[moderation] [fs?] KCSAN: data-race in fill_mg_cmtime / simple_rename_timestamp (4)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 05f7e89ab973 Linux 6.19
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15fed402580000
kernel config: https://syzkaller.appspot.com/x/.config?x=8e27f4588a0f2183
dashboard link: https://syzkaller.appspot.com/bug?extid=bff6b8c0851d9be8c736
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
CC: [bra...@kernel.org ja...@suse.cz linux-...@vger.kernel.org linux-...@vger.kernel.org vi...@zeniv.linux.org.uk]

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/bb848ac8f95b/disk-05f7e89a.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/aae899d0a2ce/vmlinux-05f7e89a.xz
kernel image: https://storage.googleapis.com/syzbot-assets/e8b66ec5250e/bzImage-05f7e89a.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+bff6b8...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in fill_mg_cmtime / simple_rename_timestamp

write to 0xffff8881064183dc of 4 bytes by task 3348 on cpu 0:
inode_set_mtime_to_ts include/linux/fs.h:1658 [inline]
simple_rename_timestamp+0x53/0xd0 fs/libfs.c:839
shmem_rename2+0x2df/0x310 mm/shmem.c:4112
vfs_rename+0xa9e/0xbf0 fs/namei.c:5938
do_renameat2+0x39a/0x850 fs/namei.c:6056
__do_sys_rename fs/namei.c:6099 [inline]
__se_sys_rename fs/namei.c:6097 [inline]
__x64_sys_rename+0x58/0x70 fs/namei.c:6097
x64_sys_call+0x24e/0x3000 arch/x86/include/generated/asm/syscalls_64.h:83
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xc0/0x2a0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff8881064183dc of 4 bytes by task 3302 on cpu 1:
inode_get_mtime_nsec include/linux/fs.h:1644 [inline]
inode_get_mtime include/linux/fs.h:1650 [inline]
fill_mg_cmtime+0x5b/0x260 fs/stat.c:55
generic_fillattr+0x24a/0x340 fs/stat.c:99
shmem_getattr+0x181/0x200 mm/shmem.c:1302
vfs_getattr_nosec+0x146/0x1e0 fs/stat.c:213
vfs_getattr+0x48/0x60 fs/stat.c:262
vfs_statx_path+0x28/0x140 fs/stat.c:299
vfs_statx+0xc4/0x170 fs/stat.c:356
vfs_fstatat+0x115/0x170 fs/stat.c:375
__do_sys_newfstatat fs/stat.c:542 [inline]
__se_sys_newfstatat+0x55/0x3e0 fs/stat.c:536
__x64_sys_newfstatat+0x55/0x70 fs/stat.c:536
x64_sys_call+0x111f/0x3000 arch/x86/include/generated/asm/syscalls_64.h:263
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xc0/0x2a0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x3060ea45 -> 0x3062eccd

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 3302 Comm: udevd Tainted: G W syzkaller #0 PREEMPT(voluntary)
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/24/2026
==================================================================


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup