syzbot

======================================================
WARNING: possible circular locking dependency detected
6.16.0-rc4-next-20250704-syzkaller #0 Not tainted
------------------------------------------------------
udevd/6083 is trying to acquire lock:
ffff88807b837870 (&nsock->tx_lock){+.+.}-{4:4}, at: nbd_handle_cmd drivers/block/nbd.c:1140 [inline]
ffff88807b837870 (&nsock->tx_lock){+.+.}-{4:4}, at: nbd_queue_rq+0x257/0xf10 drivers/block/nbd.c:1204

but task is already holding lock:
ffff8880597ee178 (&cmd->lock){+.+.}-{4:4}, at: nbd_queue_rq+0xc8/0xf10 drivers/block/nbd.c:1196

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #6 (&cmd->lock){+.+.}-{4:4}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5871
       __mutex_lock_common kernel/locking/mutex.c:602 [inline]
       __mutex_lock+0x182/0xe80 kernel/locking/mutex.c:747
       nbd_queue_rq+0xc8/0xf10 drivers/block/nbd.c:1196
       blk_mq_dispatch_rq_list+0x4c0/0x1900 block/blk-mq.c:2118
       __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:2356
       blk_mq_dispatch_list+0xd0c/0xe00 include/linux/spinlock.h:-1
       blk_mq_flush_plug_list+0x469/0x550 block/blk-mq.c:2965
       __blk_flush_plug+0x3d3/0x4b0 block/blk-core.c:1220
       blk_finish_plug block/blk-core.c:1247 [inline]
       __submit_bio+0x2d3/0x5a0 block/blk-core.c:649
       __submit_bio_noacct_mq block/blk-core.c:722 [inline]
       submit_bio_noacct_nocheck+0x4ab/0xb50 block/blk-core.c:751
       submit_bh fs/buffer.c:2829 [inline]
       block_read_full_folio+0x7b7/0x830 fs/buffer.c:2461
       filemap_read_folio+0x117/0x380 mm/filemap.c:2413
       do_read_cache_folio+0x350/0x590 mm/filemap.c:3957
       read_mapping_folio include/linux/pagemap.h:972 [inline]
       read_part_sector+0xb6/0x2b0 block/partitions/core.c:722
       adfspart_check_ICS+0xa4/0xa50 block/partitions/acorn.c:360
       check_partition block/partitions/core.c:141 [inline]
       blk_add_partitions block/partitions/core.c:589 [inline]
       bdev_disk_changed+0x75c/0x14b0 block/partitions/core.c:693
       blkdev_get_whole+0x380/0x510 block/bdev.c:748
       bdev_open+0x31e/0xd30 block/bdev.c:957
       blkdev_open+0x3a8/0x510 block/fops.c:676
       do_dentry_open+0xdf0/0x1970 fs/open.c:964
       vfs_open+0x3b/0x340 fs/open.c:1094
       do_open fs/namei.c:3887 [inline]
       path_openat+0x2ee5/0x3830 fs/namei.c:4046
       do_filp_open+0x1fa/0x410 fs/namei.c:4073
       do_sys_openat2+0x121/0x1c0 fs/open.c:1434
       do_sys_open fs/open.c:1449 [inline]
       __do_sys_openat fs/open.c:1465 [inline]
       __se_sys_openat fs/open.c:1460 [inline]
       __x64_sys_openat+0x138/0x170 fs/open.c:1460
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #5 (set->srcu){.+.+}-{0:0}:
       lock_sync+0xba/0x160 kernel/locking/lockdep.c:5919
       srcu_lock_sync include/linux/srcu.h:173 [inline]
       __synchronize_srcu+0x96/0x3a0 kernel/rcu/srcutree.c:1429
       elevator_switch+0x12b/0x5f0 block/elevator.c:587
       elevator_change+0x21b/0x320 block/elevator.c:679
       elevator_set_default+0x144/0x210 block/elevator.c:737
       blk_register_queue+0x35d/0x400 block/blk-sysfs.c:879
       __add_disk+0x677/0xd50 block/genhd.c:528
       add_disk_fwnode+0xfc/0x480 block/genhd.c:597
       add_disk include/linux/blkdev.h:765 [inline]
       nbd_dev_add+0x70e/0xb00 drivers/block/nbd.c:1963
