Message-ID: <69483ee2.a70a0220.25eec0.0075.GAE@google.com>
Date: Sun, 21 Dec 2025 10:39:30 -0800
From: syzbot <syzbot+f0b58a1f5075a90dd9a5@...kaller.appspotmail.com>
To: adilger.kernel@...ger.ca, linux-ext4@...r.kernel.org, 
	linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com, tytso@....edu
Subject: Re: [syzbot] [ext4?] possible deadlock in ext4_xattr_set_handle (7)

syzbot has found a reproducer for the following issue on:

HEAD commit:    9094662f6707 Merge tag 'ata-6.19-rc2' of git://git.kernel...
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=17f35b1a580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=1f2b6fe1fdf1a00b
dashboard link: https://syzkaller.appspot.com/bug?extid=f0b58a1f5075a90dd9a5
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=14439392580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=11d7ab1a580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/1fb62303749d/disk-9094662f.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/a4c24905e5fb/vmlinux-9094662f.xz
kernel image: https://storage.googleapis.com/syzbot-assets/791494b6840b/bzImage-9094662f.xz
mounted in repro #1: https://storage.googleapis.com/syzbot-assets/43239235f79e/mount_0.gz
  fsck result: failed (log: https://syzkaller.appspot.com/x/fsck.log?x=10439392580000)
mounted in repro #2: https://storage.googleapis.com/syzbot-assets/5757d87bd66a/mount_1.gz
  fsck result: OK (log: https://syzkaller.appspot.com/x/fsck.log?x=16d7ab1a580000)

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+f0b58a1f5075a90dd9a5@...kaller.appspotmail.com

loop0: detected capacity change from 0 to 128
EXT4-fs (loop0): mounted filesystem 76b65be2-f6da-4727-8c75-0525a5b65a09 r/w without journal. Quota mode: writeback.
ext4 filesystem being mounted at /2/file1 supports timestamps until 2038-01-19 (0x7fffffff)
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.0.19/5970 is trying to acquire lock:
ffff888059addff8 (&ei->xattr_sem){++++}-{4:4}, at: ext4_write_lock_xattr fs/ext4/xattr.h:157 [inline]
ffff888059addff8 (&ei->xattr_sem){++++}-{4:4}, at: ext4_xattr_set_handle+0x165/0x1590 fs/ext4/xattr.c:2371

but task is already holding lock:
ffff888034378c58 (&sbi->s_writepages_rwsem){++++}-{0:0}, at: ext4_writepages_down_write fs/ext4/ext4.h:1832 [inline]
ffff888034378c58 (&sbi->s_writepages_rwsem){++++}-{0:0}, at: ext4_ext_migrate+0x2f3/0x1010 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_internal+0x48/0x1d0 include/linux/percpu-rwsem.h:53
       percpu_down_read include/linux/percpu-rwsem.h:77 [inline]
       ext4_writepages_down_read fs/ext4/ext4.h:1820 [inline]
       ext4_writepages+0x1ca/0x350 fs/ext4/inode.c:3025
       do_writepages+0x32e/0x550 mm/page-writeback.c:2598
       __writeback_single_inode+0x133/0x1240 fs/fs-writeback.c:1737
       writeback_single_inode+0x488/0xd60 fs/fs-writeback.c:1858
       write_inode_now+0x160/0x1d0 fs/fs-writeback.c:2924
       iput_final fs/inode.c:1941 [inline]
       iput+0xa77/0x1030 fs/inode.c:2003
       ext4_xattr_block_set+0x1fce/0x2ac0 fs/ext4/xattr.c:2203
       ext4_xattr_move_to_block fs/ext4/xattr.c:2668 [inline]
       ext4_xattr_make_inode_space fs/ext4/xattr.c:2743 [inline]
       ext4_expand_extra_isize_ea+0x12da/0x1ea0 fs/ext4/xattr.c:2831
       __ext4_expand_extra_isize+0x30d/0x400 fs/ext4/inode.c:6349
       ext4_try_to_expand_extra_isize fs/ext4/inode.c:6392 [inline]
       __ext4_mark_inode_dirty+0x45c/0x6e0 fs/ext4/inode.c:6470
       ext4_evict_inode+0x79c/0xe60 fs/ext4/inode.c:253
       evict+0x5f4/0xae0 fs/inode.c:837
       ext4_orphan_cleanup+0xc20/0x1460 fs/ext4/orphan.c:472
       __ext4_fill_super fs/ext4/super.c:5658 [inline]
       ext4_fill_super+0x58ad/0x6170 fs/ext4/super.c:5777
       get_tree_bdev_flags+0x40e/0x4d0 fs/super.c:1691
       vfs_get_tree+0x92/0x2a0 fs/super.c:1751
       fc_mount fs/namespace.c:1199 [inline]
       do_new_mount_fc fs/namespace.c:3636 [inline]
       do_new_mount+0x302/0xa10 fs/namespace.c:3712
       do_mount fs/namespace.c:4035 [inline]
       __do_sys_mount fs/namespace.c:4224 [inline]
       __se_sys_mount+0x313/0x410 fs/namespace.c:4201
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xec/0xf80 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (&ei->xattr_sem){++++}-{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+0x15a6/0x2cf0 kernel/locking/lockdep.c:5237
       lock_acquire+0x107/0x340 kernel/locking/lockdep.c:5868
       down_write+0x3a/0x50 kernel/locking/rwsem.c:1590
       ext4_write_lock_xattr fs/ext4/xattr.h:157 [inline]
       ext4_xattr_set_handle+0x165/0x1590 fs/ext4/xattr.c:2371
       ext4_initxattrs+0x9f/0x110 fs/ext4/xattr_security.c:44
       security_inode_init_security+0x290/0x3d0 security/security.c:1344
       __ext4_new_inode+0x32f7/0x3c90 fs/ext4/ialloc.c:1324
       ext4_ext_migrate+0x69f/0x1010 fs/ext4/migrate.c:456
       __ext4_ioctl fs/ext4/ioctl.c:1688 [inline]
       ext4_ioctl+0x2053/0x4770 fs/ext4/ioctl.c:1917
       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+0xec/0xf80 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
       ----                    ----
  lock(&sbi->s_writepages_rwsem);
                               lock(&ei->xattr_sem);
                               lock(&sbi->s_writepages_rwsem);
  lock(&ei->xattr_sem);

