[syzbot] [ext4?] possible deadlock in ext4_map_blocks (3)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 66182ca873a4 Merge tag 'net-7.1-rc4' of git://git.kernel.o..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=10328d6a580000
kernel config: https://syzkaller.appspot.com/x/.config?x=f2e8ebfec4636d32
dashboard link: https://syzkaller.appspot.com/bug?extid=1d62d734f435d85cc693
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/04f707fb980e/disk-66182ca8.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/88110d832473/vmlinux-66182ca8.xz
kernel image: https://storage.googleapis.com/syzbot-assets/fd09a1619478/bzImage-66182ca8.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+1d62d7...@syzkaller.appspotmail.com

============================================
WARNING: possible recursive locking detected
syzkaller #0 Not tainted
--------------------------------------------
syz.4.1400/19208 is trying to acquire lock:
ffff888040b26cd0 (&ei->i_data_sem/2){++++}-{4:4}, at: ext4_map_blocks+0x7b5/0x11d0 fs/ext4/inode.c:823

but task is already holding lock:
ffff888040b231c0 (&ei->i_data_sem/2){++++}-{4:4}, at: ext4_map_blocks+0x7b5/0x11d0 fs/ext4/inode.c:823

other info that might help us debug this:
Possible unsafe locking scenario:

CPU0
----
lock(&ei->i_data_sem/2);
lock(&ei->i_data_sem/2);

*** DEADLOCK ***

May be due to missing lock nesting notation

6 locks held by syz.4.1400/19208:
#0: ffff888025696480 (sb_writers#4){.+.+}-{0:0}, at: file_start_write include/linux/fs.h:2724 [inline]
#0: ffff888025696480 (sb_writers#4){.+.+}-{0:0}, at: vfs_write+0x22d/0xba0 fs/read_write.c:684
#1: ffff888040b23360 (&sb->s_type->i_mutex_key#10){++++}-{4:4}, at: inode_lock include/linux/fs.h:1029 [inline]
#1: ffff888040b23360 (&sb->s_type->i_mutex_key#10){++++}-{4:4}, at: ext4_buffered_write_iter+0xa1/0x3a0 fs/ext4/file.c:311
#2: ffff888040b231c0 (&ei->i_data_sem/2){++++}-{4:4}, at: ext4_map_blocks+0x7b5/0x11d0 fs/ext4/inode.c:823
#3: ffffffff8e170dd8 (dquot_srcu){.+.+}-{0:0}, at: srcu_lock_acquire include/linux/srcu.h:187 [inline]
#3: ffffffff8e170dd8 (dquot_srcu){.+.+}-{0:0}, at: srcu_read_lock include/linux/srcu.h:294 [inline]
#3: ffffffff8e170dd8 (dquot_srcu){.+.+}-{0:0}, at: __dquot_alloc_space+0x18d/0xea0 fs/quota/dquot.c:1729
#4: ffff888062ce2a98 (&dquot->dq_lock){+.+.}-{4:4}, at: dquot_commit+0x5e/0x450 fs/quota/dquot.c:533
#5: ffff8880256961e8 (&s->s_dquot.dqio_sem){++++}-{4:4}, at: v2_write_dquot+0x9c/0x260 fs/quota/quota_v2.c:369

stack backtrace:
CPU: 1 UID: 0 PID: 19208 Comm: syz.4.1400 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_deadlock_bug+0x279/0x290 kernel/locking/lockdep.c:3041
check_deadlock kernel/locking/lockdep.c:3093 [inline]
validate_chain kernel/locking/lockdep.c:3895 [inline]
__lock_acquire+0x253f/0x2cf0 kernel/locking/lockdep.c:5237
lock_acquire+0x106/0x350 kernel/locking/lockdep.c:5868
down_write+0x3a/0x50 kernel/locking/rwsem.c:1625
ext4_map_blocks+0x7b5/0x11d0 fs/ext4/inode.c:823
ext4_getblk+0x1ca/0x780 fs/ext4/inode.c:992
ext4_bread+0x2a/0x180 fs/ext4/inode.c:1055
ext4_quota_write+0x239/0x580 fs/ext4/super.c:7398
qtree_write_dquot+0x25b/0x5e0 fs/quota/quota_tree.c:462
v2_write_dquot+0x183/0x260 fs/quota/quota_v2.c:372
dquot_commit+0x377/0x450 fs/quota/dquot.c:540
ext4_write_dquot+0x20a/0x380 fs/ext4/super.c:7010
mark_dquot_dirty fs/quota/dquot.c:398 [inline]
mark_all_dquot_dirty+0x205/0x460 fs/quota/dquot.c:438
__dquot_alloc_space+0x620/0xea0 fs/quota/dquot.c:1765
dquot_alloc_space_nodirty include/linux/quotaops.h:292 [inline]
dquot_alloc_space include/linux/quotaops.h:305 [inline]
dquot_alloc_block include/linux/quotaops.h:329 [inline]
ext4_mb_new_blocks+0xfb1/0x46d0 fs/ext4/mballoc.c:6276
ext4_ext_map_blocks+0x1515/0x5860 fs/ext4/extents.c:4461
ext4_map_create_blocks+0x11d/0x540 fs/ext4/inode.c:631
ext4_map_blocks+0x7cd/0x11d0 fs/ext4/inode.c:824
_ext4_get_block+0x1e3/0x470 fs/ext4/inode.c:924
ext4_get_block_unwritten+0x2e/0x100 fs/ext4/inode.c:957
ext4_block_write_begin+0xb14/0x1950 fs/ext4/inode.c:1211
ext4_write_begin+0xb40/0x1890 fs/ext4/ext4_jbd2.h:-1
ext4_da_write_begin+0x355/0xd60 fs/ext4/inode.c:3152
generic_perform_write+0x2af/0x8b0 mm/filemap.c:4325
ext4_buffered_write_iter+0xd0/0x3a0 fs/ext4/file.c:316
ext4_file_write_iter+0x299/0x1c10 fs/ext4/file.c:-1
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+0x15f/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f50b506ce59
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:00007f50b32be028 EFLAGS: 00000246 ORIG_RAX: 0000000000000012
RAX: ffffffffffffffda RBX: 00007f50b52e5fa0 RCX: 00007f50b506ce59
RDX: 0000000000000001 RSI: 0000200000000140 RDI: 0000000000000007
RBP: 00007f50b5102d6f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000008080c61 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f50b52e6038 R14: 00007f50b52e5fa0 R15: 00007fff20f29238
</TASK>


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