syzbot

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Tainted: G             L     
------------------------------------------------------
kworker/u8:21/30171 is trying to acquire lock:
ffffffff8edb7120 (fs_reclaim){+.+.}-{0:0}, at: might_alloc include/linux/sched/mm.h:317 [inline]
ffffffff8edb7120 (fs_reclaim){+.+.}-{0:0}, at: slab_pre_alloc_hook mm/slub.c:4565 [inline]
ffffffff8edb7120 (fs_reclaim){+.+.}-{0:0}, at: slab_alloc_node mm/slub.c:4925 [inline]
ffffffff8edb7120 (fs_reclaim){+.+.}-{0:0}, at: kmem_cache_alloc_node_noprof+0x66/0x6b0 mm/slub.c:5017

but task is already holding lock:
ffff8880517de0e0 (k-sk_lock-AF_INET6){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1713 [inline]
ffff8880517de0e0 (k-sk_lock-AF_INET6){+.+.}-{0:0}, at: inet_stream_connect+0x43/0xa0 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_acquire kernel/locking/lockdep.c:5868 [inline]
       lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825
       lock_sock_nested+0x41/0xf0 net/core/sock.c:3825
       lock_sock include/net/sock.h:1713 [inline]
       __inet6_bind+0x80f/0x1b40 net/ipv6/af_inet6.c:292
       inet6_bind_sk net/ipv6/af_inet6.c:449 [inline]
       inet6_bind_sk+0xb8/0xf0 net/ipv6/af_inet6.c:426
       mptcp_bind+0x135/0x1e0 net/mptcp/protocol.c:4116
       __sys_bind_socket net/socket.c:1920 [inline]
       __sys_bind_socket net/socket.c:1912 [inline]
       __sys_bind+0x1a9/0x260 net/socket.c:1951
       __do_sys_bind net/socket.c:1956 [inline]
       __se_sys_bind net/socket.c:1954 [inline]
       __x64_sys_bind+0x72/0xb0 net/socket.c:1954
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #6 (sk_lock-AF_INET6){+.+.}-{0:0}:
       lock_acquire kernel/locking/lockdep.c:5868 [inline]
       lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825
       lock_sock_nested+0x41/0xf0 net/core/sock.c:3825
       lock_sock include/net/sock.h:1713 [inline]
       inet_shutdown+0x67/0x410 net/ipv4/af_inet.c:913
       nbd_mark_nsock_dead+0xae/0x5c0 drivers/block/nbd.c:318
       recv_work+0x5fb/0x8c0 drivers/block/nbd.c:1021
       process_one_work+0xa23/0x1940 kernel/workqueue.c:3322
       process_scheduled_works kernel/workqueue.c:3405 [inline]
       worker_thread+0x5ef/0xe50 kernel/workqueue.c:3486
       kthread+0x370/0x450 kernel/kthread.c:436
       ret_from_fork+0x72b/0xd50 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}:
       lock_acquire kernel/locking/lockdep.c:5868 [inline]
       lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x1a4/0x1bd0 kernel/locking/mutex.c:821
       nbd_handle_cmd drivers/block/nbd.c:1143 [inline]
       nbd_queue_rq+0x428/0x1080 drivers/block/nbd.c:1207
       blk_mq_dispatch_rq_list+0x422/0x1e70 block/blk-mq.c:2117
       __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+0xcea/0x1620 block/blk-mq-sched.c:307
       blk_mq_sched_dispatch_requests+0xd7/0x1c0 block/blk-mq-sched.c:329
       blk_mq_run_work_fn+0x135/0x380 block/blk-mq.c:2531
       process_one_work+0xa23/0x1940 kernel/workqueue.c:3322
       process_scheduled_works kernel/workqueue.c:3405 [inline]
       worker_thread+0x5ef/0xe50 kernel/workqueue.c:3486
       kthread+0x370/0x450 kernel/kthread.c:436
       ret_from_fork+0x72b/0xd50 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #4 (&cmd->lock){+.+.}-{4:4}:
       lock_acquire kernel/locking/lockdep.c:5868 [inline]
       lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x1a4/0x1bd0 kernel/locking/mutex.c:821
       nbd_queue_rq+0xba/0x1080 drivers/block/nbd.c:1199
       blk_mq_dispatch_rq_list+0x422/0x1e70 block/blk-mq.c:2117
       __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+0xcea/0x1620 block/blk-mq-sched.c:307
       blk_mq_sched_dispatch_requests+0xd7/0x1c0 block/blk-mq-sched.c:329
       blk_mq_run_work_fn+0x135/0x380 block/blk-mq.c:2531
       process_one_work+0xa23/0x1940 kernel/workqueue.c:3322
       process_scheduled_works kernel/workqueue.c:3405 [inline]
