[v5.15] possible deadlock in chmod_common (3)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 68efe5a6c16a Linux 5.15.197
git tree: linux-5.15.y
console output: https://syzkaller.appspot.com/x/log.txt?x=15dfc19a580000
kernel config: https://syzkaller.appspot.com/x/.config?x=7e6ed99963d6ee1d
dashboard link: https://syzkaller.appspot.com/bug?extid=8771aa70602d6ed0037d
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=13dfc19a580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=17f16922580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/900f9b9bd850/disk-68efe5a6.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/1e089a5019a6/vmlinux-68efe5a6.xz
kernel image: https://storage.googleapis.com/syzbot-assets/b319f477b907/bzImage-68efe5a6.xz
mounted in repro #1: https://storage.googleapis.com/syzbot-assets/0781ceff3af7/mount_0.gz
fsck result: failed (log: https://syzkaller.appspot.com/x/fsck.log?x=11dfc19a580000)
mounted in repro #2: https://storage.googleapis.com/syzbot-assets/f28fcca43a08/mount_3.gz
fsck result: failed (log: https://syzkaller.appspot.com/x/fsck.log?x=13f16922580000)

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+8771aa...@syzkaller.appspotmail.com

REISERFS (device loop2): checking transaction log (loop2)
REISERFS (device loop2): Using tea hash to sort names
REISERFS (device loop2): Created .reiserfs_priv - reserved for xattr storage.
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.2.65/4556 is trying to acquire lock:
ffff88805bbc3140 (&type->i_mutex_dir_key#8){+.+.}-{3:3}, at: inode_lock include/linux/fs.h:787 [inline]
ffff88805bbc3140 (&type->i_mutex_dir_key#8){+.+.}-{3:3}, at: chmod_common+0x184/0x3f0 fs/open.c:576

but task is already holding lock:
ffff88802237e460 (sb_writers#13){.+.+}-{0:0}, at: mnt_want_write+0x3d/0x90 fs/namespace.c:386

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (sb_writers#13){.+.+}-{0:0}:
percpu_down_read include/linux/percpu-rwsem.h:51 [inline]
__sb_start_write include/linux/fs.h:1811 [inline]
sb_start_write+0x4f/0x1c0 include/linux/fs.h:1881
mnt_want_write_file+0x5c/0x200 fs/namespace.c:430
reiserfs_ioctl+0x10a/0x330 fs/reiserfs/ioctl.c:103
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:874 [inline]
__se_sys_ioctl+0xfa/0x170 fs/ioctl.c:860
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x66/0xd0

-> #1 (&sbi->lock){+.+.}-{3:3}:
__mutex_lock_common+0x1eb/0x2390 kernel/locking/mutex.c:596
__mutex_lock kernel/locking/mutex.c:729 [inline]
mutex_lock_nested+0x17/0x20 kernel/locking/mutex.c:743
reiserfs_write_lock+0x75/0xd0 fs/reiserfs/lock.c:27
reiserfs_lookup+0x137/0x420 fs/reiserfs/namei.c:364
__lookup_slow+0x27d/0x3d0 fs/namei.c:1671
lookup_one_len+0x18e/0x2c0 fs/namei.c:2726
reiserfs_lookup_privroot+0x85/0x1e0 fs/reiserfs/xattr.c:980
reiserfs_fill_super+0x1760/0x23e0 fs/reiserfs/super.c:2196
mount_bdev+0x287/0x3c0 fs/super.c:1400
legacy_get_tree+0xe6/0x180 fs/fs_context.c:611
vfs_get_tree+0x88/0x270 fs/super.c:1530
do_new_mount+0x24a/0xa40 fs/namespace.c:3034
do_mount fs/namespace.c:3377 [inline]
__do_sys_mount fs/namespace.c:3585 [inline]
__se_sys_mount+0x2d6/0x3c0 fs/namespace.c:3562
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x66/0xd0

-> #0 (&type->i_mutex_dir_key#8){+.+.}-{3:3}:
check_prev_add kernel/locking/lockdep.c:3053 [inline]
check_prevs_add kernel/locking/lockdep.c:3172 [inline]
validate_chain kernel/locking/lockdep.c:3788 [inline]
__lock_acquire+0x2c33/0x7c60 kernel/locking/lockdep.c:5012
lock_acquire+0x197/0x3f0 kernel/locking/lockdep.c:5623
down_write+0x38/0x60 kernel/locking/rwsem.c:1551
inode_lock include/linux/fs.h:787 [inline]
chmod_common+0x184/0x3f0 fs/open.c:576
vfs_fchmod fs/open.c:598 [inline]
__do_sys_fchmod fs/open.c:607 [inline]
__se_sys_fchmod fs/open.c:601 [inline]
__x64_sys_fchmod+0xee/0x150 fs/open.c:601
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x66/0xd0

other info that might help us debug this:

Chain exists of:
&type->i_mutex_dir_key#8 --> &sbi->lock --> sb_writers#13

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(sb_writers#13);
lock(&sbi->lock);
lock(sb_writers#13);
lock(&type->i_mutex_dir_key#8);

*** DEADLOCK ***

1 lock held by syz.2.65/4556:
#0: ffff88802237e460 (sb_writers#13){.+.+}-{0:0}, at: mnt_want_write+0x3d/0x90 fs/namespace.c:386

stack backtrace:
CPU: 0 PID: 4556 Comm: syz.2.65 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Call Trace:
<TASK>
dump_stack_lvl+0x168/0x230 lib/dump_stack.c:106
check_noncircular+0x274/0x310 kernel/locking/lockdep.c:2133
check_prev_add kernel/locking/lockdep.c:3053 [inline]
check_prevs_add kernel/locking/lockdep.c:3172 [inline]
validate_chain kernel/locking/lockdep.c:3788 [inline]
__lock_acquire+0x2c33/0x7c60 kernel/locking/lockdep.c:5012
lock_acquire+0x197/0x3f0 kernel/locking/lockdep.c:5623
down_write+0x38/0x60 kernel/locking/rwsem.c:1551
inode_lock include/linux/fs.h:787 [inline]
chmod_common+0x184/0x3f0 fs/open.c:576
vfs_fchmod fs/open.c:598 [inline]
__do_sys_fchmod fs/open.c:607 [inline]
__se_sys_fchmod fs/open.c:601 [inline]
__x64_sys_fchmod+0xee/0x150 fs/open.c:601
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f7f1bbaf749
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffd023ad9f8 EFLAGS: 00000246 ORIG_RAX: 000000000000005b
RAX: ffffffffffffffda RBX: 00007f7f1be05fa0 RCX: 00007f7f1bbaf749
RDX: 0000000000000000 RSI: 74528231644fc490 RDI: 0000000000000005
RBP: 00007f7f1bc33f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f7f1be05fa0 R14: 00007f7f1be05fa0 R15: 0000000000000002
</TASK>


---
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