====================================================== WARNING: possible circular locking dependency detected syzkaller #0 Not tainted ------------------------------------------------------ kworker/0:6/5961 is trying to acquire lock: ffffffff8e643960 (fs_reclaim){+.+.}-{0:0}, at: might_alloc include/linux/sched/mm.h:318 [inline] ffffffff8e643960 (fs_reclaim){+.+.}-{0:0}, at: slab_pre_alloc_hook mm/slub.c:4721 [inline] ffffffff8e643960 (fs_reclaim){+.+.}-{0:0}, at: slab_alloc_node mm/slub.c:5044 [inline] ffffffff8e643960 (fs_reclaim){+.+.}-{0:0}, at: kmem_cache_alloc_lru_noprof+0x4a/0x6d0 mm/slub.c:5087 but task is already holding lock: ffff88806f30ca60 (sk_lock-AF_INET){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1676 [inline] ffff88806f30ca60 (sk_lock-AF_INET){+.+.}-{0:0}, at: mptcp_worker+0x36/0x1160 net/mptcp/protocol.c:2739 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #6 (sk_lock-AF_INET){+.+.}-{0:0}: lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868 lock_sock_nested+0x48/0x100 net/core/sock.c:3720 lock_sock include/net/sock.h:1676 [inline] tcp_sendmsg+0x21/0x50 net/ipv4/tcp.c:1392 sock_sendmsg_nosec net/socket.c:714 [inline] __sock_sendmsg+0x19c/0x270 net/socket.c:729 sock_sendmsg+0x158/0x230 net/socket.c:752 __sock_xmit+0x1c1/0x470 drivers/block/nbd.c:574 sock_xmit drivers/block/nbd.c:602 [inline] nbd_send_cmd+0x863/0x1ba0 drivers/block/nbd.c:712 nbd_handle_cmd drivers/block/nbd.c:1174 [inline] nbd_queue_rq+0xcdb/0xf10 drivers/block/nbd.c:1204 blk_mq_dispatch_rq_list+0x4c0/0x1900 block/blk-mq.c:2129 __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+0xda4/0x1570 block/blk-mq-sched.c:307 blk_mq_sched_dispatch_requests+0xd7/0x190 block/blk-mq-sched.c:329 blk_mq_run_hw_queue+0x348/0x4f0 block/blk-mq.c:2367 blk_mq_dispatch_list+0xd0c/0xe00 include/linux/spinlock.h:-1 blk_mq_flush_plug_list+0x469/0x550 block/blk-mq.c:2976 __blk_flush_plug+0x3d3/0x4b0 block/blk-core.c:1223 blk_finish_plug block/blk-core.c:1250 [inline] __submit_bio+0x2d3/0x5a0 block/blk-core.c:649 __submit_bio_noacct_mq block/blk-core.c:722 [inline] submit_bio_noacct_nocheck+0x2fb/0xa50 block/blk-core.c:753 submit_bh fs/buffer.c:2829 [inline] __bread_slow fs/buffer.c:1272 [inline] __bread_gfp+0x216/0x3c0 fs/buffer.c:1518 sb_bread include/linux/buffer_head.h:346 [inline] udf_check_vsd fs/udf/super.c:772 [inline] udf_load_vrs+0x365/0xf20 fs/udf/super.c:2015 udf_fill_super+0x5ad/0x17a0 fs/udf/super.c:2201 get_tree_bdev_flags+0x40e/0x4d0 fs/super.c:1691 vfs_get_tree+0x92/0x2b0 fs/super.c:1751 fc_mount fs/namespace.c:1274 [inline] do_new_mount_fc fs/namespace.c:3726 [inline] do_new_mount+0x302/0xa10 fs/namespace.c:3802 do_mount fs/namespace.c:4125 [inline] __do_sys_mount fs/namespace.c:4324 [inline] __se_sys_mount+0x313/0x410 fs/namespace.c:4301 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 -> #5 (&nsock->tx_lock){+.+.}-{4:4}: 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 nbd_handle_cmd drivers/block/nbd.c:1140 [inline] nbd_queue_rq+0x257/0xf10 drivers/block/nbd.c:1204 blk_mq_dispatch_rq_list+0x4c0/0x1900 block/blk-mq.c:2129 __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+0xda4/0x1570 block/blk-mq-sched.c:307 blk_mq_sched_dispatch_requests+0xd7/0x190 block/blk-mq-sched.c:329 blk_mq_run_hw_queue+0x348/0x4f0 block/blk-mq.c:2367 blk_mq_dispatch_list+0xd0c/0xe00 include/linux/spinlock.h:-1 blk_mq_flush_plug_list+0x469/0x550 block/blk-mq.c:2976 __blk_flush_plug+0x3d3/0x4b0 block/blk-core.c:1223 blk_finish_plug block/blk-core.c:1250 [inline] __submit_bio+0x2d3/0x5a0 block/blk-core.c:649 __submit_bio_noacct_mq block/blk-core.c:722 [inline] submit_bio_noacct_nocheck+0x2fb/0xa50 block/blk-core.c:753 submit_bio_wait+0x104/0x200 block/bio.c:1389 bdev_rw_virt+0x331/0x4c0 block/bio.c:1420 hib_submit_io_sync kernel/power/swap.c:273 [inline] swsusp_check+0xe1/0x440 kernel/power/swap.c:1581 software_resume+0x51/0x420 kernel/power/hibernate.c:1040 resume_store+0x2f1/0x460 kernel/power/hibernate.c:1325 kernfs_fop_write_iter+0x3af/0x540 fs/kernfs/file.c:352 new_sync_write fs/read_write.c:593 [inline] vfs_write+0x5c9/0xb30 fs/read_write.c:686 ksys_write+0x145/0x250 fs/read_write.c:738 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 -> #4 (&cmd->lock){+.