Message-ID: <690f466b.a70a0220.22f260.0081.GAE@google.com>
Date: Sat, 08 Nov 2025 05:32:27 -0800
From: syzbot <syzbot+5b61c1d24f8022b26f7d@...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: [syzbot] [ext4?] possible deadlock in ext4_xattr_get (2)

Hello,

syzbot found the following issue on:

HEAD commit:    8bb886cb8f3a Merge tag 'edac_urgent_for_v6.18_rc5' of git:..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=11ea2532580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=e46b8a1c645465a9
dashboard link: https://syzkaller.appspot.com/bug?extid=5b61c1d24f8022b26f7d
compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/addfade563b0/disk-8bb886cb.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/1254c89ad16b/vmlinux-8bb886cb.xz
kernel image: https://storage.googleapis.com/syzbot-assets/3123c5319b7e/bzImage-8bb886cb.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+5b61c1d24f8022b26f7d@...kaller.appspotmail.com

ext4 filesystem being mounted at /86/bus supports timestamps until 2038-01-19 (0x7fffffff)
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.5.1778/13399 is trying to acquire lock:
ffff888047d9ba28 (&ei->xattr_sem){++++}-{4:4}, at: ext4_xattr_get+0x10a/0x6a0 fs/ext4/xattr.c:708

but task is already holding lock:
ffff88807a168b98 (&sbi->s_writepages_rwsem){++++}-{0:0}, at: ext4_writepages_down_write fs/ext4/ext4.h:1808 [inline]
ffff88807a168b98 (&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}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
       percpu_down_read_internal+0x48/0x1c0 include/linux/percpu-rwsem.h:53
       percpu_down_read include/linux/percpu-rwsem.h:77 [inline]
       ext4_writepages_down_read fs/ext4/ext4.h:1796 [inline]
       ext4_writepages+0x1cc/0x350 fs/ext4/inode.c:3024
       do_writepages+0x32e/0x550 mm/page-writeback.c:2604
       __writeback_single_inode+0x145/0xff0 fs/fs-writeback.c:1719
       writeback_single_inode+0x1f9/0x6a0 fs/fs-writeback.c:1840
       write_inode_now+0x160/0x1d0 fs/fs-writeback.c:2903
       iput_final fs/inode.c:1901 [inline]
       iput+0x830/0xc50 fs/inode.c:1966
       ext4_xattr_block_set+0x1fce/0x2ac0 fs/ext4/xattr.c:2199
       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+0x12da/0x1ea0 fs/ext4/xattr.c:2827
       __ext4_expand_extra_isize+0x30d/0x400 fs/ext4/inode.c:6364
       ext4_try_to_expand_extra_isize fs/ext4/inode.c:6407 [inline]
       __ext4_mark_inode_dirty+0x46c/0x700 fs/ext4/inode.c:6485
       ext4_evict_inode+0x80d/0xee0 fs/ext4/inode.c:254
       evict+0x504/0x9c0 fs/inode.c:810
       ext4_orphan_cleanup+0xc20/0x1460 fs/ext4/orphan.c:470
       __ext4_fill_super fs/ext4/super.c:5617 [inline]
       ext4_fill_super+0x5920/0x61e0 fs/ext4/super.c:5736
       get_tree_bdev_flags+0x40e/0x4d0 fs/super.c:1691
       vfs_get_tree+0x92/0x2b0 fs/super.c:1751
       fc_mount fs/namespace.c:1208 [inline]
       do_new_mount_fc fs/namespace.c:3651 [inline]
       do_new_mount+0x302/0xa10 fs/namespace.c:3727
       do_mount fs/namespace.c:4050 [inline]
       __do_sys_mount fs/namespace.c:4238 [inline]
       __se_sys_mount+0x313/0x410 fs/namespace.c:4215
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0xfa0 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+0xb9b/0x2140 kernel/locking/lockdep.c:3908
       __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5237
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
       down_read+0x46/0x2e0 kernel/locking/rwsem.c:1537
       ext4_xattr_get+0x10a/0x6a0 fs/ext4/xattr.c:708
       ext4_get_acl+0x84/0x930 fs/ext4/acl.c:165
       __get_acl+0x279/0x400 fs/posix_acl.c:159
       get_inode_acl fs/posix_acl.c:184 [inline]
       posix_acl_create+0x131/0x440 fs/posix_acl.c:646
       ext4_init_acl+0xb3/0x320 fs/ext4/acl.c:284
       __ext4_new_inode+0x3218/0x3cb0 fs/ext4/ialloc.c:1321
       ext4_ext_migrate+0x69f/0x1010 fs/ext4/migrate.c:456
       __ext4_ioctl fs/ext4/ioctl.c:1694 [inline]
       ext4_ioctl+0x204b/0x48e0 fs/ext4/ioctl.c:1923
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:597 [inline]
       __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0xfa0 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);
  rlock(&ei->xattr_sem);

