[syzbot] [overlayfs?] [ext4?] possible deadlock in lock_two_nondirectories (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: ba3e43a9e601 Merge tag 'soc-fixes-7.1-2' of git://git.kern..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1033aa56580000
kernel config: https://syzkaller.appspot.com/x/.config?x=bd38685893011045
dashboard link: https://syzkaller.appspot.com/bug?extid=ad6118a7584b607c67f2
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=17e2f3ec580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=174c2a66580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/8759ddf1bfa7/disk-ba3e43a9.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/e2f0e563c705/vmlinux-ba3e43a9.xz
kernel image: https://storage.googleapis.com/syzbot-assets/b40bdb37a0d7/bzImage-ba3e43a9.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/4074e1f6d9f8/mount_0.gz
fsck result: failed (log: https://syzkaller.appspot.com/x/fsck.log?x=1103db7e580000)

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+ad6118...@syzkaller.appspotmail.com

EXT4-fs: Ignoring removed bh option
EXT4-fs (loop0): stripe (5) is not aligned with cluster size (16), stripe is disabled
EXT4-fs (loop0): mounted filesystem 00000000-0000-0000-0000-000000000000 r/w without journal. Quota mode: none.
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.0.22/5968 is trying to acquire lock:
ffff88805aab44a0 (&ovl_i_mutex_key[depth]){+.+.}-{4:4}, at: inode_lock include/linux/fs.h:1029 [inline]
ffff88805aab44a0 (&ovl_i_mutex_key[depth]){+.+.}-{4:4}, at: lock_two_nondirectories+0xe7/0x180 fs/inode.c:1254

but task is already holding lock:
ffff88803ea9c480 (sb_writers#4){.+.+}-{0:0}, at: mnt_want_write_file+0x63/0x210 fs/namespace.c:537

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (sb_writers#4){.+.+}-{0:0}:
percpu_down_read_internal include/linux/percpu-rwsem.h:53 [inline]
percpu_down_read_freezable include/linux/percpu-rwsem.h:83 [inline]
__sb_start_write include/linux/fs/super.h:19 [inline]
sb_start_write+0x4d/0x1c0 include/linux/fs/super.h:125
file_start_write include/linux/fs.h:2724 [inline]
vfs_iter_write+0x1f8/0x610 fs/read_write.c:982
do_backing_file_write_iter fs/backing-file.c:226 [inline]
backing_file_write_iter+0x5e7/0x950 fs/backing-file.c:274
ovl_write_iter+0x2fd/0x3d0 fs/overlayfs/file.c:370
new_sync_write fs/read_write.c:595 [inline]
vfs_write+0x629/0xba0 fs/read_write.c:688
ksys_pwrite64 fs/read_write.c:795 [inline]
__do_sys_pwrite64 fs/read_write.c:803 [inline]
__se_sys_pwrite64 fs/read_write.c:800 [inline]
__x64_sys_pwrite64+0x19c/0x230 fs/read_write.c:800
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (&ovl_i_mutex_key[depth]){+.+.}-{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+0x15a5/0x2cf0 kernel/locking/lockdep.c:5237
lock_acquire+0x106/0x350 kernel/locking/lockdep.c:5868
down_write+0x3a/0x50 kernel/locking/rwsem.c:1625
inode_lock include/linux/fs.h:1029 [inline]
lock_two_nondirectories+0xe7/0x180 fs/inode.c:1254
ext4_move_extents+0x20f/0x3950 fs/ext4/move_extent.c:589
__ext4_ioctl fs/ext4/ioctl.c:1657 [inline]
ext4_ioctl+0x3092/0x4b40 fs/ext4/ioctl.c:1922
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:597 [inline]
__se_sys_ioctl+0xff/0x170 fs/ioctl.c:583
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
rlock(sb_writers#4);
lock(&ovl_i_mutex_key[depth]);
lock(sb_writers#4);
lock(&ovl_i_mutex_key[depth]);

*** DEADLOCK ***

1 lock held by syz.0.22/5968:
#0: ffff88803ea9c480 (sb_writers#4){.+.+}-{0:0}, at: mnt_want_write_file+0x63/0x210 fs/namespace.c:537

stack backtrace:
CPU: 0 UID: 0 PID: 5968 Comm: syz.0.22 Not tainted syzkaller #0 PREEMPT_{RT,(full)}
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
Call Trace:
<TASK>
dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
print_circular_bug+0x2e1/0x300 kernel/locking/lockdep.c:2043
check_noncircular+0x12e/0x150 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+0x15a5/0x2cf0 kernel/locking/lockdep.c:5237
lock_acquire+0x106/0x350 kernel/locking/lockdep.c:5868
down_write+0x3a/0x50 kernel/locking/rwsem.c:1625
inode_lock include/linux/fs.h:1029 [inline]
lock_two_nondirectories+0xe7/0x180 fs/inode.c:1254
ext4_move_extents+0x20f/0x3950 fs/ext4/move_extent.c:589
__ext4_ioctl fs/ext4/ioctl.c:1657 [inline]
ext4_ioctl+0x3092/0x4b40 fs/ext4/ioctl.c:1922
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:597 [inline]
__se_sys_ioctl+0xff/0x170 fs/ioctl.c:583
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fb592a3ce59
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffc3443e838 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fb592cb5fa0 RCX: 00007fb592a3ce59
RDX: 0000200000000040 RSI: 00000000c028660f RDI: 0000000000000005
RBP: 00007fb592ad2d6f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fb592cb5fac R14: 00007fb592cb5fa0 R15: 00007fb592cb5fa0
</TASK>


---
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