syzbot

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Tainted: G             L     
------------------------------------------------------
udevd/5819 is trying to acquire lock:
ffff8880784a7670 (&nsock->tx_lock){+.+.}-{4:4}, at: nbd_handle_cmd drivers/block/nbd.c:1143 [inline]
ffff8880784a7670 (&nsock->tx_lock){+.+.}-{4:4}, at: nbd_queue_rq+0x423/0x12d0 drivers/block/nbd.c:1207

but task is already holding lock:
ffff888026610180 (&cmd->lock){+.+.}-{4:4}, at: nbd_queue_rq+0xbd/0x12d0 drivers/block/nbd.c:1199

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:614 [inline]
       __mutex_lock+0x1aa/0x1ca0 kernel/locking/mutex.c:776
       nbd_queue_rq+0xbd/0x12d0 drivers/block/nbd.c:1199
       blk_mq_dispatch_rq_list+0x416/0x1e20 block/blk-mq.c:2138
       __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+0xcbd/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:2376
       blk_mq_dispatch_list+0x514/0x1300 block/blk-mq.c:2939
       blk_mq_flush_plug_list block/blk-mq.c:2987 [inline]
       blk_mq_flush_plug_list+0x130/0x600 block/blk-mq.c:2959
       __blk_flush_plug+0x2c4/0x4b0 block/blk-core.c:1225
       blk_finish_plug block/blk-core.c:1252 [inline]
       blk_finish_plug block/blk-core.c:1249 [inline]
       __submit_bio+0x542/0x690 block/blk-core.c:651
       __submit_bio_noacct_mq block/blk-core.c:724 [inline]
       submit_bio_noacct_nocheck+0x53d/0xbe0 block/blk-core.c:755
       submit_bio_noacct+0x5bd/0x1f40 block/blk-core.c:879
       submit_bh fs/buffer.c:2829 [inline]
       block_read_full_folio+0x4db/0x850 fs/buffer.c:2461
       filemap_read_folio+0xc8/0x2a0 mm/filemap.c:2496
       do_read_cache_folio+0x266/0x5c0 mm/filemap.c:4096
       read_mapping_folio include/linux/pagemap.h:1017 [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:765
       bdev_open+0x2c7/0xe40 block/bdev.c:974
       blkdev_open+0x34e/0x4f0 block/fops.c:698
       do_dentry_open+0x748/0x1590 fs/open.c:962
       vfs_open+0x82/0x3f0 fs/open.c:1094
       do_open fs/namei.c:4628 [inline]
       path_openat+0x2078/0x3140 fs/namei.c:4787
       do_filp_open+0x20b/0x470 fs/namei.c:4814
       do_sys_openat2+0x121/0x290 fs/open.c:1430
       do_sys_open fs/open.c:1436 [inline]
       __do_sys_openat fs/open.c:1452 [inline]
       __se_sys_openat fs/open.c:1447 [inline]
       __x64_sys_openat+0x174/0x210 fs/open.c:1447
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xcd/0xf80 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:197 [inline]
       __synchronize_srcu+0xa2/0x250 kernel/rcu/srcutree.c:1503
       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+0x149/0x1b0 block/blk-mq.c:299
       elevator_switch+0x17d/0x7f0 block/elevator.c:576
       elevator_change+0x38b/0x570 block/elevator.c:680
       elevator_set_default+0x2d2/0x390 block/elevator.c:753
       blk_register_queue+0x384/0x4e0 block/blk-sysfs.c:932
       __add_disk+0x74a/0xf00 block/genhd.c:528
       add_disk_fwnode+0x13f/0x5d0 block/genhd.c:597
       add_disk include/linux/blkdev.h:785 [inline]
       nbd_dev_add+0x783/0xbb0 drivers/block/nbd.c:1984
       nbd_init+0x181/0x320 drivers/block/nbd.c:2692
       do_one_initcall+0x123/0x680 init/main.c:1378
       do_initcall_level init/main.c:1440 [inline]
       do_initcalls init/main.c:1456 [inline]
       do_basic_setup init/main.c:1475 [inline]
       kernel_init_freeable+0x5c8/0x920 init/main.c:1688
       kernel_init+0x1c/0x2b0 init/main.c:1578
       ret_from_fork+0x983/0xb10 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246

