syzbot

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
udevd/5967 is trying to acquire lock:
ffff888073b90070 (&nsock->tx_lock){+.+.}-{4:4}, at: nbd_handle_cmd drivers/block/nbd.c:1140 [inline]
ffff888073b90070 (&nsock->tx_lock){+.+.}-{4:4}, at: nbd_queue_rq+0x423/0x12d0 drivers/block/nbd.c:1204

but task is already holding lock:
ffff88807d35e178 (&cmd->lock){+.+.}-{4:4}, at: nbd_queue_rq+0xbd/0x12d0 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}:
       __mutex_lock_common kernel/locking/mutex.c:598 [inline]
       __mutex_lock+0x193/0x1060 kernel/locking/mutex.c:760
       nbd_queue_rq+0xbd/0x12d0 drivers/block/nbd.c:1196
       blk_mq_dispatch_rq_list+0x413/0x1e20 block/blk-mq.c:2120
       __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+0xcb7/0x15f0 block/blk-mq-sched.c:307
       blk_mq_sched_dispatch_requests+0xd8/0x1b0 block/blk-mq-sched.c:329
       blk_mq_run_hw_queue+0x239/0x670 block/blk-mq.c:2358
       blk_mq_dispatch_list+0x514/0x1310 block/blk-mq.c:2919
       blk_mq_flush_plug_list block/blk-mq.c:2967 [inline]
       blk_mq_flush_plug_list+0x130/0x600 block/blk-mq.c:2939
       __blk_flush_plug+0x2c4/0x4b0 block/blk-core.c:1220
       blk_finish_plug block/blk-core.c:1247 [inline]
       blk_finish_plug block/blk-core.c:1244 [inline]
       __submit_bio+0x545/0x690 block/blk-core.c:649
       __submit_bio_noacct_mq block/blk-core.c:722 [inline]
       submit_bio_noacct_nocheck+0x660/0xd30 block/blk-core.c:751
       submit_bio_noacct+0xc20/0x1ed0 block/blk-core.c:874
       submit_bh fs/buffer.c:2829 [inline]
       block_read_full_folio+0x4db/0x850 fs/buffer.c:2461
       filemap_read_folio+0xc5/0x2a0 mm/filemap.c:2413
       do_read_cache_folio+0x263/0x5c0 mm/filemap.c:3957
       read_mapping_folio include/linux/pagemap.h:991 [inline]
       read_part_sector+0xd4/0x370 block/partitions/core.c:722
       adfspart_check_ICS+0x93/0x940 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+0x723/0x1520 block/partitions/core.c:693
       blkdev_get_whole+0x187/0x290 block/bdev.c:748
       bdev_open+0x2c7/0xe40 block/bdev.c:957
       blkdev_open+0x34e/0x4f0 block/fops.c:694
       do_dentry_open+0x97f/0x1530 fs/open.c:965
       vfs_open+0x82/0x3f0 fs/open.c:1095
       do_open fs/namei.c:3887 [inline]
       path_openat+0x1de4/0x2cb0 fs/namei.c:4046
       do_filp_open+0x20b/0x470 fs/namei.c:4073
       do_sys_openat2+0x11b/0x1d0 fs/open.c:1435
       do_sys_open fs/open.c:1450 [inline]
       __do_sys_openat fs/open.c:1466 [inline]
       __se_sys_openat fs/open.c:1461 [inline]
       __x64_sys_openat+0x174/0x210 fs/open.c:1461
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xcd/0x4e0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #5 (set->srcu){.+.+}-{0:0}:
       srcu_lock_sync include/linux/srcu.h:173 [inline]
       __synchronize_srcu+0xa1/0x290 kernel/rcu/srcutree.c:1429
       blk_mq_wait_quiesce_done block/blk-mq.c:283 [inline]
       blk_mq_wait_quiesce_done block/blk-mq.c:280 [inline]
       blk_mq_quiesce_queue block/blk-mq.c:303 [inline]
       blk_mq_quiesce_queue+0x149/0x1b0 block/blk-mq.c:298
       elevator_switch+0x17d/0x810 block/elevator.c:588
       elevator_change+0x391/0x580 block/elevator.c:690
       elevator_set_default+0x2e9/0x380 block/elevator.c:766
       blk_register_queue+0x384/0x4e0 block/blk-sysfs.c:904
       __add_disk+0x74a/0xf00 block/genhd.c:528
       add_disk_fwnode+0x13f/0x5d0 block/genhd.c:597
       add_disk include/linux/blkdev.h:774 [inline]
       nbd_dev_add+0x783/0xbb0 drivers/block/nbd.c:1973
       nbd_init+0x181/0x320 drivers/block/nbd.c:2680
       do_one_initcall+0x120/0x6e0 init/main.c:1269
       do_initcall_level init/main.c:1331 [inline]
       do_initcalls init/main.c:1347 [inline]
       do_basic_setup init/main.c:1366 [inline]
       kernel_init_freeable+0x5c2/0x910 init/main.c:1579
       kernel_init+0x1c/0x2b0 init/main.c:1469
       ret_from_fork+0x56a/0x730 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}:
       __mutex_lock_common kernel/locking/mutex.c:598 [inline]
       __mutex_lock+0x193/0x1060 kernel/locking/mutex.c:760
       elevator_change+0x17d/0x580 block/elevator.c:688
       elevator_set_none+0xaa/0x120 block/elevator.c:781
       blk_mq_elv_switch_none block/blk-mq.c:5023 [inline]
       __blk_mq_update_nr_hw_queues+0x4bd/0x1200 block/blk-mq.c:5066
       blk_mq_update_nr_hw_queues+0x3b/0x60 block/blk-mq.c:5124
       nbd_start_device+0x1b0/0xd70 drivers/block/nbd.c:1478
       nbd_genl_connect+0x134b/0x1c60 drivers/block/nbd.c:2228
       genl_family_rcv_msg_doit+0x206/0x2f0 net/netlink/genetlink.c:1115
       genl_family_rcv_msg net/netlink/genetlink.c:1195 [inline]
       genl_rcv_msg+0x55c/0x800 net/netlink/genetlink.c:1210
       netlink_rcv_skb+0x158/0x420 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+0x5a7/0x870 net/netlink/af_netlink.c:1346
       netlink_sendmsg+0x8d1/0xdd0 net/netlink/af_netlink.c:1896
       sock_sendmsg_nosec net/socket.c:714 [inline]
       __sock_sendmsg net/socket.c:729 [inline]
       ____sys_sendmsg+0xa95/0xc70 net/socket.c:2614
       ___sys_sendmsg+0x134/0x1d0 net/socket.c:2668
       __sys_sendmsg+0x16d/0x220 net/socket.c:2700
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xcd/0x4e0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #3 (&q->q_usage_counter(io)#49){++++}-{0:0}:
       blk_alloc_queue+0x619/0x760 block/blk-core.c:461
       blk_mq_alloc_queue+0x172/0x280 block/blk-mq.c:4400
       __blk_mq_alloc_disk+0x29/0x120 block/blk-mq.c:4447
       nbd_dev_add+0x492/0xbb0 drivers/block/nbd.c:1943
       nbd_init+0x181/0x320 drivers/block/nbd.c:2680
       do_one_initcall+0x120/0x6e0 init/main.c:1269
       do_initcall_level init/main.c:1331 [inline]
       do_initcalls init/main.c:1347 [inline]
       do_basic_setup init/main.c:1366 [inline]
       kernel_init_freeable+0x5c2/0x910 init/main.c:1579
       kernel_init+0x1c/0x2b0 init/main.c:1469
       ret_from_fork+0x56a/0x730 arch/x86/kernel/process.c:148
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #2 (fs_reclaim){+.+.}-{0:0}:
       __fs_reclaim_acquire mm/page_alloc.c:4234 [inline]
       fs_reclaim_acquire+0x102/0x150 mm/page_alloc.c:4248
       might_alloc include/linux/sched/mm.h:318 [inline]
       slab_pre_alloc_hook mm/slub.c:4142 [inline]
       slab_alloc_node mm/slub.c:4220 [inline]
       __kmalloc_cache_noprof+0x50/0x3e0 mm/slub.c:4402
       kmalloc_noprof include/linux/slab.h:905 [inline]
       kzalloc_noprof include/linux/slab.h:1039 [inline]
       virtio_transport_do_socket_init+0x4a/0x350 net/vmw_vsock/virtio_transport_common.c:910
       vsock_assign_transport+0x63d/0x900 net/vmw_vsock/af_vsock.c:537
       vsock_connect+0x201/0xee0 net/vmw_vsock/af_vsock.c:1583
       __sys_connect_file+0x13e/0x1a0 net/socket.c:2086
       __sys_connect+0x13b/0x160 net/socket.c:2105
       __do_sys_connect net/socket.c:2111 [inline]
       __se_sys_connect net/socket.c:2108 [inline]
       __x64_sys_connect+0x72/0xb0 net/socket.c:2108
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xcd/0x4e0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (sk_lock-AF_VSOCK){+.+.}-{0:0}:
       lock_sock_nested+0x41/0xf0 net/core/sock.c:3711