+.}-{4:4}: 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 nbd_queue_rq+0xc8/0xf10 drivers/block/nbd.c:1196 blk_mq_dispatch_rq_list+0x4c0/0x1900 block/blk-mq.c:2129 __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+0xda4/0x1570 block/blk-mq-sched.c:307 blk_mq_sched_dispatch_requests+0xd7/0x190 block/blk-mq-sched.c:329 blk_mq_run_hw_queue+0x348/0x4f0 block/blk-mq.c:2367 blk_mq_dispatch_list+0xd0c/0xe00 include/linux/spinlock.h:-1 blk_mq_flush_plug_list+0x469/0x550 block/blk-mq.c:2976 __blk_flush_plug+0x3d3/0x4b0 block/blk-core.c:1223 blk_finish_plug block/blk-core.c:1250 [inline] __submit_bio+0x2d3/0x5a0 block/blk-core.c:649 __submit_bio_noacct_mq block/blk-core.c:722 [inline] submit_bio_noacct_nocheck+0x2fb/0xa50 block/blk-core.c:753 submit_bh fs/buffer.c:2829 [inline] __bread_slow fs/buffer.c:1272 [inline] __bread_gfp+0x216/0x3c0 fs/buffer.c:1518 sb_bread include/linux/buffer_head.h:346 [inline] vxfs_try_sb_magic+0xd7/0x360 fs/freevxfs/vxfs_super.c:134 vxfs_fill_super+0x17d/0x870 fs/freevxfs/vxfs_super.c:213 get_tree_bdev_flags+0x40e/0x4d0 fs/super.c:1691 vfs_get_tree+0x92/0x2b0 fs/super.c:1751 fc_mount fs/namespace.c:1274 [inline] do_new_mount_fc fs/namespace.c:3726 [inline] do_new_mount+0x302/0xa10 fs/namespace.c:3802 do_mount fs/namespace.c:4125 [inline] __do_sys_mount fs/namespace.c:4324 [inline] __se_sys_mount+0x313/0x410 fs/namespace.c:4301 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 -> #3 (set->srcu){.+.+}-{0:0}: lock_sync+0xba/0x160 kernel/locking/lockdep.c:5916 srcu_lock_sync include/linux/srcu.h:173 [inline] __synchronize_srcu+0x96/0x3a0 kernel/rcu/srcutree.c:1429 elevator_switch+0x12b/0x640 block/elevator.c:588 elevator_change+0x315/0x4c0 block/elevator.c:691 elevator_set_default+0x186/0x260 block/elevator.c:767 blk_register_queue+0x34e/0x3f0 block/blk-sysfs.c:942 __add_disk+0x677/0xd50 block/genhd.c:528 add_disk_fwnode+0xfc/0x480 block/genhd.c:597 add_disk include/linux/blkdev.h:775 [inline] nbd_dev_add+0x717/0xae0 drivers/block/nbd.c:1981 nbd_init+0x168/0x1f0 drivers/block/nbd.c:2688 do_one_initcall+0x236/0x820 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+0x4bc/0x870 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}: 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 elevator_change+0x1e5/0x4c0 block/elevator.c:689 elevator_set_none+0x42/0xb0 block/elevator.c:782 blk_mq_elv_switch_none block/blk-mq.c:5034 [inline] __blk_mq_update_nr_hw_queues block/blk-mq.c:5077 [inline] blk_mq_update_nr_hw_queues+0x598/0x1ab0 block/blk-mq.c:5135 nbd_start_device+0x17f/0xb10 drivers/block/nbd.c:1486 nbd_genl_connect+0x135b/0x18f0 drivers/block/nbd.c:2236 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:2552 genl_rcv+0x28/0x40 net/netlink/genetlink.c:1219 netlink_unicast_kernel net/netlink/af_netlink.c:1320 [inline] netlink_unicast+0x82f/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:2617 ___sys_sendmsg+0x21f/0x2a0 net/socket.c:2671 __sys_sendmsg net/socket.c:2703 [inline] __do_sys_sendmsg net/socket.c:2708 [inline] __se_sys_sendmsg net/socket.c:2706 [inline] __x64_sys_sendmsg+0x19b/0x260 net/socket.c:2706 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 -> #1 (&q->q_usage_counter(io)#50){++++}-{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:4401 [inline] __blk_mq_alloc_disk+0x15c/0x340 block/blk-mq.c:4448 nbd_dev_add+0x46c/0xae0 drivers/block/nbd.c:1951 nbd_init+0x168/0x1f0 drivers/block/nbd.c:2688 