Patch "ext4: correctly migrate a file with a hole at the beginning" has been added to the 4.1-stable tree

This is a note to let you know that I've just added the patch titled

ext4: correctly migrate a file with a hole at the beginning

to the 4.1-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
ext4-correctly-migrate-a-file-with-a-hole-at-the-beginning.patch
and it can be found in the queue-4.1 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Eryu Guan <[email protected]>
Date: Sat, 4 Jul 2015 00:03:44 -0400
Subject: ext4: correctly migrate a file with a hole at the beginning

From: Eryu Guan <[email protected]>

commit 8974fec7d72e3e02752fe0f27b4c3719c78d9a15 upstream.

Currently ext4_ind_migrate() doesn't correctly handle a file which contains a hole at the beginning of the file. This caused the migration to be done incorrectly, and then if there is a subsequent following delayed allocation write to the "hole", this would reclaim the same data blocks again and results in fs corruption.

  # assmuing 4k block size ext4, with delalloc enabled
  # skip the first block and write to the second block
  xfs_io -fc "pwrite 4k 4k" -c "fsync" /mnt/ext4/testfile

  # converting to indirect-mapped file, which would move the data blocks
  # to the beginning of the file, but extent status cache still marks
  # that region as a hole
  chattr -e /mnt/ext4/testfile

  # delayed allocation writes to the "hole", reclaim the same data block
  # again, results in i_blocks corruption
  xfs_io -c "pwrite 0 4k" /mnt/ext4/testfile
  umount /mnt/ext4
  e2fsck -nf /dev/sda6
  ...
  Inode 53, i_blocks is 16, should be 8.  Fix? no
  ...

---
 fs/ext4/migrate.c |    9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

@@ -620,7 +620,7 @@ int ext4_ind_migrate(struct inode *inode
 	struct ext4_inode_info		*ei = EXT4_I(inode);
 	struct ext4_extent		*ex;
 	unsigned int			i, len;
-	ext4_lblk_t			end;
+	ext4_lblk_t			start, end;
 	ext4_fsblk_t			blk;
 	handle_t			*handle;
 	int				ret;

@@ -659,11 +659,12 @@ int ext4_ind_migrate(struct inode *inode
 		goto errout;
 	}
 	if (eh->eh_entries == 0)
-		blk = len = 0;
+		blk = len = start = end = 0;
 	else {
 		len = le16_to_cpu(ex->ee_len);
 		blk = ext4_ext_pblock(ex);
-		end = le32_to_cpu(ex->ee_block) + len - 1;
+		start = le32_to_cpu(ex->ee_block);
+		end = start + len - 1;
 		if (end >= EXT4_NDIR_BLOCKS) {
 			ret = -EOPNOTSUPP;
 			goto errout;

@@ -672,7 +673,7 @@ int ext4_ind_migrate(struct inode *inode
 
 	ext4_clear_inode_flag(inode, EXT4_INODE_EXTENTS);
 	memset(ei->i_data, 0, sizeof(ei->i_data));
-	for (i=0; i < len; i++)
+	for (i = start; i <= end; i++)
 		ei->i_data[i] = cpu_to_le32(blk++);
 	ext4_mark_inode_dirty(handle, inode);
 errout:

Patches currently in stable-queue which might be from [email protected] are

queue-4.1/ext4-correctly-migrate-a-file-with-a-hole-at-the-beginning.patch queue-4.1/ext4-be-more-strict-when-migrating-to-non-extent-based-file.patch