Re: [PATCH 2/3] ext4: fix ZERO_RANGE test failure in data journalling mode

[Theodore Ts'o <tytso@mit.edu>]

So a couple of things.  First of all, ext4_force_commit() is a very
expensive call, so calling it twice is really not a good idea.

Secondly, in the ext4_collapse_range() you are calling
ext4_force_commit() before filemap_write_and_wait_range().

	/* Call ext4_force_commit to flush all data in case of data=journal. */
	if (ext4_should_journal_data(inode)) {
		ret = ext4_force_commit(inode->i_sb);
		if (ret)
			return ret;
	}

	/* Write out all dirty pages */
	ret = filemap_write_and_wait_range(inode->i_mapping, offset, -1);
	if (ret)
		return ret;

Shouldn't we reverse these two calls?

Finally, I'm wondering if we would be better off creating a new
explicit EXT4_I(inode)->i_write_mutex which is used to block new
writes from starting.  This could also be used to subsume the
ext4_aio_mutex.

						- Ted