linux-kernel - [44/53] ext4: avoid potential hang in mpage_submit

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Date:	Fri, 16 Dec 2011 11:45:41 -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: [44/53] ext4: avoid potential hang in mpage_submit_io() when blocksize < pagesize

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

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

From: Yongqiang Yang <xiaoqiangnk@...il.com>

commit 13a79a4741d37fda2fbafb953f0f301dc007928f upstream.

If there is an unwritten but clean buffer in a page and there is a
dirty buffer after the buffer, then mpage_submit_io does not write the
dirty buffer out.  As a result, da_writepages loops forever.

This patch fixes the problem by checking dirty flag.

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/inode.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -1261,8 +1261,11 @@ static int mpage_da_submit_io(struct mpa
 					clear_buffer_unwritten(bh);
 				}
 
-				/* skip page if block allocation undone */
-				if (buffer_delay(bh) || buffer_unwritten(bh))
+				/*
+				 * skip page if block allocation undone and
+				 * block is dirty
+				 */
+				if (ext4_bh_delay_or_unwritten(NULL, bh))
 					skip_page = 1;
 				bh = bh->b_this_page;
 				block_start += bh->b_size;


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