ext4: race-condition protection for ext4_convert_unwritten_extents_endio

We assumed that at the time we call ext4_convert_unwritten_extents_endio()
extent in question is fully inside [map.m_lblk, map->m_len] because
it was already split during submission.  But this may not be true due to
a race between writeback vs fallocate.

If extent in question is larger than requested we will split it again.
Special precautions should being done if zeroout required because
[map.m_lblk, map->m_len] already contains valid data.

Signed-off-by: Dmitry Monakhov <dmonakhov@openvz.org>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Cc: stable@vger.kernel.org
static unsigned int ext4_ext_check_overlap(struct ext4_sb_info *sbi,
					   struct inode *inode,
					   struct ext4_extent *newext,
					   struct ext4_ext_path *path)
{
	ext4_lblk_t b1, b2;
	unsigned int depth, len1;
	unsigned int ret = 0;

	b1 = le32_to_cpu(newext->ee_block);
	len1 = ext4_ext_get_actual_len(newext);
	depth = ext_depth(inode);
	if (!path[depth].p_ext)
		goto out;
	b2 = le32_to_cpu(path[depth].p_ext->ee_block);
	b2 &= ~(sbi->s_cluster_ratio - 1);

	/*
	 * get the next allocated block if the extent in the path
	 * is before the requested block(s)
	 */
	if (b2 < b1) {
		b2 = ext4_ext_next_allocated_block(path);
		if (b2 == EXT_MAX_BLOCKS)
			goto out;
		b2 &= ~(sbi->s_cluster_ratio - 1);
	}

	/* check for wrap through zero on extent logical start block*/
	if (b1 + len1 < b1) {
		len1 = EXT_MAX_BLOCKS - b1;
		newext->ee_len = cpu_to_le16(len1);
		ret = 1;
	}

	/* check for overlap */
	if (b1 + len1 > b2) {
		newext->ee_len = cpu_to_le16(b2 - b1);
		ret = 1;
	}
out:
	return ret;
}

static unsigned int ext4_ext_check_overlap(struct ext4_sb_info *sbi,
					   struct inode *inode,
					   struct ext4_extent *newext,
					   struct ext4_ext_path *path)
{
	ext4_lblk_t b1, b2;
	unsigned int depth, len1;
	unsigned int ret = 0;

	b1 = le32_to_cpu(newext->ee_block);
	len1 = ext4_ext_get_actual_len(newext);
	depth = ext_depth(inode);
	if (!path[depth].p_ext)
		goto out;
	b2 = le32_to_cpu(path[depth].p_ext->ee_block);
	b2 &= ~(sbi->s_cluster_ratio - 1);

	/*
	 * get the next allocated block if the extent in the path
	 * is before the requested block(s)
	 */
	if (b2 < b1) {
		b2 = ext4_ext_next_allocated_block(path);
		if (b2 == EXT_MAX_BLOCKS)
			goto out;
		b2 &= ~(sbi->s_cluster_ratio - 1);
	}

	/* check for wrap through zero on extent logical start block*/
	if (b1 + len1 < b1) {
		len1 = EXT_MAX_BLOCKS - b1;
		newext->ee_len = cpu_to_le16(len1);
		ret = 1;
	}

	/* check for overlap */
	if (b1 + len1 > b2) {
		newext->ee_len = cpu_to_le16(b2 - b1);
		ret = 1;
	}
out:
	return ret;
}