       worker_thread+0x5ef/0xe50 kernel/workqueue.c:3486
       kthread+0x370/0x450 kernel/kthread.c:436
       ret_from_fork+0x72b/0xd50 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #3 (set->srcu){.+.+}-{0:0}:
       lock_sync kernel/locking/lockdep.c:5916 [inline]
       lock_sync+0x9d/0x110 kernel/locking/lockdep.c:5904
       srcu_lock_sync include/linux/srcu.h:199 [inline]
       __synchronize_srcu+0xa2/0x300 kernel/rcu/srcutree.c:1481
       blk_mq_wait_quiesce_done block/blk-mq.c:284 [inline]
       blk_mq_wait_quiesce_done block/blk-mq.c:281 [inline]
       blk_mq_quiesce_queue block/blk-mq.c:304 [inline]
       blk_mq_quiesce_queue+0x149/0x1c0 block/blk-mq.c:299
       elevator_switch+0x17b/0x7e0 block/elevator.c:576
       elevator_change+0x352/0x530 block/elevator.c:681
       elevator_set_default+0x29e/0x360 block/elevator.c:754
       blk_register_queue+0x48e/0x630 block/blk-sysfs.c:992
       __add_disk+0x73f/0xe40 block/genhd.c:528
       add_disk_fwnode+0x118/0x5c0 block/genhd.c:597
       add_disk include/linux/blkdev.h:800 [inline]
       nbd_dev_add+0x77a/0xb10 drivers/block/nbd.c:2021
       nbd_init+0x291/0x2b0 drivers/block/nbd.c:2729
       do_one_initcall+0x11d/0x700 init/main.c:1347
       do_initcall_level init/main.c:1409 [inline]
       do_initcalls init/main.c:1425 [inline]
       do_basic_setup init/main.c:1445 [inline]
       kernel_init_freeable+0x6ea/0x7b0 init/main.c:1658
       kernel_init+0x1f/0x1e0 init/main.c:1548
       ret_from_fork+0x72b/0xd50 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 kernel/locking/lockdep.c:5868 [inline]
       lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x1a4/0x1bd0 kernel/locking/mutex.c:821
       elevator_change+0x1bc/0x530 block/elevator.c:679
       elevator_set_none+0x92/0xf0 block/elevator.c:769
       blk_mq_elv_switch_none block/blk-mq.c:5101 [inline]
       __blk_mq_update_nr_hw_queues block/blk-mq.c:5146 [inline]
       blk_mq_update_nr_hw_queues+0x4c1/0x15f0 block/blk-mq.c:5211
       nbd_start_device+0x1a6/0xbd0 drivers/block/nbd.c:1526
       nbd_genl_connect+0xff2/0x1a40 drivers/block/nbd.c:2276
       genl_family_rcv_msg_doit+0x214/0x300 net/netlink/genetlink.c:1114
       genl_family_rcv_msg net/netlink/genetlink.c:1194 [inline]
       genl_rcv_msg+0x560/0x800 net/netlink/genetlink.c:1209
       netlink_rcv_skb+0x159/0x420 net/netlink/af_netlink.c:2556
       genl_rcv+0x28/0x40 net/netlink/genetlink.c:1218
       netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline]
       netlink_unicast+0x585/0x850 net/netlink/af_netlink.c:1345
       netlink_sendmsg+0x8b0/0xda0 net/netlink/af_netlink.c:1900
       sock_sendmsg_nosec net/socket.c:775 [inline]
       __sock_sendmsg net/socket.c:790 [inline]
       ____sys_sendmsg+0xa4d/0xbe0 net/socket.c:2684
       ___sys_sendmsg+0x190/0x1e0 net/socket.c:2738
       __sys_sendmsg+0x160/0x210 net/socket.c:2770
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x115/0x870 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 kernel/locking/lockdep.c:5868 [inline]
       lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825
       blk_alloc_queue+0x610/0x790 block/blk-core.c:504
       blk_mq_alloc_queue+0x174/0x290 block/blk-mq.c:4420
       __blk_mq_alloc_disk+0x29/0x120 block/blk-mq.c:4467
       nbd_dev_add+0x492/0xb10 drivers/block/nbd.c:1991
       nbd_init+0x291/0x2b0 drivers/block/nbd.c:2729
       do_one_initcall+0x11d/0x700 init/main.c:1347
       do_initcall_level init/main.c:1409 [inline]
       do_initcalls init/main.c:1425 [inline]
       do_basic_setup init/main.c:1445 [inline]
       kernel_init_freeable+0x6ea/0x7b0 init/main.c:1658
       kernel_init+0x1f/0x1e0 init/main.c:1548
       ret_from_fork+0x72b/0xd50 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+0xeb/0xe60 kernel/locking/lockdep.c:3165
       check_prevs_add kernel/locking/lockdep.c:3284 [inline]
       validate_chain kernel/locking/lockdep.c:3908 [inline]
