[v6.1] possible deadlock in blkdev_put

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 090666d3cc90 Linux 6.1.177
git tree: linux-6.1.y
console output: https://syzkaller.appspot.com/x/log.txt?x=166c9b89580000
kernel config: https://syzkaller.appspot.com/x/.config?x=f5aae664b2df43c2
dashboard link: https://syzkaller.appspot.com/bug?extid=f3ec913e8a06b0a45134
compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/0b218516a5e9/disk-090666d3.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/3239ad568bdf/vmlinux-090666d3.xz
kernel image: https://storage.googleapis.com/syzbot-assets/a8b19cfbec3e/bzImage-090666d3.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+f3ec91...@syzkaller.appspotmail.com

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


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