btrfs: use btrfs_find_first_inode() at btrfs_prune_dentries()

Currently btrfs_prune_dentries() has open code to find the first inode in
a root with a minimum inode number. Remove that code and make it use the
helper btrfs_find_first_inode() for that task.
Reviewed-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/inode.c

@@ -4416,64 +4416,26 @@ static noinline int may_destroy_subvol(struct btrfs_root *root)
 static void btrfs_prune_dentries(struct btrfs_root *root)
 {
 	struct btrfs_fs_info *fs_info = root->fs_info;
-	struct rb_node *node;
-	struct rb_node *prev;
-	struct btrfs_inode *entry;
-	struct inode *inode;
-	u64 objectid = 0;
+	struct btrfs_inode *inode;
+	u64 min_ino = 0;
 
 	if (!BTRFS_FS_ERROR(fs_info))
 		WARN_ON(btrfs_root_refs(&root->root_item) != 0);
 
-	spin_lock(&root->inode_lock);
-again:
-	node = root->inode_tree.rb_node;
-	prev = NULL;
-	while (node) {
-		prev = node;
-		entry = rb_entry(node, struct btrfs_inode, rb_node);
-
-		if (objectid < btrfs_ino(entry))
-			node = node->rb_left;
-		else if (objectid > btrfs_ino(entry))
-			node = node->rb_right;
-		else
-			break;
-	}
-	if (!node) {
-		while (prev) {
-			entry = rb_entry(prev, struct btrfs_inode, rb_node);
-			if (objectid <= btrfs_ino(entry)) {
-				node = prev;
-				break;
-			}
-			prev = rb_next(prev);
-		}
-	}
-	while (node) {
-		entry = rb_entry(node, struct btrfs_inode, rb_node);
-		objectid = btrfs_ino(entry) + 1;
-		inode = igrab(&entry->vfs_inode);
-		if (inode) {
-			spin_unlock(&root->inode_lock);
-			if (atomic_read(&inode->i_count) > 1)
-				d_prune_aliases(inode);
-			/*
-			 * btrfs_drop_inode will have it removed from the inode
-			 * cache when its usage count hits zero.
-			 */
-			iput(inode);
-			cond_resched();
-			spin_lock(&root->inode_lock);
-			goto again;
-		}
-
-		if (cond_resched_lock(&root->inode_lock))
-			goto again;
+	inode = btrfs_find_first_inode(root, min_ino);
+	while (inode) {
+		if (atomic_read(&inode->vfs_inode.i_count) > 1)
+			d_prune_aliases(&inode->vfs_inode);
 
-		node = rb_next(node);
+		min_ino = btrfs_ino(inode) + 1;
+		/*
+		 * btrfs_drop_inode() will have it removed from the inode
+		 * cache when its usage count hits zero.
+		 */
+		iput(&inode->vfs_inode);
+		cond_resched();
+		inode = btrfs_find_first_inode(root, min_ino);
 	}
-	spin_unlock(&root->inode_lock);
 }
 
 int btrfs_delete_subvolume(struct btrfs_inode *dir, struct dentry *dentry)