[v6.1] possible deadlock in ext4_move_extents (4)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 8ce36b2849ef Linux 6.1.163
git tree: linux-6.1.y
console output: https://syzkaller.appspot.com/x/log.txt?x=129c07b2580000
kernel config: https://syzkaller.appspot.com/x/.config?x=f0605c5af04d7603
dashboard link: https://syzkaller.appspot.com/bug?extid=92513c0a92550288956d
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/25d3bb1313db/disk-8ce36b28.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/53d3c77e16da/vmlinux-8ce36b28.xz
kernel image: https://storage.googleapis.com/syzbot-assets/ca171a78e481/bzImage-8ce36b28.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+92513c...@syzkaller.appspotmail.com

ext4 filesystem being mounted at /141/bus supports timestamps until 2038-01-19 (0x7fffffff)
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.9.3449/16157 is trying to acquire lock:
ffff888070895cd0 (&ei->i_data_sem/1){+.+.}-{3:3}, at: ext4_move_extents+0x331/0xbb0 fs/ext4/move_extent.c:615

but task is already holding lock:
ffff88805529a0a0 (&ei->i_data_sem/2){++++}-{3:3}, at: ext4_double_down_write_data_sem+0x28/0x40 fs/ext4/move_extent.c:-1

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #3 (&ei->i_data_sem/2){++++}-{3:3}:
down_read+0x42/0x2d0 kernel/locking/rwsem.c:1520
ext4_map_blocks+0x323/0x1b70 fs/ext4/inode.c:604
ext4_getblk+0x1cc/0x6f0 fs/ext4/inode.c:890
ext4_bread+0x26/0x170 fs/ext4/inode.c:946
ext4_quota_read+0x180/0x380 fs/ext4/super.c:7176
read_blk fs/quota/quota_tree.c:61 [inline]
find_tree_dqentry+0x1cd/0xf30 fs/quota/quota_tree.c:671
find_tree_dqentry+0x6b0/0xf30 fs/quota/quota_tree.c:698
find_tree_dqentry+0x6b0/0xf30 fs/quota/quota_tree.c:698
find_tree_dqentry+0x6b0/0xf30 fs/quota/quota_tree.c:698
find_dqentry fs/quota/quota_tree.c:716 [inline]
qtree_read_dquot+0x57b/0x820 fs/quota/quota_tree.c:736
v2_read_dquot+0xc0/0x110 fs/quota/quota_v2.c:336
dquot_acquire+0x152/0x520 fs/quota/dquot.c:463
ext4_acquire_dquot+0x2d9/0x4a0 fs/ext4/super.c:6831
dqget+0x778/0xeb0 fs/quota/dquot.c:988
__dquot_initialize+0x333/0xcd0 fs/quota/dquot.c:1517
ext4_process_orphan+0x54/0x300 fs/ext4/orphan.c:327
ext4_orphan_cleanup+0xbeb/0x1420 fs/ext4/orphan.c:472
__ext4_fill_super fs/ext4/super.c:5556 [inline]
ext4_fill_super+0x7829/0x7dc0 fs/ext4/super.c:5687
get_tree_bdev+0x3f1/0x610 fs/super.c:1366
vfs_get_tree+0x88/0x270 fs/super.c:1573
do_new_mount+0x24a/0xa40 fs/namespace.c:3078
do_mount fs/namespace.c:3421 [inline]
__do_sys_mount fs/namespace.c:3629 [inline]
__se_sys_mount+0x2e3/0x3d0 fs/namespace.c:3606
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

