[v6.6] possible deadlock in ext4_xattr_set_handle

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 3b9f64db0496 Linux 6.6.138
git tree: linux-6.6.y
console output: https://syzkaller.appspot.com/x/log.txt?x=1150776c580000
kernel config: https://syzkaller.appspot.com/x/.config?x=c5b35c4db8465904
dashboard link: https://syzkaller.appspot.com/bug?extid=fccdae14434d56ae4932
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/9e5afbe648d5/disk-3b9f64db.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/c3607dd9b93c/vmlinux-3b9f64db.xz
kernel image: https://storage.googleapis.com/syzbot-assets/f0392d8b3ded/bzImage-3b9f64db.xz

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

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.3.1253/11542 is trying to acquire lock:
ffff88805c5a8ac8 (&ei->xattr_sem){++++}-{3:3}, at: ext4_write_lock_xattr fs/ext4/xattr.h:158 [inline]
ffff88805c5a8ac8 (&ei->xattr_sem){++++}-{3:3}, at: ext4_xattr_set_handle+0x19d/0x14c0 fs/ext4/xattr.c:2367

but task is already holding lock:
ffff88802ff8ac58 (&sbi->s_writepages_rwsem){++++}-{0:0}, at: ext4_writepages_down_write fs/ext4/ext4.h:1780 [inline]
ffff88802ff8ac58 (&sbi->s_writepages_rwsem){++++}-{0:0}, at: ext4_ext_migrate+0x321/0x1080 fs/ext4/migrate.c:438

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (&sbi->s_writepages_rwsem){++++}-{0:0}:
percpu_down_read+0x44/0x1a0 include/linux/percpu-rwsem.h:51
ext4_writepages_down_read fs/ext4/ext4.h:1768 [inline]
ext4_writepages+0x1a4/0x350 fs/ext4/inode.c:2808
do_writepages+0x3b3/0x630 mm/page-writeback.c:2575
__writeback_single_inode+0x153/0xec0 fs/fs-writeback.c:1635
writeback_single_inode+0x21f/0x760 fs/fs-writeback.c:1756
write_inode_now+0x183/0x210 fs/fs-writeback.c:2808
iput_final fs/inode.c:1807 [inline]
iput+0x5ae/0x920 fs/inode.c:1846
ext4_xattr_block_set+0x249e/0x32b0 fs/ext4/xattr.c:2146
ext4_xattr_move_to_block fs/ext4/xattr.c:2664 [inline]
ext4_xattr_make_inode_space fs/ext4/xattr.c:2739 [inline]
ext4_expand_extra_isize_ea+0x12c5/0x1e80 fs/ext4/xattr.c:2827
__ext4_expand_extra_isize+0x306/0x400 fs/ext4/inode.c:5990
ext4_try_to_expand_extra_isize fs/ext4/inode.c:6033 [inline]
__ext4_mark_inode_dirty+0x45d/0x6e0 fs/ext4/inode.c:6111
ext4_evict_inode+0x7f3/0xea0 fs/ext4/inode.c:254
evict+0x4ca/0x8d0 fs/inode.c:705
ext4_orphan_cleanup+0xbec/0x1420 fs/ext4/orphan.c:472
__ext4_fill_super fs/ext4/super.c:5621 [inline]
ext4_fill_super+0x5eea/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

-> #0 (&ei->xattr_sem){++++}-{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
down_write+0x97/0x200 kernel/locking/rwsem.c:1573
ext4_write_lock_xattr fs/ext4/xattr.h:158 [inline]
ext4_xattr_set_handle+0x19d/0x14c0 fs/ext4/xattr.c:2367
ext4_set_context+0x230/0x560 fs/ext4/crypto.c:179
fscrypt_set_context+0x1e6/0x280 fs/crypto/policy.c:761
__ext4_new_inode+0x2eaa/0x3ac0 fs/ext4/ialloc.c:1326
ext4_ext_migrate+0x6f0/0x1080 fs/ext4/migrate.c:456
__ext4_ioctl fs/ext4/ioctl.c:1412 [inline]
ext4_ioctl+0x1ee3/0x3b80 fs/ext4/ioctl.c:1630
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

other info that might help us debug this:

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(&sbi->s_writepages_rwsem);
lock(&ei->xattr_sem);
lock(&sbi->s_writepages_rwsem);
lock(&ei->xattr_sem);

*** DEADLOCK ***

3 locks held by syz.3.1253/11542:
#0: ffff88802ff8c418 (sb_writers#4){++++}-{0:0}, at: mnt_want_write_file+0x63/0x200 fs/namespace.c:456
#1: ffff88805c5a8410 (&sb->s_type->i_mutex_key#9){++++}-{3:3}, at: inode_lock include/linux/fs.h:804 [inline]
#1: ffff88805c5a8410 (&sb->s_type->i_mutex_key#9){++++}-{3:3}, at: __ext4_ioctl fs/ext4/ioctl.c:1411 [inline]
#1: ffff88805c5a8410 (&sb->s_type->i_mutex_key#9){++++}-{3:3}, at: ext4_ioctl+0x1edb/0x3b80 fs/ext4/ioctl.c:1630
#2: ffff88802ff8ac58 (&sbi->s_writepages_rwsem){++++}-{0:0}, at: ext4_writepages_down_write fs/ext4/ext4.h:1780 [inline]
#2: ffff88802ff8ac58 (&sbi->s_writepages_rwsem){++++}-{0:0}, at: ext4_ext_migrate+0x321/0x1080 fs/ext4/migrate.c:438

stack backtrace:
CPU: 1 PID: 11542 Comm: syz.3.1253 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
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
down_write+0x97/0x200 kernel/locking/rwsem.c:1573
ext4_write_lock_xattr fs/ext4/xattr.h:158 [inline]
ext4_xattr_set_handle+0x19d/0x14c0 fs/ext4/xattr.c:2367
ext4_set_context+0x230/0x560 fs/ext4/crypto.c:179
fscrypt_set_context+0x1e6/0x280 fs/crypto/policy.c:761
__ext4_new_inode+0x2eaa/0x3ac0 fs/ext4/ialloc.c:1326
ext4_ext_migrate+0x6f0/0x1080 fs/ext4/migrate.c:456
__ext4_ioctl fs/ext4/ioctl.c:1412 [inline]
ext4_ioctl+0x1ee3/0x3b80 fs/ext4/ioctl.c:1630
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
RIP: 0033:0x7f178999cdd9
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:00007f178a895028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f1789c16090 RCX: 00007f178999cdd9
RDX: 0000000000000000 RSI: 0000000000006609 RDI: 0000000000000004
RBP: 00007f1789a32d69 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f1789c16128 R14: 00007f1789c16090 R15: 00007ffd3ecfd1a8
</TASK>


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