linux-ext4 - [PATCH] ext4: ext4_split_extent shoult take care about extent zeroout v2

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Date:	Thu, 31 Jan 2013 18:48:58 +0400
From:	Dmitry Monakhov <dmonakhov@...nvz.org>
To:	linux-ext4@...r.kernel.org
Cc:	tytso@....edu, jack@...e.cz, xiaoqiangnk@...il.com,
	Dmitry Monakhov <dmonakhov@...nvz.org>
Subject: [PATCH] ext4: ext4_split_extent shoult take care about extent zeroout v2

When ext4_split_extent_at() ends up doing zeroout & conversion to
initialized instead of split & conversion, ext4_split_extent() gets
confused and can wrongly mark the extent back as uninitialized resulting in
end IO code getting confused from large unwritten extents and may result in
data loss.

The example of problematic behavior is:
			    lblk len              lblk len
  ext4_split_extent() (ex=[1000,30,uninit], map=[1010,10])
    ext4_split_extent_at() (split [1000,30,uninit] at 1020)
      ext4_ext_insert_extent() -> ENOSPC
      ext4_ext_zeroout()
	 -> extent [1000,30] is now initialized
    ext4_split_extent_at() (split [1000,30,init] at 1010,
			     MARK_UNINIT1 | MARK_UNINIT2)
      -> extent is split and parts marked as uninitialized

Fix the problem by rechecking extent type after the first
ext4_split_extent_at() returns. None of split_flags can not be applied to
initialized extent so this patch also add BUG_ON to prevent similar issues
in future.

TESTCASE: https://github.com/dmonakhov/xfstests/commit/1a1c4f337d4d198803436c63a56625b1a78d8a5e

Signed-off-by: Dmitry Monakhov <dmonakhov@...nvz.org>
---
 fs/ext4/extents.c |   22 ++++++++++++++++------
 1 files changed, 16 insertions(+), 6 deletions(-)

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index fd51469..05222d5 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -2982,6 +2982,10 @@ static int ext4_split_extent_at(handle_t *handle,
 	newblock = split - ee_block + ext4_ext_pblock(ex);
 
 	BUG_ON(split < ee_block || split >= (ee_block + ee_len));
+	BUG_ON(!ext4_ext_is_uninitialized(ex) &&
+	       split_flag & (EXT4_EXT_MAY_ZEROOUT |
+			     EXT4_EXT_MARK_UNINIT1 |
+			     EXT4_EXT_MARK_UNINIT2));
 
 	err = ext4_ext_get_access(handle, inode, path + depth);
 	if (err)
@@ -3091,18 +3095,24 @@ static int ext4_split_extent(handle_t *handle,
 		if (err)
 			goto out;
 	}
-
+	/*
+	 * Update path is required because previous ext4_split_extent_at() may
+	 * result in split of original leaf or extent zeroout.
+	 */
 	ext4_ext_drop_refs(path);
 	path = ext4_ext_find_extent(inode, map->m_lblk, path);
 	if (IS_ERR(path))
 		return PTR_ERR(path);
+	depth = ext_depth(inode);
+	ex = path[depth].p_ext;
+	uninitialized = ext4_ext_is_uninitialized(ex);
+	split_flag1 = 0;
 
 	if (map->m_lblk >= ee_block) {
-		split_flag1 = split_flag & EXT4_EXT_MAY_ZEROOUT;
-		if (uninitialized)
-			split_flag1 |= EXT4_EXT_MARK_UNINIT1;
-		if (split_flag & EXT4_EXT_MARK_UNINIT2)
-			split_flag1 |= EXT4_EXT_MARK_UNINIT2;
+		if (uninitialized) {
+			split_flag1 = EXT4_EXT_MARK_UNINIT1;
+			split_flag1 |= split_flag & (EXT4_EXT_MAY_ZEROOUT | EXT4_EXT_MARK_UNINIT2);
+		}
 		err = ext4_split_extent_at(handle, inode, path,
 				map->m_lblk, split_flag1, flags);
 		if (err)
-- 
1.7.1

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