[moderation] [fs?] KCSAN: data-race in fill_mg_cmtime / inode_set_ctime_current (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 63804fed149a Linux 6.19-rc7
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1441205a580000
kernel config: https://syzkaller.appspot.com/x/.config?x=8e27f4588a0f2183
dashboard link: https://syzkaller.appspot.com/bug?extid=6da2951b1409c3ab0d6f
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/a01803567280/disk-63804fed.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/2e8f54c26352/vmlinux-63804fed.xz
kernel image: https://storage.googleapis.com/syzbot-assets/aedebc96acfe/bzImage-63804fed.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+6da295...@syzkaller.appspotmail.com

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

write to 0xffff8881039e7250 of 8 bytes by task 3305 on cpu 0:
inode_set_ctime_current+0x592/0x810 fs/inode.c:2843
shmem_mknod+0x127/0x170 mm/shmem.c:3889
shmem_create+0x34/0x50 mm/shmem.c:3943
lookup_open fs/namei.c:4449 [inline]
open_last_lookups fs/namei.c:4549 [inline]
path_openat+0x1121/0x23c0 fs/namei.c:4793
do_filp_open+0x15d/0x280 fs/namei.c:4823
do_sys_openat2+0xa6/0x150 fs/open.c:1430
do_sys_open fs/open.c:1436 [inline]
__do_sys_openat fs/open.c:1452 [inline]
__se_sys_openat fs/open.c:1447 [inline]
__x64_sys_openat+0xf2/0x120 fs/open.c:1447
x64_sys_call+0x2b07/0x3000 arch/x86/include/generated/asm/syscalls_64.h:258
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 0xffff8881039e7250 of 8 bytes by task 3306 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:1274
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: 0x00000000773d97c1 -> 0x00000000773d97c2

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 3306 Comm: udevd Tainted: G W syzkaller #0 PREEMPT(voluntary)
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
==================================================================


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