[moderation] [fs?] KCSAN: data-race in generic_fillattr / inode_update_time

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 26fd6bff2c05 Merge tag 'mtd/fixes-for-7.1-rc2' of git://gi..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16c1bece580000
kernel config: https://syzkaller.appspot.com/x/.config?x=2e40c0f41e01837e
dashboard link: https://syzkaller.appspot.com/bug?extid=fa313293506d573be849
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/c6cf04921539/disk-26fd6bff.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/516630c07cc0/vmlinux-26fd6bff.xz
kernel image: https://storage.googleapis.com/syzbot-assets/c1934011cc02/bzImage-26fd6bff.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+fa3132...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in generic_fillattr / inode_update_time

write to 0xffff88810186d10c of 4 bytes by task 14596 on cpu 0:
inode_set_mtime_to_ts include/linux/fs.h:1660 [inline]
inode_update_cmtime fs/inode.c:2133 [inline]
inode_update_time+0x2cc/0x360 fs/inode.c:2158
generic_update_time fs/inode.c:2189 [inline]
file_update_time_flags+0x277/0x2e0 fs/inode.c:2422
file_update_time+0x17/0x20 fs/inode.c:2443
blkdev_write_iter+0x32e/0x4b0 block/fops.c:785
iter_file_splice_write+0x6c4/0xa80 fs/splice.c:736
do_splice_from fs/splice.c:936 [inline]
direct_splice_actor+0x156/0x2a0 fs/splice.c:1159
splice_direct_to_actor+0x311/0x670 fs/splice.c:1103
do_splice_direct_actor fs/splice.c:1202 [inline]
do_splice_direct+0x119/0x1a0 fs/splice.c:1228
do_sendfile+0x382/0x650 fs/read_write.c:1372
__do_sys_sendfile64 fs/read_write.c:1433 [inline]
__se_sys_sendfile64 fs/read_write.c:1419 [inline]
__x64_sys_sendfile64+0x105/0x150 fs/read_write.c:1419
x64_sys_call+0x2dc4/0x3020 arch/x86/include/generated/asm/syscalls_64.h:41
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x12c/0x3b0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88810186d10c of 4 bytes by task 5764 on cpu 1:
inode_get_mtime_nsec include/linux/fs.h:1646 [inline]
inode_get_mtime include/linux/fs.h:1652 [inline]
generic_fillattr+0x20e/0x340 fs/stat.c:102
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+0x118/0x170 fs/stat.c:373
__do_sys_newfstatat fs/stat.c:538 [inline]
__se_sys_newfstatat+0x55/0x3e0 fs/stat.c:532
__x64_sys_newfstatat+0x55/0x70 fs/stat.c:532
x64_sys_call+0x2c64/0x3020 arch/x86/include/generated/asm/syscalls_64.h:263
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x12c/0x3b0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x07730b21 -> 0x080089a2

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 5764 Comm: udevd Tainted: G W syzkaller #0 PREEMPT(full)
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
==================================================================


---
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