       nbd_init+0x21a/0x2d0 drivers/block/nbd.c:2670
       do_one_initcall+0x233/0x820 init/main.c:1269
       do_initcall_level+0x137/0x1f0 init/main.c:1331
       do_initcalls+0x69/0xd0 init/main.c:1347
       kernel_init_freeable+0x3d9/0x570 init/main.c:1579
       kernel_init+0x1d/0x1d0 init/main.c:1469
       ret_from_fork+0x3fc/0x770 arch/x86/kernel/process.c:148
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #4 (&q->elevator_lock){+.+.}-{4:4}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5871
       __mutex_lock_common kernel/locking/mutex.c:602 [inline]
       __mutex_lock+0x182/0xe80 kernel/locking/mutex.c:747
       elv_update_nr_hw_queues+0x87/0x2a0 block/elevator.c:699
       __blk_mq_update_nr_hw_queues block/blk-mq.c:5024 [inline]
       blk_mq_update_nr_hw_queues+0xd54/0x14c0 block/blk-mq.c:5045
       nbd_start_device+0x16c/0xac0 drivers/block/nbd.c:1476
       nbd_genl_connect+0x1250/0x1930 drivers/block/nbd.c:2201
       genl_family_rcv_msg_doit+0x212/0x300 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:2534
       genl_rcv+0x28/0x40 net/netlink/genetlink.c:1219
       netlink_unicast_kernel net/netlink/af_netlink.c:1313 [inline]
       netlink_unicast+0x75b/0x8d0 net/netlink/af_netlink.c:1339
       netlink_sendmsg+0x805/0xb30 net/netlink/af_netlink.c:1883
       sock_sendmsg_nosec net/socket.c:714 [inline]
       __sock_sendmsg+0x219/0x270 net/socket.c:729
       ____sys_sendmsg+0x505/0x830 net/socket.c:2614
       ___sys_sendmsg+0x21f/0x2a0 net/socket.c:2668
       __sys_sendmsg net/socket.c:2700 [inline]
       __do_sys_sendmsg net/socket.c:2705 [inline]
       __se_sys_sendmsg net/socket.c:2703 [inline]
       __x64_sys_sendmsg+0x19b/0x260 net/socket.c:2703
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #3 (&q->q_usage_counter(io)#49){++++}-{0:0}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5871
       blk_alloc_queue+0x538/0x620 block/blk-core.c:461
       blk_mq_alloc_queue block/blk-mq.c:4398 [inline]
       __blk_mq_alloc_disk+0x162/0x340 block/blk-mq.c:4445
       nbd_dev_add+0x476/0xb00 drivers/block/nbd.c:1933
       nbd_init+0x21a/0x2d0 drivers/block/nbd.c:2670
       do_one_initcall+0x233/0x820 init/main.c:1269
       do_initcall_level+0x137/0x1f0 init/main.c:1331
       do_initcalls+0x69/0xd0 init/main.c:1347
       kernel_init_freeable+0x3d9/0x570 init/main.c:1579
       kernel_init+0x1d/0x1d0 init/main.c:1469
       ret_from_fork+0x3fc/0x770 arch/x86/kernel/process.c:148
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #2 (fs_reclaim){+.+.}-{0:0}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5871
       __fs_reclaim_acquire mm/page_alloc.c:4231 [inline]
       fs_reclaim_acquire+0x72/0x100 mm/page_alloc.c:4245
       might_alloc include/linux/sched/mm.h:318 [inline]
       slab_pre_alloc_hook mm/slub.c:4131 [inline]
       slab_alloc_node mm/slub.c:4209 [inline]
       kmem_cache_alloc_node_noprof+0x47/0x3c0 mm/slub.c:4281
       __alloc_skb+0x112/0x2d0 net/core/skbuff.c:660
       alloc_skb_fclone include/linux/skbuff.h:1386 [inline]
       tcp_stream_alloc_skb+0x3d/0x340 net/ipv4/tcp.c:892
       tcp_sendmsg_locked+0x1f46/0x5630 net/ipv4/tcp.c:1198
       tcp_sendmsg+0x2f/0x50 net/ipv4/tcp.c:1394
       sock_sendmsg_nosec net/socket.c:714 [inline]
       __sock_sendmsg+0x19c/0x270 net/socket.c:729
