[PATCH v2 13/16] btrfs: remove the free space inode special cases from the COW paths

@@ -1366,11 +1366,6 @@ static noinline int cow_file_range(struct btrfs_inode *inode,
 		goto out_unlock;
 	}
 
-	if (btrfs_is_free_space_inode(inode)) {
-		ret = -EINVAL;
-		goto out_unlock;
-	}
-
 	num_bytes = ALIGN(end - start + 1, blocksize);
 	num_bytes = max(blocksize,  num_bytes);
 	ASSERT(num_bytes <= btrfs_super_total_bytes(fs_info->super_copy));

@@ -1680,7 +1675,6 @@ static int fallback_to_cow(struct btrfs_inode *inode,
 			   struct folio *locked_folio, const u64 start,
 			   const u64 end)
 {
-	const bool is_space_ino = btrfs_is_free_space_inode(inode);
 	const bool is_reloc_ino = btrfs_is_data_reloc_root(inode->root);
 	const u64 range_bytes = end + 1 - start;
 	struct extent_io_tree *io_tree = &inode->io_tree;

@@ -1713,23 +1707,22 @@ static int fallback_to_cow(struct btrfs_inode *inode,
 	 *    extent_clear_unlock_delalloc()) the bytes_may_use counter of the
 	 *    data space info, which we incremented in the step above.
 	 *
-	 * If we need to fallback to cow and the inode corresponds to a free
-	 * space cache inode or an inode of the data relocation tree, we must
-	 * also increment bytes_may_use of the data space_info for the same
-	 * reason. Space caches and relocated data extents always get a prealloc
-	 * extent for them, however scrub or balance may have set the block
-	 * group that contains that extent to RO mode and therefore force COW
-	 * when starting writeback.
+	 * If we need to fallback to cow and the inode is in the data relocation
+	 * tree, we must also increment bytes_may_use of the data space_info for
+	 * the same reason. Relocated data extents always get a prealloc extent,
+	 * however scrub or balance may have set the block group that contains
+	 * that extent to RO mode and therefore force COW when starting
+	 * writeback.
 	 */
 	btrfs_lock_extent(io_tree, start, end, &cached_state);
 	count = btrfs_count_range_bits(io_tree, &range_start, end, range_bytes,
 				       EXTENT_NORESERVE, false, NULL);
-	if (count > 0 || is_space_ino || is_reloc_ino) {
+	if (count > 0 || is_reloc_ino) {
 		u64 bytes = count;
 		struct btrfs_fs_info *fs_info = inode->root->fs_info;
 		struct btrfs_space_info *sinfo = fs_info->data_sinfo;
 
-		if (is_space_ino || is_reloc_ino)
+		if (is_reloc_ino)
 			bytes = range_bytes;
 
 		spin_lock(&sinfo->lock);

@@ -1794,7 +1787,6 @@ static int can_nocow_file_extent(struct btrfs_path *path,
 				 struct btrfs_inode *inode,
 				 struct can_nocow_file_extent_args *args)
 {
-	const bool is_freespace_inode = btrfs_is_free_space_inode(inode);
 	struct extent_buffer *leaf = path->nodes[0];
 	struct btrfs_root *root = inode->root;
 	struct btrfs_file_extent_item *fi;

@@ -1807,8 +1799,7 @@ static int can_nocow_file_extent(struct btrfs_path *path,
 	bool nowait = path->nowait;
 
 	/* If there are pending snapshots for this root, we must do COW. */
-	if (args->writeback_path && !is_freespace_inode &&
-	    atomic_read(&root->snapshot_force_cow))
+	if (args->writeback_path && atomic_read(&root->snapshot_force_cow))
 		goto out;
 
 	fi = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_file_extent_item);

@@ -1857,7 +1848,6 @@ static int can_nocow_file_extent(struct btrfs_path *path,
 
 	ret = btrfs_cross_ref_exist(inode, key->offset - args->file_extent.offset,
 				    args->file_extent.disk_bytenr, path);
-	WARN_ON_ONCE(ret > 0 && is_freespace_inode);
 	if (ret != 0)
 		goto out;
 

@@ -1892,7 +1882,6 @@ static int can_nocow_file_extent(struct btrfs_path *path,
 	ret = btrfs_lookup_csums_list(csum_root, io_start,
 				      io_start + args->file_extent.num_bytes - 1,
 				      NULL, nowait);
-	WARN_ON_ONCE(ret > 0 && is_freespace_inode);
 	if (ret != 0)
 		goto out;
 

@@ -3203,6 +3192,7 @@ int btrfs_finish_one_ordered(struct btrfs_ordered_extent *ordered_extent)
 	int compress_type = 0;
 	int ret = 0;
 	u64 logical_len = ordered_extent->num_bytes;
+	u64 unwritten_start;
 	bool truncated = false;
 	bool clear_reserved_extent = true;
 	unsigned int clear_bits = 0;

@@ -3364,29 +3354,11 @@ int btrfs_finish_one_ordered(struct btrfs_ordered_extent *ordered_extent)
 		if (ret)
 			btrfs_mark_ordered_extent_error(ordered_extent);
 
-		/*
-		 * Drop extent maps for the part of the extent we didn't write.
-		 *
-		 * We have an exception here for the free_space_inode, this is
-		 * because when we do btrfs_get_extent() on the free space inode
-		 * we will search the commit root.  If this is a new block group
-		 * we won't find anything, and we will trip over the assert in
-		 * writepage where we do ASSERT(em->block_start !=
-		 * EXTENT_MAP_HOLE).
-		 *
-		 * Theoretically we could also skip this for any NOCOW extent as
-		 * we don't mess with the extent map tree in the NOCOW case, but
-		 * for now simply skip this if we are the free space inode.
-		 */
-		if (!btrfs_is_free_space_inode(inode)) {
-			u64 unwritten_start = start;
-
-			if (truncated)
-				unwritten_start += logical_len;
-
-			btrfs_drop_extent_map_range(inode, unwritten_start,
-						    end, false);
-		}
+		/* Drop extent maps for the part of the extent we didn't write. */
+		unwritten_start = start;
+		if (truncated)
+			unwritten_start += logical_len;
+		btrfs_drop_extent_map_range(inode, unwritten_start, end, false);
 
 		/*
 		 * If the ordered extent had an IOERR or something else went