-> #4 (&q->elevator_lock){+.+.}-{4:4}:
       __mutex_lock_common kernel/locking/mutex.c:614 [inline]
       __mutex_lock+0x1aa/0x1ca0 kernel/locking/mutex.c:776
       elevator_change+0x1ed/0x570 block/elevator.c:678
       elv_iosched_store+0x3e8/0x4a0 block/elevator.c:811
       queue_attr_store+0x26b/0x310 block/blk-sysfs.c:859
       sysfs_kf_write+0xf2/0x150 fs/sysfs/file.c:142
       kernfs_fop_write_iter+0x3af/0x570 fs/kernfs/file.c:352
       iter_file_splice_write+0xa24/0x12b0 fs/splice.c:738
       do_splice_from fs/splice.c:938 [inline]
       direct_splice_actor+0x192/0x6c0 fs/splice.c:1161
       splice_direct_to_actor+0x345/0xa30 fs/splice.c:1105
       do_splice_direct_actor fs/splice.c:1204 [inline]
       do_splice_direct+0x174/0x240 fs/splice.c:1230
       do_sendfile+0xb06/0xe50 fs/read_write.c:1370
       __do_sys_sendfile64 fs/read_write.c:1431 [inline]
       __se_sys_sendfile64 fs/read_write.c:1417 [inline]
       __x64_sys_sendfile64+0x1d8/0x220 fs/read_write.c:1417
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xcd/0xf80 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #3 (&q->q_usage_counter(io)#66){++++}-{0:0}:
       blk_alloc_queue+0x610/0x750 block/blk-core.c:461
       blk_mq_alloc_queue+0x172/0x280 block/blk-mq.c:4415
       __blk_mq_alloc_disk+0x29/0x120 block/blk-mq.c:4462
       null_add_dev+0xf2e/0x1eb0 drivers/block/null_blk/main.c:1999
       null_create_dev drivers/block/null_blk/main.c:2097 [inline]
       null_init+0x2c9/0x610 drivers/block/null_blk/main.c:2169
       do_one_initcall+0x123/0x680 init/main.c:1378
       do_initcall_level init/main.c:1440 [inline]
       do_initcalls init/main.c:1456 [inline]
       do_basic_setup init/main.c:1475 [inline]
       kernel_init_freeable+0x5c8/0x920 init/main.c:1688
       kernel_init+0x1c/0x2b0 init/main.c:1578
       ret_from_fork+0x983/0xb10 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246

-> #2 (fs_reclaim){+.+.}-{0:0}:
       __fs_reclaim_acquire mm/page_alloc.c:4301 [inline]
       fs_reclaim_acquire+0x102/0x150 mm/page_alloc.c:4315
       might_alloc include/linux/sched/mm.h:317 [inline]
       slab_pre_alloc_hook mm/slub.c:4904 [inline]
       slab_alloc_node mm/slub.c:5239 [inline]
       kmem_cache_alloc_node_noprof+0x5e/0x800 mm/slub.c:5315
       __alloc_skb+0x156/0x410 net/core/skbuff.c:679
       alloc_skb_fclone include/linux/skbuff.h:1433 [inline]
       tcp_stream_alloc_skb+0x34/0x670 net/ipv4/tcp.c:910
       tcp_sendmsg_locked+0x12de/0x42a0 net/ipv4/tcp.c:1217
       tcp_sendmsg+0x2e/0x50 net/ipv4/tcp.c:1412
       inet_sendmsg+0xb9/0x140 net/ipv4/af_inet.c:859
       sock_sendmsg_nosec net/socket.c:727 [inline]
       __sock_sendmsg net/socket.c:742 [inline]
       sock_write_iter+0x509/0x610 net/socket.c:1195
       new_sync_write fs/read_write.c:593 [inline]
       vfs_write+0x7d3/0x11d0 fs/read_write.c:686
       ksys_write+0x1f8/0x250 fs/read_write.c:738
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xcd/0xf80 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (sk_lock-AF_INET){+.+.}-{0:0}:
       lock_sock_nested+0x41/0xf0 net/core/sock.c:3780
       lock_sock include/net/sock.h:1700 [inline]
       inet_shutdown+0x67/0x440 net/ipv4/af_inet.c:913
       nbd_mark_nsock_dead+0xae/0x5d0 drivers/block/nbd.c:318
       recv_work+0x66b/0xa70 drivers/block/nbd.c:1021
       process_one_work+0x9ba/0x1b20 kernel/workqueue.c:3257
       process_scheduled_works kernel/workqueue.c:3340 [inline]
       worker_thread+0x6c8/0xf10 kernel/workqueue.c:3421
       kthread+0x3c5/0x780 kernel/kthread.c:463
       ret_from_fork+0x983/0xb10 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246