       sock_write_iter+0x258/0x330 net/socket.c:1179
       new_sync_write fs/read_write.c:593 [inline]
       vfs_write+0x548/0xa90 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/0x3b0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (sk_lock-AF_INET){+.+.}-{0:0}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5871
       lock_sock_nested+0x48/0x100 net/core/sock.c:3727
       lock_sock include/net/sock.h:1667 [inline]
       inet_shutdown+0x6a/0x390 net/ipv4/af_inet.c:905
       nbd_mark_nsock_dead+0x2e9/0x560 drivers/block/nbd.c:318
       recv_work+0x2138/0x24f0 drivers/block/nbd.c:1018
       process_one_work kernel/workqueue.c:3239 [inline]
       process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3322
       worker_thread+0x8a0/0xda0 kernel/workqueue.c:3403
       kthread+0x70e/0x8a0 kernel/kthread.c:463
       ret_from_fork+0x3fc/0x770 arch/x86/kernel/process.c:148
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #0 (&nsock->tx_lock){+.+.}-{4:4}:
       check_prev_add kernel/locking/lockdep.c:3168 [inline]
       check_prevs_add kernel/locking/lockdep.c:3287 [inline]
       validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3911
       __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5240
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5871
       __mutex_lock_common kernel/locking/mutex.c:602 [inline]
       __mutex_lock+0x182/0xe80 kernel/locking/mutex.c:747
       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:2118
       __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:2356
       blk_mq_dispatch_list+0xd0c/0xe00 include/linux/spinlock.h:-1
       blk_mq_flush_plug_list+0x469/0x550 block/blk-mq.c:2965
       __blk_flush_plug+0x3d3/0x4b0 block/blk-core.c:1220
       blk_finish_plug block/blk-core.c:1247 [inline]
       __submit_bio+0x2d3/0x5a0 block/blk-core.c:649
       __submit_bio_noacct_mq block/blk-core.c:722 [inline]
       submit_bio_noacct_nocheck+0x4ab/0xb50 block/blk-core.c:751
       submit_bh fs/buffer.c:2829 [inline]
       block_read_full_folio+0x7b7/0x830 fs/buffer.c:2461
       filemap_read_folio+0x117/0x380 mm/filemap.c:2413
       do_read_cache_folio+0x350/0x590 mm/filemap.c:3957
       read_mapping_folio include/linux/pagemap.h:972 [inline]
       read_part_sector+0xb6/0x2b0 block/partitions/core.c:722
       adfspart_check_ICS+0xa4/0xa50 block/partitions/acorn.c:360
       check_partition block/partitions/core.c:141 [inline]
       blk_add_partitions block/partitions/core.c:589 [inline]
       bdev_disk_changed+0x75c/0x14b0 block/partitions/core.c:693
       blkdev_get_whole+0x380/0x510 block/bdev.c:748
       bdev_open+0x31e/0xd30 block/bdev.c:957
       blkdev_open+0x3a8/0x510 block/fops.c:676
       do_dentry_open+0xdf0/0x1970 fs/open.c:964
       vfs_open+0x3b/0x340 fs/open.c:1094
       do_open fs/namei.c:3887 [inline]
       path_openat+0x2ee5/0x3830 fs/namei.c:4046
       do_filp_open+0x1fa/0x410 fs/namei.c:4073
       do_sys_openat2+0x121/0x1c0 fs/open.c:1434
       do_sys_open fs/open.c:1449 [inline]
       __do_sys_openat fs/open.c:1465 [inline]
       __se_sys_openat fs/open.c:1460 [inline]
       __x64_sys_openat+0x138/0x170 fs/open.c:1460
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0x3b0 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:
  &nsock->tx_lock --> set->srcu --> &cmd->lock

