linux-kernel - [45/53] ext4: handle EOF correctly in ext4_bio_write

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Message-Id: <20111216194601.431539642@clark.kroah.org>
Date:	Fri, 16 Dec 2011 11:45:42 -0800
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk, Yongqiang Yang <xiaoqiangnk@...il.com>,
	"Theodore Tso" <tytso@....edu>
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@...il.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@...il.com>
Signed-off-by: "Theodore Ts'o" <tytso@....edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.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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