btrfs: remove BUG_ON()'s in add_new_free_space()

At add_new_free_space() we have these BUG_ON()'s that are there to deal
with any failure to add free space to the in memory free space cache.
Such failures are mostly -ENOMEM that should be very rare. However there's
no need to have these BUG_ON()'s, we can just return any error to the
caller and all callers and their upper call chain are already dealing with
errors.

So just make add_new_free_space() return any errors, while removing the
BUG_ON()'s, and returning the total amount of added free space to an
optional u64 pointer argument.

Reported-by: syzbot+3ba856e07b7127889d8c@syzkaller.appspotmail.com
Link: https://lore.kernel.org/linux-btrfs/000000000000e9cb8305ff4e8327@google.com/
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/block-group.c

@@ -499,12 +499,16 @@ static void fragment_free_space(struct btrfs_block_group *block_group)
  * used yet since their free space will be released as soon as the transaction
  * commits.
  */
-u64 add_new_free_space(struct btrfs_block_group *block_group, u64 start, u64 end)
+int add_new_free_space(struct btrfs_block_group *block_group, u64 start, u64 end,
+		       u64 *total_added_ret)
 {
 	struct btrfs_fs_info *info = block_group->fs_info;
-	u64 extent_start, extent_end, size, total_added = 0;
+	u64 extent_start, extent_end, size;
 	int ret;
 
+	if (total_added_ret)
+		*total_added_ret = 0;
+
 	while (start < end) {
 		ret = find_first_extent_bit(&info->excluded_extents, start,
 					    &extent_start, &extent_end,
@@ -517,10 +521,12 @@ u64 add_new_free_space(struct btrfs_block_group *block_group, u64 start, u64 end
 			start = extent_end + 1;
 		} else if (extent_start > start && extent_start < end) {
 			size = extent_start - start;
-			total_added += size;
 			ret = btrfs_add_free_space_async_trimmed(block_group,
 								 start, size);
-			BUG_ON(ret); /* -ENOMEM or logic error */
+			if (ret)
+				return ret;
+			if (total_added_ret)
+				*total_added_ret += size;
 			start = extent_end + 1;
 		} else {
 			break;
@@ -529,13 +535,15 @@ u64 add_new_free_space(struct btrfs_block_group *block_group, u64 start, u64 end
 
 	if (start < end) {
 		size = end - start;
-		total_added += size;
 		ret = btrfs_add_free_space_async_trimmed(block_group, start,
 							 size);
-		BUG_ON(ret); /* -ENOMEM or logic error */
+		if (ret)
+			return ret;
+		if (total_added_ret)
+			*total_added_ret += size;
 	}
 
-	return total_added;
+	return 0;
 }
 
 /*
@@ -779,8 +787,13 @@ next:
 
 		if (key.type == BTRFS_EXTENT_ITEM_KEY ||
 		    key.type == BTRFS_METADATA_ITEM_KEY) {
-			total_found += add_new_free_space(block_group, last,
+			u64 space_added;
-							  key.objectid);
+
+			ret = add_new_free_space(block_group, last, key.objectid,
+						 &space_added);
+			if (ret)
+				goto out;
+			total_found += space_added;
 			if (key.type == BTRFS_METADATA_ITEM_KEY)
 				last = key.objectid +
 					fs_info->nodesize;
@@ -795,11 +808,10 @@ next:
 		}
 		path->slots[0]++;
 	}
-	ret = 0;
-
-	total_found += add_new_free_space(block_group, last,
-				block_group->start + block_group->length);
 
