[38/45] ext4: handle EOF correctly in ext4_bio_write_page()

[Greg KH]

3.0-stable review patch.  If anyone has any objections, please let me know.

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

From: Yongqiang Yang <xiaoqiangnk@xxxxxxxxx>

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@xxxxxxxxx>
Signed-off-by: "Theodore Ts'o" <tytso@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

---
 fs/ext4/page-io.c |   12 ++++++++++++
 1 file changed, 12 insertions(+)

--- a/fs/ext4/page-io.c
+++ b/fs/ext4/page-io.c
@@ -405,6 +405,18 @@ 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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