syzbot

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Tainted: G             L     
------------------------------------------------------
kworker/u8:0/12 is trying to acquire lock:
ffffffff8ea85420 (fs_reclaim){+.+.}-{0:0}, at: might_alloc include/linux/sched/mm.h:317 [inline]
ffffffff8ea85420 (fs_reclaim){+.+.}-{0:0}, at: slab_pre_alloc_hook mm/slub.c:4520 [inline]
ffffffff8ea85420 (fs_reclaim){+.+.}-{0:0}, at: slab_alloc_node mm/slub.c:4875 [inline]
ffffffff8ea85420 (fs_reclaim){+.+.}-{0:0}, at: kmem_cache_alloc_node_noprof+0x4a/0x690 mm/slub.c:4950

but task is already holding lock:
ffff8880326ed360 (k-sk_lock-AF_INET6){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1713 [inline]
ffff8880326ed360 (k-sk_lock-AF_INET6){+.+.}-{0:0}, at: inet_stream_connect+0x51/0xa0 net/ipv4/af_inet.c:754

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #7 (k-sk_lock-AF_INET6){+.+.}-{0:0}:
       lock_sock_nested+0x41/0x100 net/core/sock.c:3783
       lock_sock include/net/sock.h:1713 [inline]
       __inet6_bind+0x30c/0xf60 net/ipv6/af_inet6.c:292
       mptcp_bind+0x110/0x1d0 net/mptcp/protocol.c:4093
       __sys_bind_socket net/socket.c:1933 [inline]
       __sys_bind+0x2e3/0x410 net/socket.c:1964
       __do_sys_bind net/socket.c:1969 [inline]
       __se_sys_bind net/socket.c:1967 [inline]
       __x64_sys_bind+0x7a/0x90 net/socket.c:1967
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x15f/0xf80 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #6 (sk_lock-AF_INET6){+.+.}-{0:0}:
       lock_sock_nested+0x41/0x100 net/core/sock.c:3783
       lock_sock include/net/sock.h:1713 [inline]
       inet_shutdown+0x6a/0x390 net/ipv4/af_inet.c:915
       nbd_mark_nsock_dead+0x2e9/0x560 drivers/block/nbd.c:318
       sock_shutdown+0x15e/0x260 drivers/block/nbd.c:411
       nbd_clear_sock+0x24/0x170 drivers/block/nbd.c:1427
       nbd_config_put+0x2dd/0x580 drivers/block/nbd.c:1451
       nbd_genl_connect+0x19d5/0x1cf0 drivers/block/nbd.c:2248
       genl_family_rcv_msg_doit+0x22a/0x330 net/netlink/genetlink.c:1114
       genl_family_rcv_msg net/netlink/genetlink.c:1194 [inline]
       genl_rcv_msg+0x61c/0x7a0 net/netlink/genetlink.c:1209
       netlink_rcv_skb+0x232/0x4b0 net/netlink/af_netlink.c:2550
       genl_rcv+0x28/0x40 net/netlink/genetlink.c:1218
       netlink_unicast_kernel net/netlink/af_netlink.c:1318 [inline]
       netlink_unicast+0x75c/0x8e0 net/netlink/af_netlink.c:1344
       netlink_sendmsg+0x813/0xb40 net/netlink/af_netlink.c:1894
       sock_sendmsg_nosec net/socket.c:787 [inline]
       __sock_sendmsg net/socket.c:802 [inline]
       ____sys_sendmsg+0x972/0x9f0 net/socket.c:2698
       ___sys_sendmsg+0x2a5/0x360 net/socket.c:2752
       __sys_sendmsg net/socket.c:2784 [inline]
       __do_sys_sendmsg net/socket.c:2789 [inline]
       __se_sys_sendmsg net/socket.c:2787 [inline]
       __x64_sys_sendmsg+0x1bd/0x2a0 net/socket.c:2787
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x15f/0xf80 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #5 (&nsock->tx_lock){+.+.}-{4:4}:
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x1a3/0x1550 kernel/locking/mutex.c:820
       nbd_handle_cmd drivers/block/nbd.c:1143 [inline]
       nbd_queue_rq+0x37b/0x1100 drivers/block/nbd.c:1207
       blk_mq_dispatch_rq_list+0xa70/0x1910 block/blk-mq.c:2148
       __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+0xdcc/0x1600 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:2386
       blk_mq_dispatch_list+0xd16/0xe10 include/linux/spinlock.h:-1
       blk_mq_flush_plug_list+0x48d/0x570 block/blk-mq.c:2997
       __blk_flush_plug+0x3ed/0x4d0 block/blk-core.c:1230
       blk_finish_plug block/blk-core.c:1257 [inline]
       __submit_bio+0x28d/0x580 block/blk-core.c:649
       __submit_bio_noacct_mq block/blk-core.c:722 [inline]
       submit_bio_noacct_nocheck+0x2f4/0xa40 block/blk-core.c:753
       submit_bh fs/buffer.c:2742 [inline]
       block_read_full_folio+0x599/0x830 fs/buffer.c:2344