 *** DEADLOCK ***

3 locks held by syz.5.1778/13399:
 #0: ffff88807a16a420 (sb_writers#4){.+.+}-{0:0}, at: mnt_want_write_file+0x60/0x200 fs/namespace.c:552
 #1: ffff888047d9c6d0 (&sb->s_type->i_mutex_key#9){++++}-{4:4}, at: inode_lock include/linux/fs.h:980 [inline]
 #1: ffff888047d9c6d0 (&sb->s_type->i_mutex_key#9){++++}-{4:4}, at: __ext4_ioctl fs/ext4/ioctl.c:1693 [inline]
 #1: ffff888047d9c6d0 (&sb->s_type->i_mutex_key#9){++++}-{4:4}, at: ext4_ioctl+0x2043/0x48e0 fs/ext4/ioctl.c:1923
 #2: ffff88807a168b98 (&sbi->s_writepages_rwsem){++++}-{0:0}, at: ext4_writepages_down_write fs/ext4/ext4.h:1808 [inline]
 #2: ffff88807a168b98 (&sbi->s_writepages_rwsem){++++}-{0:0}, at: ext4_ext_migrate+0x2f3/0x1010 fs/ext4/migrate.c:438

stack backtrace:
CPU: 0 UID: 0 PID: 13399 Comm: syz.5.1778 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 print_circular_bug+0x2ee/0x310 kernel/locking/lockdep.c:2043
 check_noncircular+0x134/0x160 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+0xb9b/0x2140 kernel/locking/lockdep.c:3908
 __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5237
 lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
 down_read+0x46/0x2e0 kernel/locking/rwsem.c:1537
 ext4_xattr_get+0x10a/0x6a0 fs/ext4/xattr.c:708
 ext4_get_acl+0x84/0x930 fs/ext4/acl.c:165
 __get_acl+0x279/0x400 fs/posix_acl.c:159
 get_inode_acl fs/posix_acl.c:184 [inline]
 posix_acl_create+0x131/0x440 fs/posix_acl.c:646
 ext4_init_acl+0xb3/0x320 fs/ext4/acl.c:284
 __ext4_new_inode+0x3218/0x3cb0 fs/ext4/ialloc.c:1321
 ext4_ext_migrate+0x69f/0x1010 fs/ext4/migrate.c:456
 __ext4_ioctl fs/ext4/ioctl.c:1694 [inline]
 ext4_ioctl+0x204b/0x48e0 fs/ext4/ioctl.c:1923
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f33aa18f6c9
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:00007f33ab026038 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f33aa3e5fa0 RCX: 00007f33aa18f6c9
RDX: 0000000000000000 RSI: 0000000000006609 RDI: 0000000000000006
RBP: 00007f33aa211f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f33aa3e6038 R14: 00007f33aa3e5fa0 R15: 00007ffcf65b20e8
 </TASK>
EXT4-fs error (device loop5): ext4_lookup:1787: inode #12: comm syz.5.1778: iget: bad i_size value: 2533274857506816
EXT4-fs error (device loop5): ext4_lookup:1787: inode #12: comm syz.5.1778: iget: bad i_size value: 2533274857506816


---
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