[moderation] [fs?] KCSAN: data-race in file_modified_flags / inode_update_timestamps (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 850925a8133c Merge tag '9p-for-6.12-rc5' of https://github..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1460be5f980000
kernel config: https://syzkaller.appspot.com/x/.config?x=1ac60661f96136b0
dashboard link: https://syzkaller.appspot.com/bug?extid=aceb9194512bbc9aaba4
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
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/c69e3f89b64a/disk-850925a8.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/52afd4ba1fff/vmlinux-850925a8.xz
kernel image: https://storage.googleapis.com/syzbot-assets/7235f45548e2/bzImage-850925a8.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+aceb91...@syzkaller.appspotmail.com

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

write to 0xffff8881140060ec of 4 bytes by task 17800 on cpu 0:
inode_set_mtime_to_ts include/linux/fs.h:1644 [inline]
inode_update_timestamps+0x166/0x280 fs/inode.c:2001
generic_update_time fs/inode.c:2036 [inline]
inode_update_time fs/inode.c:2056 [inline]
__file_update_time fs/inode.c:2245 [inline]
file_update_time+0x220/0x2b0 fs/inode.c:2275
fault_dirty_shared_page+0xde/0x340 mm/memory.c:3204
do_shared_fault mm/memory.c:5378 [inline]
do_fault mm/memory.c:5424 [inline]
do_pte_missing mm/memory.c:3965 [inline]
handle_pte_fault mm/memory.c:5755 [inline]
__handle_mm_fault mm/memory.c:5898 [inline]
handle_mm_fault+0x1370/0x2a80 mm/memory.c:6066
do_user_addr_fault arch/x86/mm/fault.c:1338 [inline]
handle_page_fault arch/x86/mm/fault.c:1481 [inline]
exc_page_fault+0x3b9/0x650 arch/x86/mm/fault.c:1539
asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:623

read to 0xffff8881140060ec of 4 bytes by task 17802 on cpu 1:
inode_get_mtime_nsec include/linux/fs.h:1630 [inline]
inode_get_mtime include/linux/fs.h:1636 [inline]
inode_needs_update_time fs/inode.c:2224 [inline]
file_modified_flags+0xe0/0x330 fs/inode.c:2310
file_modified+0x17/0x20 fs/inode.c:2332
shmem_fallocate+0x80a/0x860 mm/shmem.c:3529
vfs_fallocate+0x368/0x3b0 fs/open.c:333
ksys_fallocate fs/open.c:356 [inline]
__do_sys_fallocate fs/open.c:364 [inline]
__se_sys_fallocate fs/open.c:362 [inline]
__x64_sys_fallocate+0x79/0xc0 fs/open.c:362
x64_sys_call+0x2783/0x2d60 arch/x86/include/generated/asm/syscalls_64.h:286
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xc9/0x1c0 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x06acdd0a -> 0x0739b3ba

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 17802 Comm: syz.3.3798 Tainted: G W 6.12.0-rc4-syzkaller-00261-g850925a8133c #0
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
==================================================================


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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.