[v6.6] possible deadlock in blkdev_put (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 8cee53b8eaeb Linux 6.6.134
git tree: linux-6.6.y
console output: https://syzkaller.appspot.com/x/log.txt?x=136fd106580000
kernel config: https://syzkaller.appspot.com/x/.config?x=c5b35c4db8465904
dashboard link: https://syzkaller.appspot.com/bug?extid=ae56c2adbd4c58956e49
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/4c0eb6df7b4a/disk-8cee53b8.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/38626ee912e4/vmlinux-8cee53b8.xz
kernel image: https://storage.googleapis.com/syzbot-assets/646a84f3433a/bzImage-8cee53b8.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+ae56c2...@syzkaller.appspotmail.com

block device autoloading is deprecated and will be removed.
EXT4-fs (loop1): external journal has bad superblock
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.1.553/7533 is trying to acquire lock:
ffff888020e494c8 (&disk->open_mutex){+.+.}-{3:3}, at: blkdev_put+0xff/0x760 block/bdev.c:944

but task is already holding lock:
ffff88802ec6a0e0 (&type->s_umount_key#32){++++}-{3:3}, at: ext4_get_journal_blkdev fs/ext4/super.c:5902 [inline]
ffff88802ec6a0e0 (&type->s_umount_key#32){++++}-{3:3}, at: ext4_open_dev_journal fs/ext4/super.c:5974 [inline]
ffff88802ec6a0e0 (&type->s_umount_key#32){++++}-{3:3}, at: ext4_load_journal fs/ext4/super.c:6037 [inline]
ffff88802ec6a0e0 (&type->s_umount_key#32){++++}-{3:3}, at: ext4_load_and_init_journal+0x280/0x2100 fs/ext4/super.c:4923

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (&type->s_umount_key#32){++++}-{3:3}:
down_read+0x46/0x2e0 kernel/locking/rwsem.c:1520
__super_lock fs/super.c:58 [inline]
super_lock+0x17f/0x3a0 fs/super.c:117
super_lock_shared fs/super.c:146 [inline]
super_lock_shared_active fs/super.c:1442 [inline]
fs_bdev_sync+0xa4/0x170 fs/super.c:1477
blkdev_flushbuf block/ioctl.c:381 [inline]
blkdev_common_ioctl+0x8a6/0x2570 block/ioctl.c:511
blkdev_ioctl+0x512/0x730 block/ioctl.c:633
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:871 [inline]
__se_sys_ioctl+0xfd/0x170 fs/ioctl.c:857
do_syscall_x64 arch/x86/entry/common.c:46 [inline]
do_syscall_64+0x55/0xa0 arch/x86/entry/common.c:76
entry_SYSCALL_64_after_hwframe+0x68/0xd2

-> #1 (&bdev->bd_holder_lock){+.+.}-{3:3}:
__mutex_lock_common kernel/locking/mutex.c:603 [inline]
__mutex_lock+0x136/0xcc0 kernel/locking/mutex.c:747
bdev_mark_dead+0x31/0x1a0 block/bdev.c:1028
disk_force_media_change+0x14e/0x1d0 block/disk-events.c:302
__loop_clr_fd+0x396/0x660 drivers/block/loop.c:1170
blkdev_put+0x5bd/0x760 block/bdev.c:-1
bdev_release+0x57/0x70 block/bdev.c:968
kill_f2fs_super+0x326/0x3d0 fs/f2fs/super.c:4883
deactivate_locked_super+0x97/0x100 fs/super.c:481
cleanup_mnt+0x43b/0x4d0 fs/namespace.c:1259
task_work_run+0x1d4/0x260 kernel/task_work.c:245
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:291 [inline]
syscall_exit_to_user_mode+0x1a/0x50 kernel/entry/common.c:302
do_syscall_64+0x61/0xa0 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:3134 [inline]
check_prevs_add kernel/locking/lockdep.c:3253 [inline]
validate_chain kernel/locking/lockdep.c:3869 [inline]
__lock_acquire+0x2df1/0x7d40 kernel/locking/lockdep.c:5137
lock_acquire+0x19e/0x420 kernel/locking/lockdep.c:5754
__mutex_lock_common kernel/locking/mutex.c:603 [inline]
__mutex_lock+0x136/0xcc0 kernel/locking/mutex.c:747
blkdev_put+0xff/0x760 block/bdev.c:944
ext4_get_journal_blkdev fs/ext4/super.c:5961 [inline]
ext4_open_dev_journal fs/ext4/super.c:5974 [inline]
ext4_load_journal fs/ext4/super.c:6037 [inline]
ext4_load_and_init_journal+0xcef/0x2100 fs/ext4/super.c:4923
__ext4_fill_super fs/ext4/super.c:5411 [inline]
ext4_fill_super+0x430a/0x67b0 fs/ext4/super.c:5744
get_tree_bdev+0x3f3/0x520 fs/super.c:1591
vfs_get_tree+0x8c/0x280 fs/super.c:1764
do_new_mount+0x24b/0xa40 fs/namespace.c:3386
do_mount fs/namespace.c:3726 [inline]
__do_sys_mount fs/namespace.c:3935 [inline]
__se_sys_mount+0x2e7/0x3d0 fs/namespace.c:3912
do_syscall_x64 arch/x86/entry/common.c:46 [inline]
do_syscall_64+0x55/0xa0 arch/x86/entry/common.c:76
entry_SYSCALL_64_after_hwframe+0x68/0xd2

