[moderation] [iomap?] KCSAN: data-race in copy_folio_from_iter_atomic / read_lba

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 27fa82620cba Merge tag 'ata-7.1-rc5' of git://git.kernel.o..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=126f8c2e580000
kernel config: https://syzkaller.appspot.com/x/.config?x=2e40c0f41e01837e
dashboard link: https://syzkaller.appspot.com/bug?extid=11a18dbcba72016c164c
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
CC: [bra...@kernel.org djw...@kernel.org linux-...@vger.kernel.org linux-...@vger.kernel.org linu...@vger.kernel.org]

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/dc491bcf1a7c/disk-27fa8262.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/f80d7d0085b0/vmlinux-27fa8262.xz
kernel image: https://storage.googleapis.com/syzbot-assets/009aaf28469f/bzImage-27fa8262.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+11a18d...@syzkaller.appspotmail.com

set_capacity_and_notify: 6 callbacks suppressed
loop7: detected capacity change from 0 to 7
==================================================================
BUG: KCSAN: data-race in copy_folio_from_iter_atomic / read_lba

write to 0xffff88811d9c4000 of 14 bytes by task 3930 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+0x743/0x10b0 lib/iov_iter.c:491
iomap_write_iter fs/iomap/buffered-io.c:1158 [inline]
iomap_file_buffered_write+0x421/0x8f0 fs/iomap/buffered-io.c:1225
blkdev_buffered_write block/fops.c:735 [inline]
blkdev_write_iter+0x3ae/0x4b0 block/fops.c:801
iter_file_splice_write+0x6c4/0xa80 fs/splice.c:736
do_splice_from fs/splice.c:936 [inline]
direct_splice_actor+0x156/0x2a0 fs/splice.c:1159
splice_direct_to_actor+0x311/0x670 fs/splice.c:1103
do_splice_direct_actor fs/splice.c:1202 [inline]
do_splice_direct+0x119/0x1a0 fs/splice.c:1228
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+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+0x12c/0x3b0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88811d9c4000 of 512 bytes by task 3928 on cpu 0:
read_lba+0x132/0x1e0 block/partitions/efi.c:252
find_valid_gpt block/partitions/efi.c:602 [inline]
efi_partition+0x1df/0x1150 block/partitions/efi.c:719
check_partition block/partitions/core.c:143 [inline]
blk_add_partitions block/partitions/core.c:591 [inline]
bdev_disk_changed+0x527/0xe00 block/partitions/core.c:695
loop_reread_partitions+0x48/0xb0 drivers/block/loop.c:447
loop_configure+0x982/0x9c0 drivers/block/loop.c:1096
lo_ioctl+0x5aa/0x13a0 drivers/block/loop.c:1542
blkdev_ioctl+0x387/0x460 block/ioctl.c:797
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:597 [inline]
__se_sys_ioctl+0xce/0x140 fs/ioctl.c:583
__x64_sys_ioctl+0x43/0x50 fs/ioctl.c:583
x64_sys_call+0x1563/0x3020 arch/x86/include/generated/asm/syscalls_64.h:17
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x12c/0x3b0 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: 3928 Comm: syz.1.183 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
==================================================================


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