 *** DEADLOCK ***

3 locks held by syz.0.19/5970:
 #0: ffff88803cf08480 (sb_writers#4){.+.+}-{0:0}, at: mnt_want_write_file+0x63/0x210 fs/namespace.c:543
 #1: ffff888059afb450 (&sb->s_type->i_mutex_key#9){++++}-{4:4}, at: inode_lock include/linux/fs.h:1027 [inline]
 #1: ffff888059afb450 (&sb->s_type->i_mutex_key#9){++++}-{4:4}, at: __ext4_ioctl fs/ext4/ioctl.c:1687 [inline]
 #1: ffff888059afb450 (&sb->s_type->i_mutex_key#9){++++}-{4:4}, at: ext4_ioctl+0x204b/0x4770 fs/ext4/ioctl.c:1917
 #2: ffff888034378c58 (&sbi->s_writepages_rwsem){++++}-{0:0}, at: ext4_writepages_down_write fs/ext4/ext4.h:1832 [inline]
 #2: ffff888034378c58 (&sbi->s_writepages_rwsem){++++}-{0:0}, at: ext4_ext_migrate+0x2f3/0x1010 fs/ext4/migrate.c:438

stack backtrace:
CPU: 1 UID: 0 PID: 5970 Comm: syz.0.19 Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_circular_bug+0x2e2/0x300 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+0x15a6/0x2cf0 kernel/locking/lockdep.c:5237
 lock_acquire+0x107/0x340 kernel/locking/lockdep.c:5868
 down_write+0x3a/0x50 kernel/locking/rwsem.c:1590
 ext4_write_lock_xattr fs/ext4/xattr.h:157 [inline]
 ext4_xattr_set_handle+0x165/0x1590 fs/ext4/xattr.c:2371
 ext4_initxattrs+0x9f/0x110 fs/ext4/xattr_security.c:44
 security_inode_init_security+0x290/0x3d0 security/security.c:1344
 __ext4_new_inode+0x32f7/0x3c90 fs/ext4/ialloc.c:1324
 ext4_ext_migrate+0x69f/0x1010 fs/ext4/migrate.c:456
 __ext4_ioctl fs/ext4/ioctl.c:1688 [inline]
 ext4_ioctl+0x2053/0x4770 fs/ext4/ioctl.c:1917
 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+0xec/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f125b9bf749
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:00007ffc2fb97128 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f125bc15fa0 RCX: 00007f125b9bf749
RDX: 0000000000000000 RSI: 0000000000006609 RDI: 0000000000000005
RBP: 00007f125ba43f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f125bc15fa0 R14: 00007f125bc15fa0 R15: 0000000000000002
 </TASK>


---
If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

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