-> #2 (&s->s_dquot.dqio_sem){++++}-{3:3}:
down_read+0x42/0x2d0 kernel/locking/rwsem.c:1520
v2_read_dquot+0x4a/0x110 fs/quota/quota_v2.c:335
dquot_acquire+0x152/0x520 fs/quota/dquot.c:463
ext4_acquire_dquot+0x2d9/0x4a0 fs/ext4/super.c:6831
dqget+0x778/0xeb0 fs/quota/dquot.c:988
__dquot_initialize+0x3c3/0xcd0 fs/quota/dquot.c:1517
ext4_process_orphan+0x54/0x300 fs/ext4/orphan.c:327
ext4_orphan_cleanup+0xbeb/0x1420 fs/ext4/orphan.c:472
__ext4_fill_super fs/ext4/super.c:5556 [inline]
ext4_fill_super+0x7829/0x7dc0 fs/ext4/super.c:5687
get_tree_bdev+0x3f1/0x610 fs/super.c:1366
vfs_get_tree+0x88/0x270 fs/super.c:1573
do_new_mount+0x24a/0xa40 fs/namespace.c:3078
do_mount fs/namespace.c:3421 [inline]
__do_sys_mount fs/namespace.c:3629 [inline]
__se_sys_mount+0x2e3/0x3d0 fs/namespace.c:3606
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 (&dquot->dq_lock){+.+.}-{3:3}:
__mutex_lock_common kernel/locking/mutex.c:603 [inline]
__mutex_lock+0x12d/0xaf0 kernel/locking/mutex.c:747
dquot_commit+0x5a/0x410 fs/quota/dquot.c:507
ext4_write_dquot+0x1f0/0x360 fs/ext4/super.c:6811
mark_dquot_dirty fs/quota/dquot.c:372 [inline]
mark_all_dquot_dirty+0x1e3/0x400 fs/quota/dquot.c:412
__dquot_alloc_space+0x5fc/0xe60 fs/quota/dquot.c:1752
dquot_alloc_space_nodirty include/linux/quotaops.h:300 [inline]
dquot_alloc_space include/linux/quotaops.h:313 [inline]
dquot_alloc_block include/linux/quotaops.h:337 [inline]
ext4_mb_new_blocks+0xf8d/0x4760 fs/ext4/mballoc.c:5738
ext4_new_meta_blocks+0x172/0x3d0 fs/ext4/balloc.c:739
ext4_ext_grow_indepth fs/ext4/extents.c:1331 [inline]
ext4_ext_create_new_leaf fs/ext4/extents.c:1437 [inline]
ext4_ext_insert_extent+0x1052/0x4810 fs/ext4/extents.c:2105
ext4_split_extent_at+0x7b3/0xf60 fs/ext4/extents.c:3236
ext4_force_split_extent_at fs/ext4/extents.c:338 [inline]
ext4_swap_extents+0x1172/0x1d60 fs/ext4/extents.c:5773
move_extent_per_page+0x1fba/0x4880 fs/ext4/move_extent.c:367
ext4_move_extents+0x8b5/0xbb0 fs/ext4/move_extent.c:678
__ext4_ioctl fs/ext4/ioctl.c:1358 [inline]
ext4_ioctl+0x37aa/0x4110 fs/ext4/ioctl.c:1614
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

-> #0 (&ei->i_data_sem/1){+.+.}-{3:3}:
check_prev_add kernel/locking/lockdep.c:3090 [inline]
check_prevs_add kernel/locking/lockdep.c:3209 [inline]
validate_chain kernel/locking/lockdep.c:3825 [inline]
__lock_acquire+0x2d07/0x7d10 kernel/locking/lockdep.c:5049
lock_acquire+0x1bb/0x4a0 kernel/locking/lockdep.c:5662
down_write_nested+0x39/0x60 kernel/locking/rwsem.c:1689
ext4_move_extents+0x331/0xbb0 fs/ext4/move_extent.c:615
__ext4_ioctl fs/ext4/ioctl.c:1358 [inline]
ext4_ioctl+0x37aa/0x4110 fs/ext4/ioctl.c:1614
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

other info that might help us debug this:

Chain exists of:
&ei->i_data_sem/1 --> &s->s_dquot.dqio_sem --> &ei->i_data_sem/2

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(&ei->i_data_sem/2);
lock(&s->s_dquot.dqio_sem);
lock(&ei->i_data_sem/2);
lock(&ei->i_data_sem/1);

*** DEADLOCK ***

4 locks held by syz.9.3449/16157:
#0: ffff8880788a8460 (sb_writers#4){.+.+}-{0:0}, at: mnt_want_write_file+0x5c/0x200 fs/namespace.c:446
#1: ffff88805529a218 (&sb->s_type->i_mutex_key#9){++++}-{3:3}, at: inode_lock include/linux/fs.h:758 [inline]
#1: ffff88805529a218 (&sb->s_type->i_mutex_key#9){++++}-{3:3}, at: lock_two_nondirectories+0xd5/0x150 fs/inode.c:1208
#2: ffff888070895e48 (&sb->s_type->i_mutex_key#9/4){+.+.}-{3:3}, at: ext4_move_extents+0x316/0xbb0 fs/ext4/move_extent.c:608
#3: ffff88805529a0a0 (&ei->i_data_sem/2){++++}-{3:3}, at: ext4_double_down_write_data_sem+0x28/0x40 fs/ext4/move_extent.c:-1

stack backtrace:
CPU: 1 PID: 16157 Comm: syz.9.3449 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
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:3090 [inline]
check_prevs_add kernel/locking/lockdep.c:3209 [inline]
validate_chain kernel/locking/lockdep.c:3825 [inline]
__lock_acquire+0x2d07/0x7d10 kernel/locking/lockdep.c:5049
lock_acquire+0x1bb/0x4a0 kernel/locking/lockdep.c:5662
down_write_nested+0x39/0x60 kernel/locking/rwsem.c:1689
ext4_move_extents+0x331/0xbb0 fs/ext4/move_extent.c:615
__ext4_ioctl fs/ext4/ioctl.c:1358 [inline]
ext4_ioctl+0x37aa/0x4110 fs/ext4/ioctl.c:1614
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
RIP: 0033:0x7f592e79c629
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:00007f592c9f6028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f592ea15fa0 RCX: 00007f592e79c629
RDX: 0000200000000040 RSI: 00000000c028660f RDI: 0000000000000005
RBP: 00007f592e832b39 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f592ea16038 R14: 00007f592ea15fa0 R15: 00007fff07409948
</TASK>


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