syzbot

XFS (loop7): Unmounting Filesystem
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz-executor/6527 is trying to acquire lock:
ffff888024b7b4c8 (&disk->open_mutex){+.+.}-{3:3}, at: blkdev_put+0xf7/0x780 block/bdev.c:930

but task is already holding lock:
ffff8880245400e0 (&type->s_umount_key#59){++++}-{3:3}, at: deactivate_super+0xa0/0xd0 fs/super.c:362

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (&type->s_umount_key#59){++++}-{3:3}:
       down_read+0x42/0x2d0 kernel/locking/rwsem.c:1520
       get_super+0x102/0x200 fs/super.c:828
       __invalidate_device+0x19/0xf0 block/bdev.c:1022
       nbd_clear_sock_ioctl drivers/block/nbd.c:1463 [inline]
       __nbd_ioctl drivers/block/nbd.c:1490 [inline]
       nbd_ioctl+0x368/0xed0 drivers/block/nbd.c:1550
       blkdev_ioctl+0x37b/0x740 block/ioctl.c:626
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:870 [inline]
       __se_sys_ioctl+0xfa/0x170 fs/ioctl.c:856
       do_syscall_x64 arch/x86/entry/common.c:46 [inline]
       do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:76
       entry_SYSCALL_64_after_hwframe+0x68/0xd2

-> #1 (&nbd->config_lock){+.+.}-{3:3}:
       __mutex_lock_common kernel/locking/mutex.c:603 [inline]
       __mutex_lock+0x12d/0xae0 kernel/locking/mutex.c:747
       refcount_dec_and_mutex_lock+0x2c/0xa0 lib/refcount.c:118
       nbd_config_put+0x2c/0x760 drivers/block/nbd.c:1328
       nbd_release+0xfa/0x130 drivers/block/nbd.c:1632
       blkdev_put+0x5b4/0x780 block/bdev.c:-1
       blkdev_close+0x51/0x80 block/fops.c:514
       __fput+0x20a/0x8b0 fs/file_table.c:320
       task_work_run+0x1d0/0x260 kernel/task_work.c:203
       resume_user_mode_work include/linux/resume_user_mode.h:49 [inline]
       exit_to_user_mode_loop+0xe6/0x110 kernel/entry/common.c:177
       exit_to_user_mode_prepare+0xee/0x180 kernel/entry/common.c:210
       __syscall_exit_to_user_mode_work kernel/entry/common.c:292 [inline]
       syscall_exit_to_user_mode+0x16/0x40 kernel/entry/common.c:303
       do_syscall_64+0x58/0xa0 arch/x86/entry/common.c:82
       entry_SYSCALL_64_after_hwframe+0x68/0xd2

-> #0 (&disk->open_mutex){+.+.}-{3:3}:
       check_prev_add kernel/locking/lockdep.c:3095 [inline]
       check_prevs_add kernel/locking/lockdep.c:3214 [inline]
       validate_chain kernel/locking/lockdep.c:3830 [inline]
       __lock_acquire+0x2d18/0x7c40 kernel/locking/lockdep.c:5063
       lock_acquire+0x1bb/0x4a0 kernel/locking/lockdep.c:5676
       __mutex_lock_common kernel/locking/mutex.c:603 [inline]
       __mutex_lock+0x12d/0xae0 kernel/locking/mutex.c:747
       blkdev_put+0xf7/0x780 block/bdev.c:930
       xfs_close_devices+0xf3/0x130 fs/xfs/xfs_super.c:409
       xfs_fs_put_super+0x242/0x2c0 fs/xfs/xfs_super.c:1126
       generic_shutdown_super+0x130/0x340 fs/super.c:501
       kill_block_super+0x7c/0xe0 fs/super.c:1470
       deactivate_locked_super+0x93/0xf0 fs/super.c:332
       cleanup_mnt+0x471/0x4f0 fs/namespace.c:1191
       task_work_run+0x1d0/0x260 kernel/task_work.c:203
       resume_user_mode_work include/linux/resume_user_mode.h:49 [inline]
       exit_to_user_mode_loop+0xe6/0x110 kernel/entry/common.c:177
       exit_to_user_mode_prepare+0xee/0x180 kernel/entry/common.c:210
       __syscall_exit_to_user_mode_work kernel/entry/common.c:292 [inline]
       syscall_exit_to_user_mode+0x16/0x40 kernel/entry/common.c:303
       do_syscall_64+0x58/0xa0 arch/x86/entry/common.c:82
       entry_SYSCALL_64_after_hwframe+0x68/0xd2

other info that might help us debug this:

