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

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 8a5203c630c6 Merge tag 'v7.0-rc-part1-smb3-client-fixes' o..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=132e3402580000
kernel config: https://syzkaller.appspot.com/x/.config?x=8e27f4588a0f2183
dashboard link: https://syzkaller.appspot.com/bug?extid=a5767cf77f098bb99cef
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/c547458268e2/disk-8a5203c6.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/e275bd321af4/vmlinux-8a5203c6.xz
kernel image: https://storage.googleapis.com/syzbot-assets/d756c6f6b4dd/bzImage-8a5203c6.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+a5767c...@syzkaller.appspotmail.com

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

write to 0xffff888119a12c8c of 4 bytes by task 17708 on cpu 1:
inode_set_mtime_to_ts include/linux/fs.h:1659 [inline]
inode_update_cmtime fs/inode.c:2130 [inline]
inode_update_time+0x2cc/0x360 fs/inode.c:2155
generic_update_time fs/inode.c:2186 [inline]
file_update_time_flags+0x277/0x2e0 fs/inode.c:2419
file_update_time+0x17/0x20 fs/inode.c:2440
shmem_file_write_iter+0x9c/0xf0 mm/shmem.c:3516
iter_file_splice_write+0x6bc/0xa80 fs/splice.c:738
do_splice_from fs/splice.c:938 [inline]
direct_splice_actor+0x156/0x2a0 fs/splice.c:1161
splice_direct_to_actor+0x311/0x670 fs/splice.c:1105
do_splice_direct_actor fs/splice.c:1204 [inline]
do_splice_direct+0x119/0x1a0 fs/splice.c:1230
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+0x2db1/0x3000 arch/x86/include/generated/asm/syscalls_64.h:41
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xc0/0x2a0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff888119a12c8c of 4 bytes by task 17712 on cpu 0:
inode_get_mtime_nsec include/linux/fs.h:1645 [inline]
inode_get_mtime include/linux/fs.h:1651 [inline]
relatime_need_update fs/inode.c:2065 [inline]
atime_needs_update+0x2a8/0x3e0 fs/inode.c:2229
touch_atime+0x4a/0x330 fs/inode.c:2244
file_accessed include/linux/fs.h:2263 [inline]
shmem_file_read_iter+0x477/0x540 mm/shmem.c:3499
copy_splice_read+0x471/0x6c0 fs/splice.c:363
do_splice_read fs/splice.c:981 [inline]
splice_direct_to_actor+0x28f/0x670 fs/splice.c:1086
do_splice_direct_actor fs/splice.c:1204 [inline]
do_splice_direct+0x119/0x1a0 fs/splice.c:1230
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+0x2db1/0x3000 arch/x86/include/generated/asm/syscalls_64.h:41
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xc0/0x2a0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x0e4e28d8 -> 0x0f07fcd5

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 17712 Comm: syz.1.4327 Tainted: G W syzkaller #0 PREEMPT(voluntary)
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/24/2026
==================================================================


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