+	ret = add_new_free_space(block_group, last,
+				 block_group->start + block_group->length,
+				 NULL);
 out:
 	btrfs_free_path(path);
 	return ret;
@@ -2294,9 +2306,11 @@ static int read_one_block_group(struct btrfs_fs_info *info,
 		btrfs_free_excluded_extents(cache);
 	} else if (cache->used == 0) {
 		cache->cached = BTRFS_CACHE_FINISHED;
-		add_new_free_space(cache, cache->start,
+		ret = add_new_free_space(cache, cache->start,
-				   cache->start + cache->length);
+					 cache->start + cache->length, NULL);
 		btrfs_free_excluded_extents(cache);
+		if (ret)
+			goto error;
 	}
 
 	ret = btrfs_add_block_group_cache(info, cache);
@@ -2740,9 +2754,12 @@ struct btrfs_block_group *btrfs_make_block_group(struct btrfs_trans_handle *tran
 		return ERR_PTR(ret);
 	}
 
-	add_new_free_space(cache, chunk_offset, chunk_offset + size);
+	ret = add_new_free_space(cache, chunk_offset, chunk_offset + size, NULL);
-
 	btrfs_free_excluded_extents(cache);
+	if (ret) {
+		btrfs_put_block_group(cache);
+		return ERR_PTR(ret);
+	}
 
 	/*
 	 * Ensure the corresponding space_info object is created and

fs/btrfs/block-group.h

@@ -289,8 +289,8 @@ int btrfs_cache_block_group(struct btrfs_block_group *cache, bool wait);
 void btrfs_put_caching_control(struct btrfs_caching_control *ctl);
 struct btrfs_caching_control *btrfs_get_caching_control(
 		struct btrfs_block_group *cache);
-u64 add_new_free_space(struct btrfs_block_group *block_group,
+int add_new_free_space(struct btrfs_block_group *block_group,
-		       u64 start, u64 end);
+		       u64 start, u64 end, u64 *total_added_ret);
 struct btrfs_trans_handle *btrfs_start_trans_remove_block_group(
 				struct btrfs_fs_info *fs_info,
 				const u64 chunk_offset);

fs/btrfs/free-space-tree.c

@@ -1515,9 +1515,13 @@ static int load_free_space_bitmaps(struct btrfs_caching_control *caching_ctl,
 			if (prev_bit == 0 && bit == 1) {
 				extent_start = offset;
 			} else if (prev_bit == 1 && bit == 0) {
-				total_found += add_new_free_space(block_group,
+				u64 space_added;
-								  extent_start,
+
-								  offset);
+				ret = add_new_free_space(block_group, extent_start,
+							 offset, &space_added);
+				if (ret)
+					goto out;
+				total_found += space_added;
 				if (total_found > CACHING_CTL_WAKE_UP) {
 					total_found = 0;
 					wake_up(&caching_ctl->wait);
@@ -1529,8 +1533,9 @@ static int load_free_space_bitmaps(struct btrfs_caching_control *caching_ctl,
 		}
 	}
 	if (prev_bit == 1) {
-		total_found += add_new_free_space(block_group, extent_start,
+		ret = add_new_free_space(block_group, extent_start, end, NULL);
-						  end);
+		if (ret)
+			goto out;
 		extent_count++;
 	}
 
@@ -1569,6 +1574,8 @@ static int load_free_space_extents(struct btrfs_caching_control *caching_ctl,
 	end = block_group->start + block_group->length;
 
 	while (1) {
+		u64 space_added;
+
 		ret = btrfs_next_item(root, path);
 		if (ret < 0)
 			goto out;
@@ -1583,8 +1590,11 @@ static int load_free_space_extents(struct btrfs_caching_control *caching_ctl,
 		ASSERT(key.type == BTRFS_FREE_SPACE_EXTENT_KEY);
 		ASSERT(key.objectid < end && key.objectid + key.offset <= end);
 
-		total_found += add_new_free_space(block_group, key.objectid,
+		ret = add_new_free_space(block_group, key.objectid,
-						  key.objectid + key.offset);
+					 key.objectid + key.offset, &space_added);
+		if (ret)
+			goto out;
+		total_found += space_added;
 		if (total_found > CACHING_CTL_WAKE_UP) {
 			total_found = 0;
 			wake_up(&caching_ctl->wait);