-> #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+0x1669/0x2890 kernel/locking/lockdep.c:5237
       lock_acquire kernel/locking/lockdep.c:5868 [inline]
       lock_acquire+0x179/0x330 kernel/locking/lockdep.c:5825
       __mutex_lock_common kernel/locking/mutex.c:614 [inline]
       __mutex_lock+0x1aa/0x1ca0 kernel/locking/mutex.c:776
       nbd_handle_cmd drivers/block/nbd.c:1143 [inline]
       nbd_queue_rq+0x423/0x12d0 drivers/block/nbd.c:1207
       blk_mq_dispatch_rq_list+0x416/0x1e20 block/blk-mq.c:2138
       __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+0xcbd/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:2376
       blk_mq_dispatch_list+0x514/0x1300 block/blk-mq.c:2939
       blk_mq_flush_plug_list block/blk-mq.c:2987 [inline]
       blk_mq_flush_plug_list+0x130/0x600 block/blk-mq.c:2959
       __blk_flush_plug+0x2c4/0x4b0 block/blk-core.c:1225
       blk_finish_plug block/blk-core.c:1252 [inline]
       blk_finish_plug block/blk-core.c:1249 [inline]
       __submit_bio+0x542/0x690 block/blk-core.c:651
       __submit_bio_noacct_mq block/blk-core.c:724 [inline]
       submit_bio_noacct_nocheck+0x53d/0xbe0 block/blk-core.c:755
       submit_bio_noacct+0x5bd/0x1f40 block/blk-core.c:879
       submit_bh fs/buffer.c:2829 [inline]
       block_read_full_folio+0x4db/0x850 fs/buffer.c:2461
       filemap_read_folio+0xc8/0x2a0 mm/filemap.c:2496
       do_read_cache_folio+0x266/0x5c0 mm/filemap.c:4096
       read_mapping_folio include/linux/pagemap.h:1017 [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:765
       bdev_open+0x2c7/0xe40 block/bdev.c:974
       blkdev_open+0x34e/0x4f0 block/fops.c:698
       do_dentry_open+0x748/0x1590 fs/open.c:962
       vfs_open+0x82/0x3f0 fs/open.c:1094
       do_open fs/namei.c:4628 [inline]
       path_openat+0x2078/0x3140 fs/namei.c:4787
       do_filp_open+0x20b/0x470 fs/namei.c:4814
       do_sys_openat2+0x121/0x290 fs/open.c:1430
       do_sys_open fs/open.c:1436 [inline]
       __do_sys_openat fs/open.c:1452 [inline]
       __se_sys_openat fs/open.c:1447 [inline]
       __x64_sys_openat+0x174/0x210 fs/open.c:1447
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xcd/0xf80 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/5819:
 #0: ffff88802656e358 (&disk->open_mutex){+.+.}-{4:4}, at: bdev_open+0x41a/0xe40 block/bdev.c:962
 #1: ffff88814173c118 (set->srcu){.+.+}-{0:0}, at: srcu_lock_acquire include/linux/srcu.h:185 [inline]
 #1: ffff88814173c118 (set->srcu){.+.+}-{0:0}, at: srcu_read_lock include/linux/srcu.h:277 [inline]
 #1: ffff88814173c118 (set->srcu){.+.+}-{0:0}, at: blk_mq_run_hw_queue+0x22b/0x670 block/blk-mq.c:2376
 #2: ffff888026610180 (&cmd->lock){+.+.}-{4:4}, at: nbd_queue_rq+0xbd/0x12d0 drivers/block/nbd.c:1199