       __lock_acquire+0x136c/0x1a40 kernel/locking/lockdep.c:5237
       lock_acquire kernel/locking/lockdep.c:5868 [inline]
       lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825
       __fs_reclaim_acquire mm/page_alloc.c:4329 [inline]
       fs_reclaim_acquire+0xc4/0x100 mm/page_alloc.c:4343
       might_alloc include/linux/sched/mm.h:317 [inline]
       slab_pre_alloc_hook mm/slub.c:4565 [inline]
       slab_alloc_node mm/slub.c:4925 [inline]
       kmem_cache_alloc_node_noprof+0x66/0x6b0 mm/slub.c:5017
       __alloc_skb+0x140/0x710 net/core/skbuff.c:704
       alloc_skb_fclone include/linux/skbuff.h:1434 [inline]
       tcp_stream_alloc_skb+0x34/0x660 net/ipv4/tcp.c:931
       tcp_connect+0xf22/0x5510 net/ipv4/tcp_output.c:4363
       tcp_v6_connect+0x1831/0x2660 net/ipv6/tcp_ipv6.c:346
       __inet_stream_connect+0x208/0xfa0 net/ipv4/af_inet.c:684
       inet_stream_connect+0x57/0xa0 net/ipv4/af_inet.c:755
       kernel_connect+0x107/0x160 net/socket.c:3726
       rds_tcp_conn_path_connect+0x72b/0xaa0 net/rds/tcp_connect.c:205
       rds_connect_worker+0x1b4/0x2d0 net/rds/threads.c:176
       process_one_work+0xa23/0x1940 kernel/workqueue.c:3322
       process_scheduled_works kernel/workqueue.c:3405 [inline]
       worker_thread+0x5ef/0xe50 kernel/workqueue.c:3486
       kthread+0x370/0x450 kernel/kthread.c:436
       ret_from_fork+0x72b/0xd50 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/u8:21/30171:
 #0: ffff8880398ac140 ((wq_completion)krds_cp_wq#11/0#2){+.+.}-{0:0}, at: process_one_work+0x12b1/0x1940 kernel/workqueue.c:3297
 #1: ffffc90005ad7d08 ((work_completion)(&(&cp->cp_conn_w)->work)){+.+.}-{0:0}, at: process_one_work+0x988/0x1940 kernel/workqueue.c:3298
 #2: ffff8880776d0c80 (&tc->t_conn_path_lock){+.+.}-{4:4}, at: rds_tcp_conn_path_connect+0x1da/0xaa0 net/rds/tcp_connect.c:118
 #3: ffff8880517de0e0 (k-sk_lock-AF_INET6){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1713 [inline]
 #3: ffff8880517de0e0 (k-sk_lock-AF_INET6){+.+.}-{0:0}, at: inet_stream_connect+0x43/0xa0 net/ipv4/af_inet.c:754

stack backtrace:
CPU: 1 UID: 0 PID: 30171 Comm: kworker/u8:21 Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/10/2026
Workqueue: krds_cp_wq#11/0 rds_connect_worker
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
 print_circular_bug.cold+0x178/0x1c7 kernel/locking/lockdep.c:2043
 check_noncircular+0x146/0x160 kernel/locking/lockdep.c:2175
 check_prev_add+0xeb/0xe60 kernel/locking/lockdep.c:3165
 check_prevs_add kernel/locking/lockdep.c:3284 [inline]
 validate_chain kernel/locking/lockdep.c:3908 [inline]
 __lock_acquire+0x136c/0x1a40 kernel/locking/lockdep.c:5237
 lock_acquire kernel/locking/lockdep.c:5868 [inline]
 lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825
 __fs_reclaim_acquire mm/page_alloc.c:4329 [inline]
 fs_reclaim_acquire+0xc4/0x100 mm/page_alloc.c:4343
 might_alloc include/linux/sched/mm.h:317 [inline]
 slab_pre_alloc_hook mm/slub.c:4565 [inline]
 slab_alloc_node mm/slub.c:4925 [inline]
 kmem_cache_alloc_node_noprof+0x66/0x6b0 mm/slub.c:5017
 __alloc_skb+0x140/0x710 net/core/skbuff.c:704
 alloc_skb_fclone include/linux/skbuff.h:1434 [inline]
 tcp_stream_alloc_skb+0x34/0x660 net/ipv4/tcp.c:931
 tcp_connect+0xf22/0x5510 net/ipv4/tcp_output.c:4363
 tcp_v6_connect+0x1831/0x2660 net/ipv6/tcp_ipv6.c:346
 __inet_stream_connect+0x208/0xfa0 net/ipv4/af_inet.c:684
 inet_stream_connect+0x57/0xa0 net/ipv4/af_inet.c:755
 kernel_connect+0x107/0x160 net/socket.c:3726
 rds_tcp_conn_path_connect+0x72b/0xaa0 net/rds/tcp_connect.c:205
 rds_connect_worker+0x1b4/0x2d0 net/rds/threads.c:176
 process_one_work+0xa23/0x1940 kernel/workqueue.c:3322
 process_scheduled_works kernel/workqueue.c:3405 [inline]
 worker_thread+0x5ef/0xe50 kernel/workqueue.c:3486
 kthread+0x370/0x450 kernel/kthread.c:436
 ret_from_fork+0x72b/0xd50 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>
bridge0: port 2(bridge_slave_1) entered blocking state
bridge0: port 2(bridge_slave_1) entered forwarding state