hotplug_lock); lock(wq_pool_mutex); lock(fs_reclaim); *** DEADLOCK *** locks held by kworker/u8:1/13: 4, last CPU#1: #0: ffff8880340bd148 ((wq_completion)krdsd){+.+.}-{0:0}, at: rcu_lock_acquire include/linux/rcupdate.h:309 [inline] #0: ffff8880340bd148 ((wq_completion)krdsd){+.+.}-{0:0}, at: rcu_read_lock include/linux/rcupdate.h:849 [inline] #0: ffff8880340bd148 ((wq_completion)krdsd){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3460 [inline] #0: ffff8880340bd148 ((wq_completion)krdsd){+.+.}-{0:0}, at: process_scheduled_works+0x97a/0x1630 kernel/workqueue.c:3578 #1: ffffc90000127c40 ((work_completion)(&rtn->rds_tcp_accept_w)){+.+.}-{0:0}, at: rcu_lock_acquire include/linux/rcupdate.h:309 [inline] #1: ffffc90000127c40 ((work_completion)(&rtn->rds_tcp_accept_w)){+.+.}-{0:0}, at: rcu_read_lock include/linux/rcupdate.h:849 [inline] #1: ffffc90000127c40 ((work_completion)(&rtn->rds_tcp_accept_w)){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3460 [inline] #1: ffffc90000127c40 ((work_completion)(&rtn->rds_tcp_accept_w)){+.+.}-{0:0}, at: process_scheduled_works+0x97a/0x1630 kernel/workqueue.c:3578 #2: ffff888042fe9060 (&rtn->rds_tcp_accept_lock){+.+.}-{4:4}, at: rds_tcp_accept_one+0xb3/0xd40 net/rds/tcp_listen.c:172 #3: ffffffff8fbf5d60 (wq_pool_mutex){+.+.}-{4:4}, at: __alloc_workqueue+0xe8d/0x21d0 kernel/workqueue.c:6201 stack backtrace: CPU: 1 UID: 0 PID: 13 Comm: kworker/u8:1 Not tainted syzkaller #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/07/2026 Workqueue: krdsd rds_tcp_accept_worker Call Trace: dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120 print_circular_bug+0x2e2/0x300 kernel/locking/lockdep.c:2087 check_noncircular+0x12f/0x150 kernel/locking/lockdep.c:2219 check_prev_add kernel/locking/lockdep.c:3209 [inline] check_prevs_add kernel/locking/lockdep.c:3328 [inline] validate_chain kernel/locking/lockdep.c:3952 [inline] __lock_acquire+0x164c/0x2de0 kernel/locking/lockdep.c:5288 lock_acquire+0x115/0x350 kernel/locking/lockdep.c:5942 __fs_reclaim_acquire mm/page_alloc.c:4375 [inline] fs_reclaim_acquire+0x71/0x100 mm/page_alloc.c:4389 might_alloc include/linux/sched/mm.h:316 [inline] slab_pre_alloc_hook mm/slub.c:4636 [inline] slab_alloc_node mm/slub.c:4974 [inline] __kmalloc_cache_noprof+0x61/0x600 mm/slub.c:5559 _kmalloc_noprof include/linux/slab.h:991 [inline] _kzalloc_noprof include/linux/slab.h:1312 [inline] alloc_workqueue_attrs_noprof kernel/workqueue.c:4999 [inline] alloc_wq_std_attrs kernel/workqueue.c:5927 [inline] alloc_and_link_pwqs kernel/workqueue.c:5951 [inline] __alloc_workqueue+0xf5f/0x21d0 kernel/workqueue.c:6203 alloc_workqueue_va kernel/workqueue.c:6253 [inline] alloc_workqueue_noprof+0xe3/0x210 kernel/workqueue.c:6269 __rds_conn_create+0x1334/0x2290 net/rds/connection.c:291 rds_conn_create+0x43/0x60 net/rds/connection.c:384 rds_tcp_accept_one+0x44f/0xd40 net/rds/tcp_listen.c:226 rds_tcp_accept_worker+0x1d/0x70 net/rds/tcp.c:603 process_one_work kernel/workqueue.c:3495 [inline] process_scheduled_works+0xc3d/0x1630 kernel/workqueue.c:3578 worker_thread+0xa47/0xfb0 kernel/workqueue.c:3659 kthread+0x38b/0x480 kernel/kthread.c:436 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245