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Subject[45/53] ext4: handle EOF correctly in ext4_bio_write_page()
3.1-stable review patch.  If anyone has any objections, please let me know.

------------------
From: Yongqiang Yang <xiaoqiangnk@gmail.com>

commit 5a0dc7365c240795bf190766eba7a27600be3b3e upstream.

We need to zero out part of a page which beyond EOF before setting uptodate,
otherwise, mapread or write will see non-zero data beyond EOF.

Signed-off-by: Yongqiang Yang <xiaoqiangnk@gmail.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
fs/ext4/page-io.c | 12 ++++++++++++
1 file changed, 12 insertions(+)
--- a/fs/ext4/page-io.c
+++ b/fs/ext4/page-io.c
@@ -401,6 +401,18 @@ int ext4_bio_write_page(struct ext4_io_s

block_end = block_start + blocksize;
if (block_start >= len) {
+ /*
+ * Comments copied from block_write_full_page_endio:
+ *
+ * The page straddles i_size. It must be zeroed out on
+ * each and every writepage invocation because it may
+ * be mmapped. "A file is mapped in multiples of the
+ * page size. For a file that is not a multiple of
+ * the page size, the remaining memory is zeroed when
+ * mapped, and writes to that region are not written
+ * out to the file."
+ */
+ zero_user_segment(page, block_start, block_end);
clear_buffer_dirty(bh);
set_buffer_uptodate(bh);
continue;



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