stack backtrace:
CPU: 0 UID: 0 PID: 5819 Comm: udevd Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
 print_circular_bug+0x275/0x340 kernel/locking/lockdep.c:2043
 check_noncircular+0x146/0x160 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 kernel/locking/lockdep.c:3908 [inline]
 __lock_acquire+0x1669/0x2890 kernel/locking/lockdep.c:5237
 lock_acquire kernel/locking/lockdep.c:5868 [inline]
 lock_acquire+0x179/0x330 kernel/locking/lockdep.c:5825
 __mutex_lock_common kernel/locking/mutex.c:614 [inline]
 __mutex_lock+0x1aa/0x1ca0 kernel/locking/mutex.c:776
 nbd_handle_cmd drivers/block/nbd.c:1143 [inline]
 nbd_queue_rq+0x423/0x12d0 drivers/block/nbd.c:1207
 blk_mq_dispatch_rq_list+0x416/0x1e20 block/blk-mq.c:2138
 __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+0xcbd/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:2376
 blk_mq_dispatch_list+0x514/0x1300 block/blk-mq.c:2939
 blk_mq_flush_plug_list block/blk-mq.c:2987 [inline]
 blk_mq_flush_plug_list+0x130/0x600 block/blk-mq.c:2959
 __blk_flush_plug+0x2c4/0x4b0 block/blk-core.c:1225
 blk_finish_plug block/blk-core.c:1252 [inline]
 blk_finish_plug block/blk-core.c:1249 [inline]
 __submit_bio+0x542/0x690 block/blk-core.c:651
 __submit_bio_noacct_mq block/blk-core.c:724 [inline]
 submit_bio_noacct_nocheck+0x53d/0xbe0 block/blk-core.c:755
 submit_bio_noacct+0x5bd/0x1f40 block/blk-core.c:879
 submit_bh fs/buffer.c:2829 [inline]
 block_read_full_folio+0x4db/0x850 fs/buffer.c:2461
 filemap_read_folio+0xc8/0x2a0 mm/filemap.c:2496
 do_read_cache_folio+0x266/0x5c0 mm/filemap.c:4096
 read_mapping_folio include/linux/pagemap.h:1017 [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:765
 bdev_open+0x2c7/0xe40 block/bdev.c:974
 blkdev_open+0x34e/0x4f0 block/fops.c:698
 do_dentry_open+0x748/0x1590 fs/open.c:962
 vfs_open+0x82/0x3f0 fs/open.c:1094
 do_open fs/namei.c:4628 [inline]
 path_openat+0x2078/0x3140 fs/namei.c:4787
 do_filp_open+0x20b/0x470 fs/namei.c:4814
 do_sys_openat2+0x121/0x290 fs/open.c:1430
 do_sys_open fs/open.c:1436 [inline]
 __do_sys_openat fs/open.c:1452 [inline]
 __se_sys_openat fs/open.c:1447 [inline]
 __x64_sys_openat+0x174/0x210 fs/open.c:1447
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xcd/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fccbcca7407
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:00007fffc5a45640 EFLAGS: 00000202 ORIG_RAX: 0000000000000101
RAX: ffffffffffffffda RBX: 00007fccbd365880 RCX: 00007fccbcca7407
RDX: 00000000000a0800 RSI: 000055721aa7ea10 RDI: ffffffffffffff9c
RBP: 000055721aa65910 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000202 R12: 000055721aa7de00
R13: 000055721aa7d410 R14: 0000000000000000 R15: 000055721aa7de00
 </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 0x800000 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 0x800000 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 0x800000 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 0x800000 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 0x800000 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 0x800000 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 0x800000 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 0x800000 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 0x800000 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 0x800000 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