syzbot

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Tainted: G     U       L     
------------------------------------------------------
udevd/5813 is trying to acquire lock:
ffff88807e4f2470 (&nsock->tx_lock){+.+.}-{4:4}, at: nbd_handle_cmd drivers/block/nbd.c:1143 [inline]
ffff88807e4f2470 (&nsock->tx_lock){+.+.}-{4:4}, at: nbd_queue_rq+0x428/0x1080 drivers/block/nbd.c:1207

but task is already holding lock:
ffff888028280180 (&cmd->lock){+.+.}-{4:4}, at: nbd_queue_rq+0xba/0x1080 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+0x1a2/0x1b90 kernel/locking/mutex.c:776
       nbd_queue_rq+0xba/0x1080 drivers/block/nbd.c:1199
       blk_mq_dispatch_rq_list+0x422/0x1e70 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+0xcea/0x1620 block/blk-mq-sched.c:307
       blk_mq_sched_dispatch_requests+0xd7/0x1c0 block/blk-mq-sched.c:329
       blk_mq_run_hw_queue+0x23c/0x670 block/blk-mq.c:2386
       blk_mq_dispatch_list+0x51d/0x1360 block/blk-mq.c:2949
       blk_mq_flush_plug_list block/blk-mq.c:2997 [inline]
       blk_mq_flush_plug_list+0x130/0x600 block/blk-mq.c:2969
       __blk_flush_plug+0x2c4/0x4b0 block/blk-core.c:1230
       blk_finish_plug block/blk-core.c:1257 [inline]
       __submit_bio+0x584/0x6c0 block/blk-core.c:649
       __submit_bio_noacct_mq block/blk-core.c:722 [inline]
       submit_bio_noacct_nocheck+0x562/0xc10 block/blk-core.c:753
       submit_bio_noacct+0xd17/0x2010 block/blk-core.c:884
       blk_crypto_submit_bio include/linux/blk-crypto.h:203 [inline]
       submit_bh_wbc+0x59c/0x770 fs/buffer.c:2822
       submit_bh fs/buffer.c:2827 [inline]
       block_read_full_folio+0x4c8/0x8e0 fs/buffer.c:2459
       filemap_read_folio+0xfc/0x3b0 mm/filemap.c:2496
       do_read_cache_folio+0x2d7/0x6b0 mm/filemap.c:4096
       read_mapping_folio include/linux/pagemap.h:1028 [inline]
       read_part_sector+0xd1/0x370 block/partitions/core.c:723
       adfspart_check_ICS+0x93/0x910 block/partitions/acorn.c:360
       check_partition block/partitions/core.c:142 [inline]
       blk_add_partitions block/partitions/core.c:590 [inline]
       bdev_disk_changed+0x7f8/0xc80 block/partitions/core.c:694
       blkdev_get_whole+0x187/0x290 block/bdev.c:764
       bdev_open+0x2c7/0xe40 block/bdev.c:973
       blkdev_open+0x34e/0x4f0 block/fops.c:698
       do_dentry_open+0x6d8/0x1660 fs/open.c:949
       vfs_open+0x82/0x3f0 fs/open.c:1081
       do_open fs/namei.c:4671 [inline]
       path_openat+0x208c/0x31a0 fs/namei.c:4830
       do_file_open+0x20e/0x430 fs/namei.c:4859
       do_sys_openat2+0x10d/0x1e0 fs/open.c:1366
       do_sys_open fs/open.c:1372 [inline]
       __do_sys_openat fs/open.c:1388 [inline]
       __se_sys_openat fs/open.c:1383 [inline]
       __x64_sys_openat+0x12d/0x210 fs/open.c:1383
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x106/0xf80 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:199 [inline]
       __synchronize_srcu+0xa1/0x2a0 kernel/rcu/srcutree.c:1504
       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+0x412/0x590 block/blk-sysfs.c:940
       __add_disk+0x73f/0xe40 block/genhd.c:528
       add_disk_fwnode+0x118/0x5c0 block/genhd.c:597
       add_disk include/linux/blkdev.h:785 [inline]
       nbd_dev_add+0x77a/0xb10 drivers/block/nbd.c:1984
       nbd_init+0x291/0x2b0 drivers/block/nbd.c:2692
       do_one_initcall+0x11d/0x760 init/main.c:1382
       do_initcall_level init/main.c:1444 [inline]
