[moderation] [fs?] KCSAN: data-race in fill_mg_cmtime / inode_set_ctime_current

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: d2818517e348 Merge tag 'block-6.18-20251023' of git://git...
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=10a85d2f980000
kernel config: https://syzkaller.appspot.com/x/.config?x=15383e23338541bf
dashboard link: https://syzkaller.appspot.com/bug?extid=e3b8520e31d493bb1db2
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
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/d791cec879a5/disk-d2818517.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/6f98cca822a8/vmlinux-d2818517.xz
kernel image: https://storage.googleapis.com/syzbot-assets/70c5b94e1084/bzImage-d2818517.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+e3b852...@syzkaller.appspotmail.com

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

write to 0xffff888103862c80 of 8 bytes by task 19941 on cpu 0:
inode_set_ctime_current+0x533/0x770 fs/inode.c:2810
shmem_mknod+0x11b/0x180 mm/shmem.c:3858
shmem_create+0x34/0x50 mm/shmem.c:3917
lookup_open fs/namei.c:3796 [inline]
open_last_lookups fs/namei.c:3895 [inline]
path_openat+0x1105/0x2170 fs/namei.c:4131
do_filp_open+0x109/0x230 fs/namei.c:4161
do_sys_openat2+0xa6/0x110 fs/open.c:1437
do_sys_open fs/open.c:1452 [inline]
__do_sys_openat fs/open.c:1468 [inline]
__se_sys_openat fs/open.c:1463 [inline]
__x64_sys_openat+0xf2/0x120 fs/open.c:1463
x64_sys_call+0x2eab/0x3000 arch/x86/include/generated/asm/syscalls_64.h:258
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd2/0x200 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff888103862c80 of 8 bytes by task 19943 on cpu 1:
fill_mg_cmtime+0x86/0x260 fs/stat.c:56
generic_fillattr+0x24a/0x340 fs/stat.c:99
shmem_getattr+0x181/0x200 mm/shmem.c:1257
vfs_getattr_nosec+0x146/0x1e0 fs/stat.c:213
vfs_getattr fs/stat.c:262 [inline]
vfs_statx_path fs/stat.c:299 [inline]
vfs_statx+0x113/0x390 fs/stat.c:356
vfs_fstatat+0x115/0x170 fs/stat.c:375
__do_sys_newfstatat fs/stat.c:542 [inline]
__se_sys_newfstatat+0x55/0x260 fs/stat.c:536
__x64_sys_newfstatat+0x55/0x70 fs/stat.c:536
x64_sys_call+0x135a/0x3000 arch/x86/include/generated/asm/syscalls_64.h:263
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd2/0x200 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x0000000068fc3d6f -> 0x0000000068fc3d71

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 19943 Comm: udevd Not tainted syzkaller #0 PREEMPT(voluntary)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
==================================================================


---
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