       filemap_read_folio+0x137/0x3b0 mm/filemap.c:2502
       do_read_cache_folio+0x358/0x590 mm/filemap.c:4107
       read_mapping_folio include/linux/pagemap.h:1017 [inline]
       read_part_sector+0xb6/0x2b0 block/partitions/core.c:724
       adfspart_check_ICS+0xb1/0x960 block/partitions/acorn.c:356
       check_partition block/partitions/core.c:143 [inline]
       blk_add_partitions block/partitions/core.c:591 [inline]
       bdev_disk_changed+0x817/0x1770 block/partitions/core.c:695
       blkdev_get_whole+0x380/0x510 block/bdev.c:756
       bdev_open+0x31e/0xd30 block/bdev.c:965
       blkdev_open+0x470/0x610 block/fops.c:697
       do_dentry_open+0x785/0x14e0 fs/open.c:947
       vfs_open+0x3b/0x340 fs/open.c:1079
       do_open fs/namei.c:4699 [inline]
       path_openat+0x2e08/0x3860 fs/namei.c:4858
       do_file_open+0x23e/0x4a0 fs/namei.c:4887
       do_sys_openat2+0x113/0x200 fs/open.c:1364
       do_sys_open fs/open.c:1370 [inline]
       __do_sys_openat fs/open.c:1386 [inline]
       __se_sys_openat fs/open.c:1381 [inline]
       __x64_sys_openat+0x138/0x170 fs/open.c:1381
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x15f/0xf80 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #4 (&cmd->lock){+.+.}-{4:4}:
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x1a3/0x1550 kernel/locking/mutex.c:820
       nbd_queue_rq+0xc6/0x1100 drivers/block/nbd.c:1199
       blk_mq_dispatch_rq_list+0xa70/0x1910 block/blk-mq.c:2148
       __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+0xdcc/0x1600 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:2386
       blk_mq_dispatch_list+0xd16/0xe10 include/linux/spinlock.h:-1
       blk_mq_flush_plug_list+0x48d/0x570 block/blk-mq.c:2997
       __blk_flush_plug+0x3ed/0x4d0 block/blk-core.c:1230
       blk_finish_plug block/blk-core.c:1257 [inline]
       __submit_bio+0x28d/0x580 block/blk-core.c:649
       __submit_bio_noacct_mq block/blk-core.c:722 [inline]
       submit_bio_noacct_nocheck+0x2f4/0xa40 block/blk-core.c:753
       submit_bh fs/buffer.c:2742 [inline]
       block_read_full_folio+0x599/0x830 fs/buffer.c:2344
       filemap_read_folio+0x137/0x3b0 mm/filemap.c:2502
       do_read_cache_folio+0x358/0x590 mm/filemap.c:4107
       read_mapping_folio include/linux/pagemap.h:1017 [inline]
       read_part_sector+0xb6/0x2b0 block/partitions/core.c:724
       adfspart_check_ICS+0xb1/0x960 block/partitions/acorn.c:356
       check_partition block/partitions/core.c:143 [inline]
       blk_add_partitions block/partitions/core.c:591 [inline]
       bdev_disk_changed+0x817/0x1770 block/partitions/core.c:695
       blkdev_get_whole+0x380/0x510 block/bdev.c:756
       bdev_open+0x31e/0xd30 block/bdev.c:965
       blkdev_open+0x470/0x610 block/fops.c:697
       do_dentry_open+0x785/0x14e0 fs/open.c:947
       vfs_open+0x3b/0x340 fs/open.c:1079
       do_open fs/namei.c:4699 [inline]
       path_openat+0x2e08/0x3860 fs/namei.c:4858
       do_file_open+0x23e/0x4a0 fs/namei.c:4887
       do_sys_openat2+0x113/0x200 fs/open.c:1364
       do_sys_open fs/open.c:1370 [inline]
       __do_sys_openat fs/open.c:1386 [inline]
       __se_sys_openat fs/open.c:1381 [inline]
       __x64_sys_openat+0x138/0x170 fs/open.c:1381
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x15f/0xf80 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #3 (set->srcu){.+.+}-{0:0}:
       srcu_lock_sync include/linux/srcu.h:199 [inline]
       __synchronize_srcu+0xca/0x300 kernel/rcu/srcutree.c:1481
       elevator_switch+0x1e8/0x7a0 block/elevator.c:576
       elevator_change+0x2cc/0x450 block/elevator.c:681
       elevator_set_default+0x36c/0x430 block/elevator.c:754
       blk_register_queue+0x3e9/0x4e0 block/blk-sysfs.c:987
       __add_disk+0x677/0xd50 block/genhd.c:528
       add_disk_fwnode+0xfb/0x480 block/genhd.c:597
       add_disk include/linux/blkdev.h:794 [inline]
       nbd_dev_add+0x72c/0xb50 drivers/block/nbd.c:1984
       nbd_init+0x168/0x1f0 drivers/block/nbd.c:2692
       do_one_initcall+0x250/0x870 init/main.c:1392
       do_initcall_level+0x104/0x190 init/main.c:1454
       do_initcalls+0x59/0xa0 init/main.c:1470
       kernel_init_freeable+0x2a6/0x3e0 init/main.c:1703
       kernel_init+0x1d/0x1d0 init/main.c:1593
       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+0x1a3/0x1550 kernel/locking/mutex.c:820
       elevator_change+0x1b3/0x450 block/elevator.c:679
       elevator_set_none+0xb5/0x140 block/elevator.c:769
       blk_mq_elv_switch_none block/blk-mq.c:5150 [inline]
       __blk_mq_update_nr_hw_queues block/blk-mq.c:5195 [inline]
       blk_mq_update_nr_hw_queues+0x5e7/0x1a60 block/blk-mq.c:5260
       nbd_start_device+0x17f/0xb10 drivers/block/nbd.c:1489
       nbd_genl_connect+0x165b/0x1cf0 drivers/block/nbd.c:2239
       genl_family_rcv_msg_doit+0x22a/0x330 net/netlink/genetlink.c:1114
       genl_family_rcv_msg net/netlink/genetlink.c:1194 [inline]
       genl_rcv_msg+0x61c/0x7a0 net/netlink/genetlink.c:1209
       netlink_rcv_skb+0x232/0x4b0 net/netlink/af_netlink.c:2550
       genl_rcv+0x28/0x40 net/netlink/genetlink.c:1218
       netlink_unicast_kernel net/netlink/af_netlink.c:1318 [inline]
       netlink_unicast+0x75c/0x8e0 net/netlink/af_netlink.c:1344
       netlink_sendmsg+0x813/0xb40 net/netlink/af_netlink.c:1894
       sock_sendmsg_nosec net/socket.c:787 [inline]
       __sock_sendmsg net/socket.c:802 [inline]
       ____sys_sendmsg+0x972/0x9f0 net/socket.c:2698
       ___sys_sendmsg+0x2a5/0x360 net/socket.c:2752
       __sys_sendmsg net/socket.c:2784 [inline]
       __do_sys_sendmsg net/socket.c:2789 [inline]
       __se_sys_sendmsg net/socket.c:2787 [inline]
       __x64_sys_sendmsg+0x1bd/0x2a0 net/socket.c:2787
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x15f/0xf80 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (&q->q_usage_counter(io)#54){++++}-{0:0}:
       blk_alloc_queue+0x546/0x680 block/blk-core.c:461
       blk_mq_alloc_queue block/blk-mq.c:4469 [inline]
       __blk_mq_alloc_disk+0x197/0x390 block/blk-mq.c:4516
       nbd_dev_add+0x499/0xb50 drivers/block/nbd.c:1954
       nbd_init+0x168/0x1f0 drivers/block/nbd.c:2692
       do_one_initcall+0x250/0x870 init/main.c:1392
       do_initcall_level+0x104/0x190 init/main.c:1454
       do_initcalls+0x59/0xa0 init/main.c:1470
       kernel_init_freeable+0x2a6/0x3e0 init/main.c:1703
       kernel_init+0x1d/0x1d0 init/main.c:1593
       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:3165 [inline]
       check_prevs_add kernel/locking/lockdep.c:3284 [inline]
       validate_chain kernel/locking/lockdep.c:3908 [inline]
       __lock_acquire+0x15a5/0x2cf0 kernel/locking/lockdep.c:5237
       lock_acquire+0x106/0x350 kernel/locking/lockdep.c:5868
       __fs_reclaim_acquire mm/page_alloc.c:4325 [inline]
       fs_reclaim_acquire+0x71/0x100 mm/page_alloc.c:4339
       might_alloc include/linux/sched/mm.h:317 [inline]
       slab_pre_alloc_hook mm/slub.c:4520 [inline]
       slab_alloc_node mm/slub.c:4875 [inline]
       kmem_cache_alloc_node_noprof+0x4a/0x690 mm/slub.c:4950
       __alloc_skb+0x1d0/0x7d0 net/core/skbuff.c:702
       alloc_skb_fclone include/linux/skbuff.h:1433 [inline]
       tcp_stream_alloc_skb+0x3f/0x580 net/ipv4/tcp.c:935
       tcp_connect+0x15a9/0x53a0 net/ipv4/tcp_output.c:4357
       tcp_v6_connect+0x1295/0x1b10 net/ipv6/tcp_ipv6.c:338
       __inet_stream_connect+0x25a/0xdd0 net/ipv4/af_inet.c:684
       inet_stream_connect+0x66/0xa0 net/ipv4/af_inet.c:755
       kernel_connect+0x141/0x1c0 net/socket.c:3740
       rds_tcp_conn_path_connect+0x6f6/0x930 net/rds/tcp_connect.c:205
       rds_connect_worker+0x1d8/0x290 net/rds/threads.c:176
       process_one_work kernel/workqueue.c:3314 [inline]
       process_scheduled_works+0xb5d/0x1860 kernel/workqueue.c:3397
       worker_thread+0xa53/0xfc0 kernel/workqueue.c:3478
       kthread+0x389/0x470 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 --> sk_lock-AF_INET6 --> k-sk_lock-AF_INET6