Chain exists of:
  &disk->open_mutex --> &nbd->config_lock --> &type->s_umount_key#59

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&type->s_umount_key#59);
                               lock(&nbd->config_lock);
                               lock(&type->s_umount_key#59);
  lock(&disk->open_mutex);

 *** DEADLOCK ***

1 lock held by syz-executor/6527:
 #0: ffff8880245400e0 (&type->s_umount_key#59){++++}-{3:3}, at: deactivate_super+0xa0/0xd0 fs/super.c:362

stack backtrace:
CPU: 1 PID: 6527 Comm: syz-executor Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0x188/0x24e lib/dump_stack.c:106
 check_noncircular+0x296/0x330 kernel/locking/lockdep.c:2170
 check_prev_add kernel/locking/lockdep.c:3095 [inline]
 check_prevs_add kernel/locking/lockdep.c:3214 [inline]
 validate_chain kernel/locking/lockdep.c:3830 [inline]
 __lock_acquire+0x2d18/0x7c40 kernel/locking/lockdep.c:5063
 lock_acquire+0x1bb/0x4a0 kernel/locking/lockdep.c:5676
 __mutex_lock_common kernel/locking/mutex.c:603 [inline]
 __mutex_lock+0x12d/0xae0 kernel/locking/mutex.c:747
 blkdev_put+0xf7/0x780 block/bdev.c:930
 xfs_close_devices+0xf3/0x130 fs/xfs/xfs_super.c:409
 xfs_fs_put_super+0x242/0x2c0 fs/xfs/xfs_super.c:1126
 generic_shutdown_super+0x130/0x340 fs/super.c:501
 kill_block_super+0x7c/0xe0 fs/super.c:1470
 deactivate_locked_super+0x93/0xf0 fs/super.c:332
 cleanup_mnt+0x471/0x4f0 fs/namespace.c:1191
 task_work_run+0x1d0/0x260 kernel/task_work.c:203
 resume_user_mode_work include/linux/resume_user_mode.h:49 [inline]
 exit_to_user_mode_loop+0xe6/0x110 kernel/entry/common.c:177
 exit_to_user_mode_prepare+0xee/0x180 kernel/entry/common.c:210
 __syscall_exit_to_user_mode_work kernel/entry/common.c:292 [inline]
 syscall_exit_to_user_mode+0x16/0x40 kernel/entry/common.c:303
 do_syscall_64+0x58/0xa0 arch/x86/entry/common.c:82
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7fc0ce19f097
Code: a2 c7 05 5c 26 25 00 00 00 00 00 eb 96 e8 e1 12 00 00 90 31 f6 e9 09 00 00 00 66 0f 1f 84 00 00 00 00 00 b8 a6 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 01 c3 48 c7 c2 e8 ff ff ff f7 d8 64 89 02 b8
RSP: 002b:00007ffc047c0a88 EFLAGS: 00000202 ORIG_RAX: 00000000000000a6
RAX: 0000000000000000 RBX: 0000000000000064 RCX: 00007fc0ce19f097
RDX: 0000000000000200 RSI: 0000000000000009 RDI: 00007ffc047c1c30
RBP: 00007fc0ce2332ca R08: 0000000000020590 R09: 00000000ffffffff
R10: 0000000000000100 R11: 0000000000000202 R12: 00007ffc047c1c30
R13: 00007fc0ce2332ca R14: 00005555559504e8 R15: 00007ffc047c2d00
 </TASK>
BTRFS info (device loop7): last unmount of filesystem c9fe44da-de57-406a-8241-57ec7d4412cf