[moderation] [ext4?] KCSAN: data-race in file_update_time_flags / inode_update_timestamps

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 8f0b4cce4481 Linux 6.19-rc1
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=12b509b4580000
kernel config: https://syzkaller.appspot.com/x/.config?x=b319ff1b6a2797ca
dashboard link: https://syzkaller.appspot.com/bug?extid=1362842535f601e5a890
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
CC: [adilger...@dilger.ca linux...@vger.kernel.org linux-...@vger.kernel.org ty...@mit.edu]

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/0397a0339bfd/disk-8f0b4cce.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/1c266f6e8d6b/vmlinux-8f0b4cce.xz
kernel image: https://storage.googleapis.com/syzbot-assets/a748ab0188b2/bzImage-8f0b4cce.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+136284...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in file_update_time_flags / inode_update_timestamps

write to 0xffff888117d6578c of 4 bytes by task 15029 on cpu 0:
inode_set_mtime_to_ts include/linux/fs.h:1658 [inline]
inode_update_timestamps+0x147/0x270 fs/inode.c:2113
generic_update_time fs/inode.c:2148 [inline]
inode_update_time fs/inode.c:2168 [inline]
file_update_time_flags+0x26c/0x310 fs/inode.c:2395
file_update_time+0x17/0x20 fs/inode.c:2416
ext4_page_mkwrite+0x18c/0xb90 fs/ext4/inode.c:6668
do_page_mkwrite mm/memory.c:3528 [inline]
do_shared_fault mm/memory.c:5831 [inline]
do_fault mm/memory.c:5893 [inline]
do_pte_missing mm/memory.c:4401 [inline]
handle_pte_fault mm/memory.c:6273 [inline]
__handle_mm_fault mm/memory.c:6411 [inline]
handle_mm_fault+0x1601/0x2c60 mm/memory.c:6580
do_user_addr_fault+0x78d/0x1080 arch/x86/mm/fault.c:1387
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
rep_movs_alternative+0x4a/0x90 arch/x86/lib/copy_user_64.S:68
copy_user_generic arch/x86/include/asm/uaccess_64.h:126 [inline]
raw_copy_to_user arch/x86/include/asm/uaccess_64.h:147 [inline]
copy_to_user_iter lib/iov_iter.c:25 [inline]
iterate_ubuf include/linux/iov_iter.h:30 [inline]
iterate_and_advance2 include/linux/iov_iter.h:302 [inline]
iterate_and_advance include/linux/iov_iter.h:330 [inline]
_copy_to_iter+0x141/0xe70 lib/iov_iter.c:197
copy_to_iter include/linux/uio.h:220 [inline]
get_random_bytes_user+0x12d/0x290 drivers/char/random.c:473
__do_sys_getrandom drivers/char/random.c:1420 [inline]
__se_sys_getrandom drivers/char/random.c:1394 [inline]
__x64_sys_getrandom+0xcf/0x1a0 drivers/char/random.c:1394
x64_sys_call+0x1beb/0x3000 arch/x86/include/generated/asm/syscalls_64.h:319
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd8/0x2c0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff888117d6578c of 4 bytes by task 15013 on cpu 1:
inode_get_mtime_nsec include/linux/fs.h:1644 [inline]
inode_get_mtime include/linux/fs.h:1650 [inline]
file_update_time_flags+0xad/0x310 fs/inode.c:2378
file_update_time+0x17/0x20 fs/inode.c:2416
ext4_page_mkwrite+0x18c/0xb90 fs/ext4/inode.c:6668
do_page_mkwrite mm/memory.c:3528 [inline]
do_shared_fault mm/memory.c:5831 [inline]
do_fault mm/memory.c:5893 [inline]
do_pte_missing mm/memory.c:4401 [inline]
handle_pte_fault mm/memory.c:6273 [inline]
__handle_mm_fault mm/memory.c:6411 [inline]
handle_mm_fault+0x1601/0x2c60 mm/memory.c:6580
do_user_addr_fault+0x3fe/0x1080 arch/x86/mm/fault.c:1387
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: 0x1eb6dc18 -> 0x32624298

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 15013 Comm: syz.4.4271 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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