       do_initcalls init/main.c:1460 [inline]
       do_basic_setup init/main.c:1479 [inline]
       kernel_init_freeable+0x6e5/0x7a0 init/main.c:1692
       kernel_init+0x1f/0x1e0 init/main.c:1582
       ret_from_fork+0x754/0xd80 arch/x86/kernel/process.c:158
       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:614 [inline]
       __mutex_lock+0x1a2/0x1b90 kernel/locking/mutex.c:776
       queue_requests_store+0x38b/0x660 block/blk-sysfs.c:117
       queue_attr_store+0x25f/0x2f0 block/blk-sysfs.c:866
       sysfs_kf_write+0xf2/0x150 fs/sysfs/file.c:142
       kernfs_fop_write_iter+0x3e0/0x5f0 fs/kernfs/file.c:352
       new_sync_write fs/read_write.c:595 [inline]
       vfs_write+0x6ac/0x1070 fs/read_write.c:688
       ksys_write+0x12a/0x250 fs/read_write.c:740
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x106/0xf80 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #3 (&q->q_usage_counter(io)#52){++++}-{0:0}:
       blk_alloc_queue+0x610/0x790 block/blk-core.c:461
       blk_mq_alloc_queue+0x174/0x290 block/blk-mq.c:4429
       __blk_mq_alloc_disk+0x29/0x120 block/blk-mq.c:4476
       nbd_dev_add+0x492/0xb10 drivers/block/nbd.c:1954
       nbd_init+0x291/0x2b0 drivers/block/nbd.c:2692
       do_one_initcall+0x11d/0x760 init/main.c:1382
       do_initcall_level init/main.c:1444 [inline]
       do_initcalls init/main.c:1460 [inline]
       do_basic_setup init/main.c:1479 [inline]
       kernel_init_freeable+0x6e5/0x7a0 init/main.c:1692
       kernel_init+0x1f/0x1e0 init/main.c:1582
       ret_from_fork+0x754/0xd80 arch/x86/kernel/process.c:158
       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:4347 [inline]
       fs_reclaim_acquire+0xc4/0x100 mm/page_alloc.c:4361
       might_alloc include/linux/sched/mm.h:317 [inline]
       slab_pre_alloc_hook mm/slub.c:4452 [inline]
       slab_alloc_node mm/slub.c:4807 [inline]
       __kmalloc_cache_noprof+0x4b/0x6f0 mm/slub.c:5334
       kmalloc_noprof include/linux/slab.h:962 [inline]
       kzalloc_noprof include/linux/slab.h:1204 [inline]
       tcp_sendmsg_fastopen+0x24d/0x750 net/ipv4/tcp.c:1080
       tcp_sendmsg_locked+0x279a/0x45f0 net/ipv4/tcp.c:1194
       tcp_sendmsg+0x2e/0x50 net/ipv4/tcp.c:1464
       inet6_sendmsg+0xb9/0x140 net/ipv6/af_inet6.c:659
       smc_sendmsg+0x230/0x540 net/smc/af_smc.c:2812
       sock_sendmsg_nosec net/socket.c:727 [inline]
       __sock_sendmsg net/socket.c:742 [inline]
       ____sys_sendmsg+0xa54/0xc30 net/socket.c:2592
       ___sys_sendmsg+0x190/0x1e0 net/socket.c:2646
       __sys_sendmsg+0x170/0x220 net/socket.c:2678
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x106/0xf80 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (k-sk_lock-AF_INET6){+.+.}-{0:0}:
       lock_sock_nested+0x41/0xf0 net/core/sock.c:3780
       lock_sock include/net/sock.h:1709 [inline]
       inet_shutdown+0x67/0x410 net/ipv4/af_inet.c:913
       nbd_mark_nsock_dead+0xae/0x5c0 drivers/block/nbd.c:318
       sock_shutdown+0x16b/0x200 drivers/block/nbd.c:411
       nbd_clear_sock drivers/block/nbd.c:1427 [inline]
       nbd_config_put+0x1eb/0x750 drivers/block/nbd.c:1451
       nbd_release+0xb7/0x190 drivers/block/nbd.c:1756
       blkdev_put_whole+0xb0/0xf0 block/bdev.c:737
       bdev_release+0x47f/0x6d0 block/bdev.c:1160
       blkdev_release+0x15/0x20 block/fops.c:706
       __fput+0x3ff/0xb40 fs/file_table.c:469
       task_work_run+0x150/0x240 kernel/task_work.c:233
       exit_task_work include/linux/task_work.h:40 [inline]
       do_exit+0x829/0x2aa0 kernel/exit.c:971
       do_group_exit+0xd5/0x2a0 kernel/exit.c:1112
       get_signal+0x1ec7/0x21e0 kernel/signal.c:3034
       arch_do_signal_or_restart+0x91/0x770 arch/x86/kernel/signal.c:337
       __exit_to_user_mode_loop kernel/entry/common.c:64 [inline]
       exit_to_user_mode_loop+0x86/0x4a0 kernel/entry/common.c:98
       __exit_to_user_mode_prepare include/linux/irq-entry-common.h:226 [inline]
       syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:256 [inline]
       syscall_exit_to_user_mode include/linux/entry-common.h:325 [inline]
       do_syscall_64+0x668/0xf80 arch/x86/entry/syscall_64.c:100
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #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+0x14b8/0x2630 kernel/locking/lockdep.c:5237
       lock_acquire kernel/locking/lockdep.c:5868 [inline]
       lock_acquire+0x1cf/0x380 kernel/locking/lockdep.c:5825
       __mutex_lock_common kernel/locking/mutex.c:614 [inline]
       __mutex_lock+0x1a2/0x1b90 kernel/locking/mutex.c:776
       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: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+0xcea/0x1620 block/blk-mq-sched.c:307
       blk_mq_sched_dispatch_requests+0xd7/0x1c0 block/blk-mq-sched.c:329
       blk_mq_run_hw_queue+0x23c/0x670 block/blk-mq.c:2386
       blk_mq_dispatch_list+0x51d/0x1360 block/blk-mq.c:2949
       blk_mq_flush_plug_list block/blk-mq.c:2997 [inline]
       blk_mq_flush_plug_list+0x130/0x600 block/blk-mq.c:2969
       __blk_flush_plug+0x2c4/0x4b0 block/blk-core.c:1230
       blk_finish_plug block/blk-core.c:1257 [inline]
       __submit_bio+0x584/0x6c0 block/blk-core.c:649
       __submit_bio_noacct_mq block/blk-core.c:722 [inline]
       submit_bio_noacct_nocheck+0x562/0xc10 block/blk-core.c:753
       submit_bio_noacct+0xd17/0x2010 block/blk-core.c:884
       blk_crypto_submit_bio include/linux/blk-crypto.h:203 [inline]
       submit_bh_wbc+0x59c/0x770 fs/buffer.c:2822
       submit_bh fs/buffer.c:2827 [inline]
       block_read_full_folio+0x4c8/0x8e0 fs/buffer.c:2459
       filemap_read_folio+0xfc/0x3b0 mm/filemap.c:2496
       do_read_cache_folio+0x2d7/0x6b0 mm/filemap.c:4096
       read_mapping_folio include/linux/pagemap.h:1028 [inline]
       read_part_sector+0xd1/0x370 block/partitions/core.c:723
       adfspart_check_ICS+0x93/0x910 block/partitions/acorn.c:360
       check_partition block/partitions/core.c:142 [inline]
       blk_add_partitions block/partitions/core.c:590 [inline]
       bdev_disk_changed+0x7f8/0xc80 block/partitions/core.c:694
       blkdev_get_whole+0x187/0x290 block/bdev.c:764
       bdev_open+0x2c7/0xe40 block/bdev.c:973
       blkdev_open+0x34e/0x4f0 block/fops.c:698
       do_dentry_open+0x6d8/0x1660 fs/open.c:949
       vfs_open+0x82/0x3f0 fs/open.c:1081
       do_open fs/namei.c:4671 [inline]
       path_openat+0x208c/0x31a0 fs/namei.c:4830
       do_file_open+0x20e/0x430 fs/namei.c:4859
       do_sys_openat2+0x10d/0x1e0 fs/open.c:1366
       do_sys_open fs/open.c:1372 [inline]
       __do_sys_openat fs/open.c:1388 [inline]
       __se_sys_openat fs/open.c:1383 [inline]
       __x64_sys_openat+0x12d/0x210 fs/open.c:1383
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x106/0xf80 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/5813:
 #0: ffff888028243358 (&disk->open_mutex){+.+.}-{4:4}, at: bdev_open+0x41a/0xe40 block/bdev.c:961
