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

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: ba65a4e7120a Merge tag 'clk-for-linus' of git://git.kernel..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=12fb321a580000
kernel config: https://syzkaller.appspot.com/x/.config?x=c3201432211be40f
dashboard link: https://syzkaller.appspot.com/bug?extid=bfda6b53f6bfa1e0f7fd
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/ab97bb83627b/disk-ba65a4e7.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/3120fbf099f9/vmlinux-ba65a4e7.xz
kernel image: https://storage.googleapis.com/syzbot-assets/54e6d3152e4a/bzImage-ba65a4e7.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+bfda6b...@syzkaller.appspotmail.com

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

write to 0xffff8881044e8f7c of 4 bytes by task 3846 on cpu 1:
inode_set_mtime_to_ts include/linux/fs.h:1658 [inline]
__simple_unlink fs/libfs.c:798 [inline]
simple_unlink+0x54/0x80 fs/libfs.c:814
shmem_unlink+0x12d/0x140 mm/shmem.c:3991
shmem_rename2+0x1a1/0x290 mm/shmem.c:4076
vfs_rename+0x97f/0xad0 fs/namei.c:5929
do_renameat2+0x383/0x810 fs/namei.c:6047
__do_sys_rename fs/namei.c:6090 [inline]
__se_sys_rename fs/namei.c:6088 [inline]
__x64_sys_rename+0x58/0x70 fs/namei.c:6088
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+0xd8/0x2a0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff8881044e8f7c of 4 bytes by task 3511 on cpu 0:
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:1274
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+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+0xd8/0x2a0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x2c520db8 -> 0x2d385f71

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 3511 Comm: udevd Not tainted syzkaller #0 PREEMPT(voluntary)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
==================================================================


---
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