[moderation] [mm?] KCSAN: data-race in _copy_to_iter / copy_folio_from_iter_atomic

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: aef17cb3d3c4 Revert "mm/damon/Kconfig: enable CONFIG_DAMON..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15b2460c580000
kernel config: https://syzkaller.appspot.com/x/.config?x=f437300db311c188
dashboard link: https://syzkaller.appspot.com/bug?extid=38037e1871d34f9316b4
compiler: Debian clang version 20.1.6 (++20250514063057+1e4d39e07757-1~exp1~20250514183223.118), Debian LLD 20.1.6
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/3b021b9f4a41/disk-aef17cb3.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/ff546f3d73c4/vmlinux-aef17cb3.xz
kernel image: https://storage.googleapis.com/syzbot-assets/07044c10f149/bzImage-aef17cb3.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+38037e...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in _copy_to_iter / copy_folio_from_iter_atomic

write to 0xffff8881425d1000 of 4096 bytes by task 17853 on cpu 1:
memcpy_from_iter lib/iov_iter.c:73 [inline]
iterate_bvec include/linux/iov_iter.h:123 [inline]
iterate_and_advance2 include/linux/iov_iter.h:304 [inline]
iterate_and_advance include/linux/iov_iter.h:328 [inline]
__copy_from_iter lib/iov_iter.c:249 [inline]
copy_folio_from_iter_atomic+0x7fc/0x1170 lib/iov_iter.c:479
generic_perform_write+0x2c2/0x490 mm/filemap.c:4130
shmem_file_write_iter+0xc5/0xf0 mm/shmem.c:3463
iter_file_splice_write+0x5f2/0x970 fs/splice.c:738
do_splice_from fs/splice.c:935 [inline]
direct_splice_actor+0x156/0x2a0 fs/splice.c:1158
splice_direct_to_actor+0x312/0x680 fs/splice.c:1102
do_splice_direct_actor fs/splice.c:1201 [inline]
do_splice_direct+0xda/0x150 fs/splice.c:1227
do_sendfile+0x380/0x650 fs/read_write.c:1370
__do_sys_sendfile64 fs/read_write.c:1431 [inline]
__se_sys_sendfile64 fs/read_write.c:1417 [inline]
__x64_sys_sendfile64+0x105/0x150 fs/read_write.c:1417
x64_sys_call+0xb39/0x2fb0 arch/x86/include/generated/asm/syscalls_64.h:41
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 0xffff8881425d1000 of 4096 bytes by task 17860 on cpu 0:
memcpy_to_iter lib/iov_iter.c:65 [inline]
iterate_bvec include/linux/iov_iter.h:123 [inline]
iterate_and_advance2 include/linux/iov_iter.h:304 [inline]
iterate_and_advance include/linux/iov_iter.h:328 [inline]
_copy_to_iter+0x5fc/0xe30 lib/iov_iter.c:185
copy_page_to_iter+0x18f/0x2d0 lib/iov_iter.c:362
copy_folio_to_iter include/linux/uio.h:204 [inline]
shmem_file_read_iter+0x2d6/0x540 mm/shmem.c:3411
copy_splice_read+0x3c1/0x5f0 fs/splice.c:363
do_splice_read fs/splice.c:978 [inline]
splice_direct_to_actor+0x290/0x680 fs/splice.c:1083
do_splice_direct_actor fs/splice.c:1201 [inline]
do_splice_direct+0xda/0x150 fs/splice.c:1227
do_sendfile+0x380/0x650 fs/read_write.c:1370
__do_sys_sendfile64 fs/read_write.c:1431 [inline]
__se_sys_sendfile64 fs/read_write.c:1417 [inline]
__x64_sys_sendfile64+0x105/0x150 fs/read_write.c:1417
x64_sys_call+0xb39/0x2fb0 arch/x86/include/generated/asm/syscalls_64.h:41
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

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 17860 Comm: syz.2.5678 Tainted: G W 6.16.0-rc1-syzkaller-00004-gaef17cb3d3c4 #0 PREEMPT(voluntary)
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
==================================================================


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[syzbot]

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