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(k-sk_lock-AF_INET6);
                               lock(sk_lock-AF_INET6);
                               lock(k-sk_lock-AF_INET6);
  lock(fs_reclaim);

 *** DEADLOCK ***

4 locks held by kworker/u8:0/12:
 #0: ffff888034f94940 ((wq_completion)krds_cp_wq#7/0){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3289 [inline]
 #0: ffff888034f94940 ((wq_completion)krds_cp_wq#7/0){+.+.}-{0:0}, at: process_scheduled_works+0xa35/0x1860 kernel/workqueue.c:3397
 #1: ffffc90000117c40 ((work_completion)(&(&cp->cp_conn_w)->work)){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3290 [inline]
 #1: ffffc90000117c40 ((work_completion)(&(&cp->cp_conn_w)->work)){+.+.}-{0:0}, at: process_scheduled_works+0xa70/0x1860 kernel/workqueue.c:3397
 #2: ffff88804ec5de80 (&tc->t_conn_path_lock){+.+.}-{4:4}, at: rds_tcp_conn_path_connect+0x1cc/0x930 net/rds/tcp_connect.c:118
 #3: ffff8880326ed360 (k-sk_lock-AF_INET6){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1713 [inline]
 #3: ffff8880326ed360 (k-sk_lock-AF_INET6){+.+.}-{0:0}, at: inet_stream_connect+0x51/0xa0 net/ipv4/af_inet.c:754

stack backtrace:
CPU: 1 UID: 0 PID: 12 Comm: kworker/u8:0 Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
Workqueue: krds_cp_wq#7/0 rds_connect_worker
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_circular_bug+0x2e1/0x300 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+0x15a5/0x2cf0 kernel/locking/lockdep.c:5237
 lock_acquire+0x106/0x350 kernel/locking/lockdep.c:5868
 __fs_reclaim_acquire mm/page_alloc.c:4325 [inline]
 fs_reclaim_acquire+0x71/0x100 mm/page_alloc.c:4339
 might_alloc include/linux/sched/mm.h:317 [inline]
 slab_pre_alloc_hook mm/slub.c:4520 [inline]
 slab_alloc_node mm/slub.c:4875 [inline]
 kmem_cache_alloc_node_noprof+0x4a/0x690 mm/slub.c:4950
 __alloc_skb+0x1d0/0x7d0 net/core/skbuff.c:702
 alloc_skb_fclone include/linux/skbuff.h:1433 [inline]
 tcp_stream_alloc_skb+0x3f/0x580 net/ipv4/tcp.c:935
 tcp_connect+0x15a9/0x53a0 net/ipv4/tcp_output.c:4357
 tcp_v6_connect+0x1295/0x1b10 net/ipv6/tcp_ipv6.c:338
 __inet_stream_connect+0x25a/0xdd0 net/ipv4/af_inet.c:684
 inet_stream_connect+0x66/0xa0 net/ipv4/af_inet.c:755
 kernel_connect+0x141/0x1c0 net/socket.c:3740
 rds_tcp_conn_path_connect+0x6f6/0x930 net/rds/tcp_connect.c:205
 rds_connect_worker+0x1d8/0x290 net/rds/threads.c:176
 process_one_work kernel/workqueue.c:3314 [inline]
 process_scheduled_works+0xb5d/0x1860 kernel/workqueue.c:3397
 worker_thread+0xa53/0xfc0 kernel/workqueue.c:3478
 kthread+0x389/0x470 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
 </TASK>