 #1: ffff88802756a598 (set->srcu){.+.+}-{0:0}, at: srcu_lock_acquire include/linux/srcu.h:187 [inline]
 #1: ffff88802756a598 (set->srcu){.+.+}-{0:0}, at: srcu_read_lock include/linux/srcu.h:294 [inline]
 #1: ffff88802756a598 (set->srcu){.+.+}-{0:0}, at: blk_mq_run_hw_queue+0x22e/0x670 block/blk-mq.c:2386
 #2: ffff888028280180 (&cmd->lock){+.+.}-{4:4}, at: nbd_queue_rq+0xba/0x1080 drivers/block/nbd.c:1199

stack backtrace:
CPU: 1 UID: 0 PID: 5813 Comm: udevd Tainted: G     U       L      syzkaller #0 PREEMPT(full) 
Tainted: [U]=USER, [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
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 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+0x14b8/0x2630 kernel/locking/lockdep.c:5237
 lock_acquire kernel/locking/lockdep.c:5868 [inline]
 lock_acquire+0x1cf/0x380 kernel/locking/lockdep.c:5825
 __mutex_lock_common kernel/locking/mutex.c:614 [inline]
 __mutex_lock+0x1a2/0x1b90 kernel/locking/mutex.c:776
 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: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+0xcea/0x1620 block/blk-mq-sched.c:307
 blk_mq_sched_dispatch_requests+0xd7/0x1c0 block/blk-mq-sched.c:329
 blk_mq_run_hw_queue+0x23c/0x670 block/blk-mq.c:2386
 blk_mq_dispatch_list+0x51d/0x1360 block/blk-mq.c:2949
 blk_mq_flush_plug_list block/blk-mq.c:2997 [inline]
 blk_mq_flush_plug_list+0x130/0x600 block/blk-mq.c:2969
 __blk_flush_plug+0x2c4/0x4b0 block/blk-core.c:1230
 blk_finish_plug block/blk-core.c:1257 [inline]
 __submit_bio+0x584/0x6c0 block/blk-core.c:649
 __submit_bio_noacct_mq block/blk-core.c:722 [inline]
 submit_bio_noacct_nocheck+0x562/0xc10 block/blk-core.c:753
 submit_bio_noacct+0xd17/0x2010 block/blk-core.c:884
 blk_crypto_submit_bio include/linux/blk-crypto.h:203 [inline]
 submit_bh_wbc+0x59c/0x770 fs/buffer.c:2822
 submit_bh fs/buffer.c:2827 [inline]
 block_read_full_folio+0x4c8/0x8e0 fs/buffer.c:2459
 filemap_read_folio+0xfc/0x3b0 mm/filemap.c:2496
 do_read_cache_folio+0x2d7/0x6b0 mm/filemap.c:4096
 read_mapping_folio include/linux/pagemap.h:1028 [inline]
 read_part_sector+0xd1/0x370 block/partitions/core.c:723
 adfspart_check_ICS+0x93/0x910 block/partitions/acorn.c:360
 check_partition block/partitions/core.c:142 [inline]
 blk_add_partitions block/partitions/core.c:590 [inline]
 bdev_disk_changed+0x7f8/0xc80 block/partitions/core.c:694
 blkdev_get_whole+0x187/0x290 block/bdev.c:764
 bdev_open+0x2c7/0xe40 block/bdev.c:973
 blkdev_open+0x34e/0x4f0 block/fops.c:698
 do_dentry_open+0x6d8/0x1660 fs/open.c:949
 vfs_open+0x82/0x3f0 fs/open.c:1081
 do_open fs/namei.c:4671 [inline]
 path_openat+0x208c/0x31a0 fs/namei.c:4830
 do_file_open+0x20e/0x430 fs/namei.c:4859
 do_sys_openat2+0x10d/0x1e0 fs/open.c:1366
 do_sys_open fs/open.c:1372 [inline]
 __do_sys_openat fs/open.c:1388 [inline]
 __se_sys_openat fs/open.c:1383 [inline]
 __x64_sys_openat+0x12d/0x210 fs/open.c:1383
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x106/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f1e40aa7407
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:00007ffc4548a830 EFLAGS: 00000202 ORIG_RAX: 0000000000000101
RAX: ffffffffffffffda RBX: 00007f1e4115b880 RCX: 00007f1e40aa7407
RDX: 00000000000a0800 RSI: 000055c2fd977500 RDI: ffffffffffffff9c
RBP: 000055c2fd977910 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000202 R12: 000055c2fd98fe00
R13: 000055c2fd98f410 R14: 0000000000000000 R15: 000055c2fd98fe00
 </TASK>