[moderation] [mm?] KCSAN: data-race in _copy_to_iter / copy_folio_from_iter_atomic (4)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 83f1454877cc Merge tag 'ext4_for_linus-7.2-rc1' of git://g..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=10da5b7a580000
kernel config: https://syzkaller.appspot.com/x/.config?x=9731814544890b48
dashboard link: https://syzkaller.appspot.com/bug?extid=c1f41ee8f2d54c6194eb
compiler: Debian clang version 22.1.6 (++20260514074242+fc4aad7b5db3-1~exp1~20260514074407.73), Debian LLD 22.1.6
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/67b1343e22a2/disk-83f14548.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/bd69a260ba4c/vmlinux-83f14548.xz
kernel image: https://storage.googleapis.com/syzbot-assets/681bb79dfb48/bzImage-83f14548.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+c1f41e...@syzkaller.appspotmail.com

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

write to 0xffff88813366d210 of 195 bytes by task 1308 on cpu 1:
memcpy_from_iter lib/iov_iter.c:85 [inline]
iterate_bvec include/linux/iov_iter.h:123 [inline]
iterate_and_advance2 include/linux/iov_iter.h:306 [inline]
iterate_and_advance include/linux/iov_iter.h:330 [inline]
__copy_from_iter lib/iov_iter.c:261 [inline]
copy_folio_from_iter_atomic+0x728/0x10a0 lib/iov_iter.c:491
generic_perform_write+0x2c4/0x490 mm/filemap.c:4354
shmem_file_write_iter+0xc5/0xf0 mm/shmem.c:3477
iter_file_splice_write+0x6a0/0xa60 fs/splice.c:736
do_splice_from fs/splice.c:936 [inline]
direct_splice_actor+0x156/0x280 fs/splice.c:1159
splice_direct_to_actor+0x2f9/0x680 fs/splice.c:1103
do_splice_direct_actor fs/splice.c:1202 [inline]
do_splice_direct+0x119/0x1a0 fs/splice.c:1228
do_sendfile+0x37d/0x640 fs/read_write.c:1371
__do_sys_sendfile64 fs/read_write.c:1432 [inline]
__se_sys_sendfile64 fs/read_write.c:1418 [inline]
__x64_sys_sendfile64+0x105/0x150 fs/read_write.c:1418
x64_sys_call+0x2dc4/0x3020 arch/x86/include/generated/asm/syscalls_64.h:41
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x136/0x3c0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88813366d251 of 65 bytes by task 1310 on cpu 0:
memcpy_to_iter lib/iov_iter.c:77 [inline]
iterate_bvec include/linux/iov_iter.h:123 [inline]
iterate_and_advance2 include/linux/iov_iter.h:306 [inline]
iterate_and_advance include/linux/iov_iter.h:330 [inline]
_copy_to_iter+0x605/0xea0 lib/iov_iter.c:197
copy_page_to_iter+0x174/0x210 lib/iov_iter.c:374
copy_folio_to_iter include/linux/uio.h:204 [inline]
shmem_file_read_iter+0x29c/0x4b0 mm/shmem.c:3425
copy_splice_read+0x47a/0x6b0 fs/splice.c:362
do_splice_read fs/splice.c:979 [inline]
splice_direct_to_actor+0x27c/0x680 fs/splice.c:1084
do_splice_direct_actor fs/splice.c:1202 [inline]
do_splice_direct+0x119/0x1a0 fs/splice.c:1228
do_sendfile+0x37d/0x640 fs/read_write.c:1371
__do_sys_sendfile64 fs/read_write.c:1432 [inline]
__se_sys_sendfile64 fs/read_write.c:1418 [inline]
__x64_sys_sendfile64+0x105/0x150 fs/read_write.c:1418
x64_sys_call+0x2dc4/0x3020 arch/x86/include/generated/asm/syscalls_64.h:41
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x136/0x3c0 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: 1310 Comm: syz.1.7455 Tainted: G W syzkaller #0 PREEMPT(lazy)
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
==================================================================


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