btrfs: Don't BUG_ON alloc_path errors in find_next_chunk

I also removed the BUG_ON from error return of find_next_chunk in
init_first_rw_device(). It turns out that the only caller of
init_first_rw_device() also BUGS on any nonzero return so no actual behavior
change has occurred here.

do_chunk_alloc() also needed an update since it calls btrfs_alloc_chunk()
which can now return -ENOMEM. Instead of setting space_info->full on any
error from btrfs_alloc_chunk() I catch and return every error value _except_
-ENOSPC. Thanks goes to Tsutomu Itoh for pointing that issue out.

Signed-off-by: Mark Fasheh <mfasheh@suse.com>

fs/btrfs/extent-tree.c

@@ -3277,6 +3277,9 @@ again:
 	}
 
 	ret = btrfs_alloc_chunk(trans, extent_root, flags);
+	if (ret < 0 && ret != -ENOSPC)
+		goto out;
+
 	spin_lock(&space_info->lock);
 	if (ret)
 		space_info->full = 1;
@@ -3286,6 +3289,7 @@ again:
 	space_info->force_alloc = CHUNK_ALLOC_NO_FORCE;
 	space_info->chunk_alloc = 0;
 	spin_unlock(&space_info->lock);
+out:
 	mutex_unlock(&extent_root->fs_info->chunk_mutex);
 	return ret;
 }

fs/btrfs/volumes.c

@@ -1037,7 +1037,8 @@ static noinline int find_next_chunk(struct btrfs_root *root,
 	struct btrfs_key found_key;
 
 	path = btrfs_alloc_path();
-	BUG_ON(!path);
+	if (!path)
+		return -ENOMEM;
 
 	key.objectid = objectid;
 	key.offset = (u64)-1;
@@ -2663,7 +2664,8 @@ static noinline int init_first_rw_device(struct btrfs_trans_handle *trans,
 
 	ret = find_next_chunk(fs_info->chunk_root,
 			      BTRFS_FIRST_CHUNK_TREE_OBJECTID, &chunk_offset);
-	BUG_ON(ret);
+	if (ret)
+		return ret;
 
 	alloc_profile = BTRFS_BLOCK_GROUP_METADATA |
 			(fs_info->metadata_alloc_profile &