       lock_sock include/net/sock.h:1669 [inline]
       vsock_shutdown+0x61/0x2d0 net/vmw_vsock/af_vsock.c:1103
       nbd_mark_nsock_dead+0xae/0x5d0 drivers/block/nbd.c:318
       recv_work+0x671/0xa80 drivers/block/nbd.c:1018
       process_one_work+0x9cc/0x1b70 kernel/workqueue.c:3236
       process_scheduled_works kernel/workqueue.c:3319 [inline]
       worker_thread+0x6c8/0xf10 kernel/workqueue.c:3400
       kthread+0x3c2/0x780 kernel/kthread.c:463
       ret_from_fork+0x56a/0x730 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:3165 [inline]
       check_prevs_add kernel/locking/lockdep.c:3284 [inline]
       validate_chain kernel/locking/lockdep.c:3908 [inline]
       __lock_acquire+0x12a6/0x1ce0 kernel/locking/lockdep.c:5237
       lock_acquire kernel/locking/lockdep.c:5868 [inline]
       lock_acquire+0x179/0x350 kernel/locking/lockdep.c:5825
       __mutex_lock_common kernel/locking/mutex.c:598 [inline]
       __mutex_lock+0x193/0x1060 kernel/locking/mutex.c:760
       nbd_handle_cmd drivers/block/nbd.c:1140 [inline]
       nbd_queue_rq+0x423/0x12d0 drivers/block/nbd.c:1204
       blk_mq_dispatch_rq_list+0x413/0x1e20 block/blk-mq.c:2120
       __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+0xcb7/0x15f0 block/blk-mq-sched.c:307
       blk_mq_sched_dispatch_requests+0xd8/0x1b0 block/blk-mq-sched.c:329
       blk_mq_run_hw_queue+0x239/0x670 block/blk-mq.c:2358
       blk_mq_dispatch_list+0x514/0x1310 block/blk-mq.c:2919
       blk_mq_flush_plug_list block/blk-mq.c:2967 [inline]
       blk_mq_flush_plug_list+0x130/0x600 block/blk-mq.c:2939
       __blk_flush_plug+0x2c4/0x4b0 block/blk-core.c:1220
       blk_finish_plug block/blk-core.c:1247 [inline]
       blk_finish_plug block/blk-core.c:1244 [inline]
       __submit_bio+0x545/0x690 block/blk-core.c:649
       __submit_bio_noacct_mq block/blk-core.c:722 [inline]
       submit_bio_noacct_nocheck+0x660/0xd30 block/blk-core.c:751
       submit_bio_noacct+0xc20/0x1ed0 block/blk-core.c:874
       submit_bh fs/buffer.c:2829 [inline]
       block_read_full_folio+0x4db/0x850 fs/buffer.c:2461
       filemap_read_folio+0xc5/0x2a0 mm/filemap.c:2413
       do_read_cache_folio+0x263/0x5c0 mm/filemap.c:3957
       read_mapping_folio include/linux/pagemap.h:991 [inline]
       read_part_sector+0xd4/0x370 block/partitions/core.c:722
       adfspart_check_ICS+0x93/0x940 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+0x723/0x1520 block/partitions/core.c:693
       blkdev_get_whole+0x187/0x290 block/bdev.c:748
       bdev_open+0x2c7/0xe40 block/bdev.c:957
       blkdev_open+0x34e/0x4f0 block/fops.c:694
       do_dentry_open+0x97f/0x1530 fs/open.c:965
       vfs_open+0x82/0x3f0 fs/open.c:1095
       do_open fs/namei.c:3887 [inline]
       path_openat+0x1de4/0x2cb0 fs/namei.c:4046
       do_filp_open+0x20b/0x470 fs/namei.c:4073
       do_sys_openat2+0x11b/0x1d0 fs/open.c:1435
       do_sys_open fs/open.c:1450 [inline]
       __do_sys_openat fs/open.c:1466 [inline]
       __se_sys_openat fs/open.c:1461 [inline]
       __x64_sys_openat+0x174/0x210 fs/open.c:1461
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xcd/0x4e0 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/5967:
 #0: ffff888143767358 (&disk->open_mutex){+.+.}-{4:4}, at: bdev_open+0x41a/0xe40 block/bdev.c:945
 #1: ffff8881433cdd10 (set->srcu){.+.+}-{0:0}, at: srcu_lock_acquire include/linux/srcu.h:161 [inline]
 #1: ffff8881433cdd10 (set->srcu){.+.+}-{0:0}, at: srcu_read_lock include/linux/srcu.h:253 [inline]
 #1: ffff8881433cdd10 (set->srcu){.+.+}-{0:0}, at: blk_mq_run_hw_queue+0x22b/0x670 block/blk-mq.c:2358