other info that might help us debug this:

Chain exists of:
&disk->open_mutex --> &bdev->bd_holder_lock --> &type->s_umount_key#32

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(&type->s_umount_key#32);
lock(&bdev->bd_holder_lock);
lock(&type->s_umount_key#32);
lock(&disk->open_mutex);

*** DEADLOCK ***

1 lock held by syz.1.553/7533:
#0: ffff88802ec6a0e0 (&type->s_umount_key#32){++++}-{3:3}, at: ext4_get_journal_blkdev fs/ext4/super.c:5902 [inline]
#0: ffff88802ec6a0e0 (&type->s_umount_key#32){++++}-{3:3}, at: ext4_open_dev_journal fs/ext4/super.c:5974 [inline]
#0: ffff88802ec6a0e0 (&type->s_umount_key#32){++++}-{3:3}, at: ext4_load_journal fs/ext4/super.c:6037 [inline]
#0: ffff88802ec6a0e0 (&type->s_umount_key#32){++++}-{3:3}, at: ext4_load_and_init_journal+0x280/0x2100 fs/ext4/super.c:4923

stack backtrace:
CPU: 0 PID: 7533 Comm: syz.1.553 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/18/2026
Call Trace:
<TASK>
dump_stack_lvl+0x18c/0x250 lib/dump_stack.c:106
check_noncircular+0x2fc/0x400 kernel/locking/lockdep.c:2187
check_prev_add kernel/locking/lockdep.c:3134 [inline]
check_prevs_add kernel/locking/lockdep.c:3253 [inline]
validate_chain kernel/locking/lockdep.c:3869 [inline]
__lock_acquire+0x2df1/0x7d40 kernel/locking/lockdep.c:5137
lock_acquire+0x19e/0x420 kernel/locking/lockdep.c:5754
__mutex_lock_common kernel/locking/mutex.c:603 [inline]
__mutex_lock+0x136/0xcc0 kernel/locking/mutex.c:747
blkdev_put+0xff/0x760 block/bdev.c:944
ext4_get_journal_blkdev fs/ext4/super.c:5961 [inline]
ext4_open_dev_journal fs/ext4/super.c:5974 [inline]
ext4_load_journal fs/ext4/super.c:6037 [inline]
ext4_load_and_init_journal+0xcef/0x2100 fs/ext4/super.c:4923
__ext4_fill_super fs/ext4/super.c:5411 [inline]
ext4_fill_super+0x430a/0x67b0 fs/ext4/super.c:5744
get_tree_bdev+0x3f3/0x520 fs/super.c:1591
vfs_get_tree+0x8c/0x280 fs/super.c:1764
do_new_mount+0x24b/0xa40 fs/namespace.c:3386
do_mount fs/namespace.c:3726 [inline]
__do_sys_mount fs/namespace.c:3935 [inline]
__se_sys_mount+0x2e7/0x3d0 fs/namespace.c:3912
do_syscall_x64 arch/x86/entry/common.c:46 [inline]
do_syscall_64+0x55/0xa0 arch/x86/entry/common.c:76
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f8baa59da8a
Code: 48 c7 c2 e8 ff ff ff f7 d8 64 89 02 b8 ff ff ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 49 89 ca b8 a5 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f8bab3d8e58 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00007f8bab3d8ee0 RCX: 00007f8baa59da8a
RDX: 0000200000000180 RSI: 0000200000000480 RDI: 00007f8bab3d8ea0
RBP: 0000200000000180 R08: 00007f8bab3d8ee0 R09: 00000000c0ed4040
R10: 00000000c0ed4040 R11: 0000000000000246 R12: 0000200000000480
R13: 00007f8bab3d8ea0 R14: 000000000000047a R15: 00002000000004c0
</TASK>
netlink: 12 bytes leftover after parsing attributes in process `syz.1.553'.
ipvlan2: entered allmulticast mode
syz_tun: entered allmulticast mode


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