Tail of a page straddling inode size must be zeroed when being written
out due to POSIX requirement that modifications of mmaped page beyond
inode size must not be written to the file. ext4_bio_write_page() did
this only for blocks fully beyond inode size but didn't properly zero
blocks partially beyond inode size. Fix this.
The problem has been uncovered by mmap_11-4 test in openposix test suite
(part of LTP).
Reported-by: Xiaoguang Wang <email@example.com>
Signed-off-by: Jan Kara <firstname.lastname@example.org>
Signed-off-by: Theodore Ts'o <email@example.com>