 #2: ffff88807d35e178 (&cmd->lock){+.+.}-{4:4}, at: nbd_queue_rq+0xbd/0x12d0 drivers/block/nbd.c:1196

stack backtrace:
CPU: 0 UID: 0 PID: 5967 Comm: udevd Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
 print_circular_bug+0x275/0x350 kernel/locking/lockdep.c:2043
 check_noncircular+0x14c/0x170 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+0x12a6/0x1ce0 kernel/locking/lockdep.c:5237
 lock_acquire kernel/locking/lockdep.c:5868 [inline]
 lock_acquire+0x179/0x350 kernel/locking/lockdep.c:5825
 __mutex_lock_common kernel/locking/mutex.c:598 [inline]
 __mutex_lock+0x193/0x1060 kernel/locking/mutex.c:760
 nbd_handle_cmd drivers/block/nbd.c:1140 [inline]
 nbd_queue_rq+0x423/0x12d0 drivers/block/nbd.c:1204
 blk_mq_dispatch_rq_list+0x413/0x1e20 block/blk-mq.c:2120
 __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+0xcb7/0x15f0 block/blk-mq-sched.c:307
 blk_mq_sched_dispatch_requests+0xd8/0x1b0 block/blk-mq-sched.c:329
 blk_mq_run_hw_queue+0x239/0x670 block/blk-mq.c:2358
 blk_mq_dispatch_list+0x514/0x1310 block/blk-mq.c:2919
 blk_mq_flush_plug_list block/blk-mq.c:2967 [inline]
 blk_mq_flush_plug_list+0x130/0x600 block/blk-mq.c:2939
 __blk_flush_plug+0x2c4/0x4b0 block/blk-core.c:1220
 blk_finish_plug block/blk-core.c:1247 [inline]
 blk_finish_plug block/blk-core.c:1244 [inline]
 __submit_bio+0x545/0x690 block/blk-core.c:649
 __submit_bio_noacct_mq block/blk-core.c:722 [inline]
 submit_bio_noacct_nocheck+0x660/0xd30 block/blk-core.c:751
 submit_bio_noacct+0xc20/0x1ed0 block/blk-core.c:874
 submit_bh fs/buffer.c:2829 [inline]
 block_read_full_folio+0x4db/0x850 fs/buffer.c:2461
 filemap_read_folio+0xc5/0x2a0 mm/filemap.c:2413
 do_read_cache_folio+0x263/0x5c0 mm/filemap.c:3957
 read_mapping_folio include/linux/pagemap.h:991 [inline]
 read_part_sector+0xd4/0x370 block/partitions/core.c:722
 adfspart_check_ICS+0x93/0x940 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+0x723/0x1520 block/partitions/core.c:693
 blkdev_get_whole+0x187/0x290 block/bdev.c:748
 bdev_open+0x2c7/0xe40 block/bdev.c:957
 blkdev_open+0x34e/0x4f0 block/fops.c:694
 do_dentry_open+0x97f/0x1530 fs/open.c:965
 vfs_open+0x82/0x3f0 fs/open.c:1095
 do_open fs/namei.c:3887 [inline]
 path_openat+0x1de4/0x2cb0 fs/namei.c:4046
 do_filp_open+0x20b/0x470 fs/namei.c:4073
 do_sys_openat2+0x11b/0x1d0 fs/open.c:1435
 do_sys_open fs/open.c:1450 [inline]
 __do_sys_openat fs/open.c:1466 [inline]
 __se_sys_openat fs/open.c:1461 [inline]
 __x64_sys_openat+0x174/0x210 fs/open.c:1461
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xcd/0x4e0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f7378aa7407
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:00007ffefea3ae00 EFLAGS: 00000202 ORIG_RAX: 0000000000000101
RAX: ffffffffffffffda RBX: 00007f737918e880 RCX: 00007f7378aa7407
RDX: 00000000000a0800 RSI: 000055a7d4a2f700 RDI: ffffffffffffff9c
RBP: 000055a7d4a2c2c0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000202 R12: 000055a7d4f32e80
R13: 000055a7d4c678d0 R14: 0000000000000000 R15: 000055a7d4f32e80
 </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 2
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 2
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 2
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 2
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 2
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 2
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 2
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 2
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 2
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 2
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