stable inclusion
from linux-4.19.179
commit 6ceea9a764b422e32d9028e35d37ad68761ffd2c

--------------------------------

commit caf6912f upstream.

We're not factoring in the start of the file for where to write and
read the swapfile, which leads to very unfortunate side effects of
writing where we should not be...

[This issue only affects swapfiles on filesystems on top of blockdevs
that implement rw_page ops (brd, zram, btt, pmem), and not on top of any
other block devices, in contrast to the upstream commit fix.]

Fixes: dd6bd0d9 ("swap: use bdev_read_page() / bdev_write_page()")
Signed-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NAnthony Iliopoulos <ailiop@suse.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>
Signed-off-by: NCheng Jian <cj.chengjian@huawei.com>