[moderation] [ext4?] KCSAN: data-race in inode_cgwb_move_to_attached / iput

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 088d13246a46 Merge tag 'kbuild-fixes-v6.15' of git://git.k..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=140eb6f4580000
kernel config: https://syzkaller.appspot.com/x/.config?x=7bf27d52ff5e6b29
dashboard link: https://syzkaller.appspot.com/bug?extid=a2d54e154af71a59a531
compiler: Debian clang version 20.1.2 (++20250402124445+58df0ef89dd6-1~exp1~20250402004600.97), Debian LLD 20.1.2
CC: [adilger...@dilger.ca linux...@vger.kernel.org linux-...@vger.kernel.org ty...@mit.edu]

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/3fdd9ad35719/disk-088d1324.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/eeee7adc7ff0/vmlinux-088d1324.xz
kernel image: https://storage.googleapis.com/syzbot-assets/5ef8f3d72863/bzImage-088d1324.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+a2d54e...@syzkaller.appspotmail.com

loop7: detected capacity change from 0 to 1024
EXT4-fs: Ignoring removed bh option
==================================================================
BUG: KCSAN: data-race in inode_cgwb_move_to_attached / iput

write to 0xffff8881072636f8 of 4 bytes by task 12236 on cpu 0:
inode_cgwb_move_to_attached+0x9b/0x310 fs/fs-writeback.c:309
requeue_inode fs/fs-writeback.c:-1 [inline]
writeback_sb_inodes+0x6d9/0xa20 fs/fs-writeback.c:2005
__writeback_inodes_wb+0x94/0x1a0 fs/fs-writeback.c:2047
wb_writeback+0x266/0x5c0 fs/fs-writeback.c:2158
wb_check_start_all fs/fs-writeback.c:2284 [inline]
wb_do_writeback fs/fs-writeback.c:2310 [inline]
wb_workfn+0x4c9/0x910 fs/fs-writeback.c:2343
process_one_work kernel/workqueue.c:3238 [inline]
process_scheduled_works+0x4ce/0x9d0 kernel/workqueue.c:3319
worker_thread+0x582/0x770 kernel/workqueue.c:3400
kthread+0x489/0x510 kernel/kthread.c:464
ret_from_fork+0x4b/0x60 arch/x86/kernel/process.c:153
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

read to 0xffff8881072636f8 of 4 bytes by task 24980 on cpu 1:
iput+0x32/0x5b0 fs/inode.c:1914
ext4_xattr_block_set+0x1554/0x1a30 fs/ext4/xattr.c:2001
ext4_xattr_set_handle+0xdc8/0xe70 fs/ext4/xattr.c:2447
ext4_xattr_set+0x18e/0x240 fs/ext4/xattr.c:2549
ext4_xattr_trusted_set+0x3c/0x50 fs/ext4/xattr_trusted.c:38
__vfs_setxattr+0x2e6/0x310 fs/xattr.c:200
__vfs_setxattr_noperm+0xe8/0x410 fs/xattr.c:234
__vfs_setxattr_locked+0x1af/0x1d0 fs/xattr.c:295
vfs_setxattr+0x132/0x270 fs/xattr.c:321
do_setxattr fs/xattr.c:636 [inline]
filename_setxattr+0x1ad/0x400 fs/xattr.c:665
path_setxattrat+0x2c9/0x310 fs/xattr.c:713
__do_sys_setxattr fs/xattr.c:747 [inline]
__se_sys_setxattr fs/xattr.c:743 [inline]
__x64_sys_setxattr+0x6e/0x90 fs/xattr.c:743
x64_sys_call+0x28a7/0x2fb0 arch/x86/include/generated/asm/syscalls_64.h:189
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd0/0x1a0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x00010002 -> 0x00000000

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 24980 Comm: syz.7.6812 Tainted: G W 6.15.0-rc6-syzkaller-00105-g088d13246a46 #0 PREEMPT(voluntary)
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/19/2025
==================================================================


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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.