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&cmd->lock);
                               lock(set->srcu);
                               lock(&cmd->lock);
  lock(&nsock->tx_lock);

 *** DEADLOCK ***

3 locks held by udevd/6083:
 #0: ffff888024ed8358 (&disk->open_mutex){+.+.}-{4:4}, at: bdev_open+0xe0/0xd30 block/bdev.c:945
 #1: ffff888024d36f90 (set->srcu){.+.+}-{0:0}, at: srcu_lock_acquire include/linux/srcu.h:161 [inline]
 #1: ffff888024d36f90 (set->srcu){.+.+}-{0:0}, at: srcu_read_lock include/linux/srcu.h:253 [inline]
 #1: ffff888024d36f90 (set->srcu){.+.+}-{0:0}, at: blk_mq_run_hw_queue+0x31f/0x4f0 block/blk-mq.c:2356
 #2: ffff8880597ee178 (&cmd->lock){+.+.}-{4:4}, at: nbd_queue_rq+0xc8/0xf10 drivers/block/nbd.c:1196

stack backtrace:
CPU: 0 UID: 0 PID: 6083 Comm: udevd Not tainted 6.16.0-rc4-next-20250704-syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 print_circular_bug+0x2ee/0x310 kernel/locking/lockdep.c:2046
 check_noncircular+0x134/0x160 kernel/locking/lockdep.c:2178
 check_prev_add kernel/locking/lockdep.c:3168 [inline]
 check_prevs_add kernel/locking/lockdep.c:3287 [inline]
 validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3911
 __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5240
 lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5871
 __mutex_lock_common kernel/locking/mutex.c:602 [inline]
 __mutex_lock+0x182/0xe80 kernel/locking/mutex.c:747
 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:2118
 __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:2356
 blk_mq_dispatch_list+0xd0c/0xe00 include/linux/spinlock.h:-1
 blk_mq_flush_plug_list+0x469/0x550 block/blk-mq.c:2965
 __blk_flush_plug+0x3d3/0x4b0 block/blk-core.c:1220
 blk_finish_plug block/blk-core.c:1247 [inline]
 __submit_bio+0x2d3/0x5a0 block/blk-core.c:649
 __submit_bio_noacct_mq block/blk-core.c:722 [inline]
 submit_bio_noacct_nocheck+0x4ab/0xb50 block/blk-core.c:751
 submit_bh fs/buffer.c:2829 [inline]
 block_read_full_folio+0x7b7/0x830 fs/buffer.c:2461
 filemap_read_folio+0x117/0x380 mm/filemap.c:2413
 do_read_cache_folio+0x350/0x590 mm/filemap.c:3957
 read_mapping_folio include/linux/pagemap.h:972 [inline]
 read_part_sector+0xb6/0x2b0 block/partitions/core.c:722
 adfspart_check_ICS+0xa4/0xa50 block/partitions/acorn.c:360
 check_partition block/partitions/core.c:141 [inline]
 blk_add_partitions block/partitions/core.c:589 [inline]
 bdev_disk_changed+0x75c/0x14b0 block/partitions/core.c:693
 blkdev_get_whole+0x380/0x510 block/bdev.c:748
 bdev_open+0x31e/0xd30 block/bdev.c:957
 blkdev_open+0x3a8/0x510 block/fops.c:676
 do_dentry_open+0xdf0/0x1970 fs/open.c:964
 vfs_open+0x3b/0x340 fs/open.c:1094
 do_open fs/namei.c:3887 [inline]
 path_openat+0x2ee5/0x3830 fs/namei.c:4046
 do_filp_open+0x1fa/0x410 fs/namei.c:4073
 do_sys_openat2+0x121/0x1c0 fs/open.c:1434
 do_sys_open fs/open.c:1449 [inline]
 __do_sys_openat fs/open.c:1465 [inline]
 __se_sys_openat fs/open.c:1460 [inline]
 __x64_sys_openat+0x138/0x170 fs/open.c:1460
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f674caa7407
Code: 48 89 fa 4c 89 df e8 38 aa 00 00 8b 93 08 03 00 00 59 5e 48 83 f8 fc 74 1a 5b c3 0f 1f 84 00 00 00 00 00 48 8b 44 24 10 0f 05 <5b> c3 0f 1f 80 00 00 00 00 83 e2 39 83 fa 08 75 de e8 23 ff ff ff
RSP: 002b:00007fff79271070 EFLAGS: 00000202 ORIG_RAX: 0000000000000101
RAX: ffffffffffffffda RBX: 00007f674d25e880 RCX: 00007f674caa7407
RDX: 00000000000a0800 RSI: 000055ad17c52fe0 RDI: ffffffffffffff9c
RBP: 000055ad17c52910 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000202 R12: 000055ad17c53000
R13: 000055ad17c6a430 R14: 0000000000000000 R15: 000055ad17c53000
 </TASK>
block nbd0: Dead connection, failed to find a fallback
block nbd0: shutting down sockets
I/O error, dev nbd0, sector 0 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
Buffer I/O error on dev nbd0, logical block 0, async page read
I/O error, dev nbd0, sector 0 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
Buffer I/O error on dev nbd0, logical block 0, async page read
I/O error, dev nbd0, sector 0 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
Buffer I/O error on dev nbd0, logical block 0, async page read
I/O error, dev nbd0, sector 0 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
Buffer I/O error on dev nbd0, logical block 0, async page read
I/O error, dev nbd0, sector 0 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
Buffer I/O error on dev nbd0, logical block 0, async page read
I/O error, dev nbd0, sector 0 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
Buffer I/O error on dev nbd0, logical block 0, async page read
I/O error, dev nbd0, sector 0 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
Buffer I/O error on dev nbd0, logical block 0, async page read
I/O error, dev nbd0, sector 0 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
Buffer I/O error on dev nbd0, logical block 0, async page read
ldm_validate_partition_table(): Disk read failed.
I/O error, dev nbd0, sector 0 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
Buffer I/O error on dev nbd0, logical block 0, async page read
I/O error, dev nbd0, sector 0 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
Buffer I/O error on dev nbd0, logical block 0, async page read
Dev nbd0: unable to read RDB block 0
 nbd0: unable to read partition table
ldm_validate_partition_table(): Disk read failed.
Dev nbd0: unable to read RDB block 0
 nbd0: unable to read partition table