do_one_initcall+0x236/0x820 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+0x4bc/0x870 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: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 __fs_reclaim_acquire mm/page_alloc.c:4245 [inline] fs_reclaim_acquire+0x72/0x100 mm/page_alloc.c:4259 might_alloc include/linux/sched/mm.h:318 [inline] slab_pre_alloc_hook mm/slub.c:4721 [inline] slab_alloc_node mm/slub.c:5044 [inline] kmem_cache_alloc_lru_noprof+0x4a/0x6d0 mm/slub.c:5087 sock_alloc_inode+0x28/0xc0 net/socket.c:309 alloc_inode+0x6a/0x1b0 fs/inode.c:346 new_inode_pseudo include/linux/fs.h:3398 [inline] sock_alloc net/socket.c:624 [inline] __sock_create+0x12d/0x9f0 net/socket.c:1556 mptcp_subflow_create_socket+0xf0/0x7d0 net/mptcp/subflow.c:1764 __mptcp_subflow_connect+0x21f/0x1a00 net/mptcp/subflow.c:1619 mptcp_pm_create_subflow_or_signal_addr+0xe4d/0x1c30 net/mptcp/pm_kernel.c:364 mptcp_pm_nl_fully_established net/mptcp/pm_kernel.c:372 [inline] __mptcp_pm_kernel_worker+0x3f3/0xfb0 net/mptcp/pm_kernel.c:1351 mptcp_pm_worker+0x1b9/0x2d0 net/mptcp/pm.c:1004 mptcp_worker+0xd5/0x1160 net/mptcp/protocol.c:2746 process_one_work kernel/workqueue.c:3263 [inline] process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3346 worker_thread+0x8a0/0xda0 kernel/workqueue.c:3427 kthread+0x711/0x8a0 kernel/kthread.c:463 ret_from_fork+0x4bc/0x870 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 --> &nsock->tx_lock --> sk_lock-AF_INET Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(sk_lock-AF_INET); lock(&nsock->tx_lock); lock(sk_lock-AF_INET); lock(fs_reclaim); *** DEADLOCK *** 3 locks held by kworker/0:6/5961: #0: ffff88801a871548 ((wq_completion)events){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3238 [inline] #0: ffff88801a871548 ((wq_completion)events){+.+.}-{0:0}, at: process_scheduled_works+0x9b4/0x17b0 kernel/workqueue.c:3346 #1: ffffc90004d9fba0 ((work_completion)(&msk->work)){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3239 [inline] #1: ffffc90004d9fba0 ((work_completion)(&msk->work)){+.+.}-{0:0}, at: process_scheduled_works+0x9ef/0x17b0 kernel/workqueue.c:3346 #2: ffff88806f30ca60 (sk_lock-AF_INET){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1676 [inline] #2: ffff88806f30ca60 (sk_lock-AF_INET){+.+.}-{0:0}, at: mptcp_worker+0x36/0x1160 net/mptcp/protocol.c:2739 stack backtrace: CPU: 0 UID: 0 PID: 5961 Comm: kworker/0:6 Not tainted syzkaller #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025 Workqueue: events mptcp_worker Call Trace: 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 __fs_reclaim_acquire mm/page_alloc.c:4245 [inline] fs_reclaim_acquire+0x72/0x100 mm/page_alloc.c:4259 might_alloc include/linux/sched/mm.h:318 [inline] slab_pre_alloc_hook mm/slub.c:4721 [inline] slab_alloc_node mm/slub.c:5044 [inline] kmem_cache_alloc_lru_noprof+0x4a/0x6d0 mm/slub.c:5087 sock_alloc_inode+0x28/0xc0 net/socket.c:309 alloc_inode+0x6a/0x1b0 fs/inode.c:346 new_inode_pseudo include/linux/fs.h:3398 [inline] sock_alloc net/socket.c:624 [inline] __sock_create+0x12d/0x9f0 net/socket.c:1556 mptcp_subflow_create_socket+0xf0/0x7d0 net/mptcp/subflow.c:1764 __mptcp_subflow_connect+0x21f/0x1a00 net/mptcp/subflow.c:1619 mptcp_pm_create_subflow_or_signal_addr+0xe4d/0x1c30 net/mptcp/pm_kernel.c:364 mptcp_pm_nl_fully_established net/mptcp/pm_kernel.c:372 [inline] __mptcp_pm_kernel_worker+0x3f3/0xfb0 net/mptcp/pm_kernel.c:1351 mptcp_pm_worker+0x1b9/0x2d0 net/mptcp/pm.c:1004 mptcp_worker+0xd5/0x1160 net/mptcp/protocol.c:2746 process_one_work kernel/workqueue.c:3263 [inline] process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3346 worker_thread+0x8a0/0xda0 kernel/workqueue.c:3427 kthread+0x711/0x8a0 kernel/kthread.c:463 ret_from_fork+0x4bc/0x870 arch/x86/kernel/process.c:158 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245