btrfs: remove non-standard extent handling in __extent_writepage_io

__extent_writepage_io is never called for compressed or inline extents,
or holes.  Remove the not quite working code for them and replace it with
asserts that these cases don't happen.
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/extent_io.c

@@ -1361,7 +1361,6 @@ static noinline_for_stack int __extent_writepage_io(struct btrfs_inode *inode,
 	struct extent_map *em;
 	int ret = 0;
 	int nr = 0;
-	bool compressed;
 
 	ret = btrfs_writepage_cow_fixup(page);
 	if (ret) {
@@ -1419,10 +1418,14 @@ static noinline_for_stack int __extent_writepage_io(struct btrfs_inode *inode,
 		ASSERT(cur < end);
 		ASSERT(IS_ALIGNED(em->start, fs_info->sectorsize));
 		ASSERT(IS_ALIGNED(em->len, fs_info->sectorsize));
+
 		block_start = em->block_start;
-		compressed = test_bit(EXTENT_FLAG_COMPRESSED, &em->flags);
 		disk_bytenr = em->block_start + extent_offset;
 
+		ASSERT(!test_bit(EXTENT_FLAG_COMPRESSED, &em->flags));
+		ASSERT(block_start != EXTENT_MAP_HOLE);
+		ASSERT(block_start != EXTENT_MAP_INLINE);
+
 		/*
 		 * Note that em_end from extent_map_end() and dirty_range_end from
 		 * find_next_dirty_byte() are all exclusive
@@ -1431,22 +1434,6 @@ static noinline_for_stack int __extent_writepage_io(struct btrfs_inode *inode,
 		free_extent_map(em);
 		em = NULL;
 
-		/*
-		 * compressed and inline extents are written through other
-		 * paths in the FS
-		 */
-		if (compressed || block_start == EXTENT_MAP_HOLE ||
-		    block_start == EXTENT_MAP_INLINE) {
-			if (compressed)
-				nr++;
-			else
-				btrfs_writepage_endio_finish_ordered(inode,
-						page, cur, cur + iosize - 1, true);
-			btrfs_page_clear_dirty(fs_info, page, cur, iosize);
-			cur += iosize;
-			continue;
-		}
-
 		btrfs_set_range_writeback(inode, cur, cur + iosize - 1);
 		if (!PageWriteback(page)) {
 			btrfs_err(inode->root->fs_info,