[moderation] [mm?] KCSAN: data-race in file_update_time / shmem_fallocate

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: e927c520e1ba Merge tag 'loongarch-fixes-6.18-1' of git://g..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=143f1c12580000
kernel config: https://syzkaller.appspot.com/x/.config?x=d2e0bc0ae94545f7
dashboard link: https://syzkaller.appspot.com/bug?extid=84efd510b34f65b6c7bb
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
CC: [ak...@linux-foundation.org baoli...@linux.alibaba.com hu...@google.com linux-...@vger.kernel.org linu...@kvack.org]

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/971519f3b046/disk-e927c520.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/989c293d066d/vmlinux-e927c520.xz
kernel image: https://storage.googleapis.com/syzbot-assets/4c113f37585c/bzImage-e927c520.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+84efd5...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in file_update_time / shmem_fallocate

write to 0xffff88811b37e6bc of 4 bytes by task 8476 on cpu 1:
inode_set_mtime_to_ts include/linux/fs.h:1839 [inline]
shmem_truncate_range mm/shmem.c:1233 [inline]
shmem_fallocate+0x2df/0x840 mm/shmem.c:3687
vfs_fallocate+0x3b6/0x400 fs/open.c:342
madvise_remove mm/madvise.c:1049 [inline]
madvise_vma_behavior+0x1920/0x1cf0 mm/madvise.c:1346
madvise_walk_vmas mm/madvise.c:1669 [inline]
madvise_do_behavior+0x5b7/0x970 mm/madvise.c:1885
do_madvise+0x10e/0x190 mm/madvise.c:1978
__do_sys_madvise mm/madvise.c:1987 [inline]
__se_sys_madvise mm/madvise.c:1985 [inline]
__x64_sys_madvise+0x64/0x80 mm/madvise.c:1985
x64_sys_call+0x1f1a/0x3000 arch/x86/include/generated/asm/syscalls_64.h:29
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 0xffff88811b37e6bc of 4 bytes by task 8444 on cpu 0:
inode_get_mtime_nsec include/linux/fs.h:1825 [inline]
inode_get_mtime include/linux/fs.h:1831 [inline]
inode_needs_update_time fs/inode.c:2324 [inline]
file_update_time+0x87/0x2b0 fs/inode.c:2371
fault_dirty_shared_page+0xd9/0x3c0 mm/memory.c:3531
do_shared_fault mm/memory.c:5808 [inline]
do_fault mm/memory.c:5854 [inline]
do_pte_missing mm/memory.c:4362 [inline]
handle_pte_fault mm/memory.c:6195 [inline]
__handle_mm_fault mm/memory.c:6336 [inline]
handle_mm_fault+0x165d/0x2be0 mm/memory.c:6505
do_user_addr_fault+0x630/0x1080 arch/x86/mm/fault.c:1336
handle_page_fault arch/x86/mm/fault.c:1476 [inline]
exc_page_fault+0x62/0xa0 arch/x86/mm/fault.c:1532
asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:618

value changed: 0x01c6d633 -> 0x04c1c6b4

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 8444 Comm: syz.0.1809 Tainted: G W syzkaller #0 PREEMPT(voluntary)
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
==================================================================


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