[moderation] [fs?] KCSAN: data-race in file_update_time / inode_update_timestamps (6)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: ac3fd01e4c1e Linux 6.18-rc7
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=156bc612580000
kernel config: https://syzkaller.appspot.com/x/.config?x=655255e3ef31c19b
dashboard link: https://syzkaller.appspot.com/bug?extid=045cf701a1db0ee919d9
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/0b87e3335067/disk-ac3fd01e.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/5d86405bc71d/vmlinux-ac3fd01e.xz
kernel image: https://storage.googleapis.com/syzbot-assets/5cdf269de51b/bzImage-ac3fd01e.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+045cf7...@syzkaller.appspotmail.com

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

read to 0xffff8881004bb884 of 4 bytes by task 4408 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:2336 [inline]
file_update_time+0x87/0x2b0 fs/inode.c:2383
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+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
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:185
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:1416 [inline]
__se_sys_getrandom drivers/char/random.c:1390 [inline]
__x64_sys_getrandom+0xcf/0x1a0 drivers/char/random.c:1390
x64_sys_call+0x1fa6/0x3000 arch/x86/include/generated/asm/syscalls_64.h:319
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

write to 0xffff8881004bb884 of 4 bytes by task 4407 on cpu 1:
inode_set_mtime_to_ts include/linux/fs.h:1839 [inline]
inode_update_timestamps+0x147/0x270 fs/inode.c:2075
generic_update_time fs/inode.c:2110 [inline]
inode_update_time fs/inode.c:2130 [inline]
__file_update_time fs/inode.c:2357 [inline]
file_update_time+0x20e/0x2b0 fs/inode.c:2387
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+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
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:185
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:1416 [inline]
__se_sys_getrandom drivers/char/random.c:1390 [inline]
__x64_sys_getrandom+0xcf/0x1a0 drivers/char/random.c:1390
x64_sys_call+0x1fa6/0x3000 arch/x86/include/generated/asm/syscalls_64.h:319
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

value changed: 0x00a8e54a -> 0x00f93930

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 4407 Comm: syz.3.304 Not tainted syzkaller #0 PREEMPT(voluntary)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
==================================================================


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