linux-kernel - [PATCH 3.16.y-ckt 123/133] ext4: fix loss of delalloc extent info in ext4_zero

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Message-Id: <1443606681-7124-124-git-send-email-luis.henriques@canonical.com>
Date:	Wed, 30 Sep 2015 10:51:11 +0100
From:	Luis Henriques <luis.henriques@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Eric Whitney <enwlinux@...il.com>, Theodore Ts'o <tytso@....edu>,
	Luis Henriques <luis.henriques@...onical.com>
Subject: [PATCH 3.16.y-ckt 123/133] ext4: fix loss of delalloc extent info in ext4_zero_range()

3.16.7-ckt18 -stable review patch.  If anyone has any objections, please let me know.

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

From: Eric Whitney <enwlinux@...il.com>

commit 94426f4b9648154dc5a6760b59e6953e640ab3b1 upstream.

In ext4_zero_range(), removing a file's entire block range from the
extent status tree removes all records of that file's delalloc extents.
The delalloc accounting code uses this information, and its loss can
then lead to accounting errors and kernel warnings at writeback time and
subsequent file system damage.  This is most noticeable on bigalloc
file systems where code in ext4_ext_map_blocks() handles cases where
delalloc extents share clusters with a newly allocated extent.

Because we're not deleting a block range and are correctly updating the
status of its associated extent, there is no need to remove anything
from the extent status tree.

When this patch is combined with an unrelated bug fix for
ext4_zero_range(), kernel warnings and e2fsck errors reported during
xfstests runs on bigalloc filesystems are greatly reduced without
introducing regressions on other xfstests-bld test scenarios.

Signed-off-by: Eric Whitney <enwlinux@...il.com>
Signed-off-by: Theodore Ts'o <tytso@....edu>
Signed-off-by: Luis Henriques <luis.henriques@...onical.com>
---
 fs/ext4/extents.c | 13 -------------
 1 file changed, 13 deletions(-)

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index ba5d7dc47b3e..e41ec5034bad 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -4846,19 +4846,6 @@ static long ext4_zero_range(struct file *file, loff_t offset,
 					     flags, mode);
 		if (ret)
 			goto out_dio;
-		/*
-		 * Remove entire range from the extent status tree.
-		 *
-		 * ext4_es_remove_extent(inode, lblk, max_blocks) is
-		 * NOT sufficient.  I'm not sure why this is the case,
-		 * but let's be conservative and remove the extent
-		 * status tree for the entire inode.  There should be
-		 * no outstanding delalloc extents thanks to the
-		 * filemap_write_and_wait_range() call above.
-		 */
-		ret = ext4_es_remove_extent(inode, 0, EXT_MAX_BLOCKS);
-		if (ret)
-			goto out_dio;
 	}
 	if (!partial_begin && !partial_end)
 		goto out_dio;
--
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