Re: [PATCH] tracefs/eventfs: Use root and instance inodes as default ownership

[Al Viro]

On Wed, Jan 03, 2024 at 08:32:46PM -0500, Steven Rostedt wrote:

> +static struct inode *instance_inode(struct dentry *parent, struct inode 
> *inode)
> +{
> +     struct tracefs_inode *ti;
> +     struct inode *root_inode;
> +
> +     root_inode = d_inode(inode->i_sb->s_root);
> +
> +     /* If parent is NULL then use root inode */
> +     if (!parent)
> +             return root_inode;
> +
> +     /* Find the inode that is flagged as an instance or the root inode */
> +     do {
> +             inode = d_inode(parent);
> +             if (inode == root_inode)
> +                     return root_inode;
> +
> +             ti = get_tracefs(inode);
> +
> +             if (ti->flags & TRACEFS_INSTANCE_INODE)
> +                     return inode;
> +     } while ((parent = parent->d_parent));

*blink*

This is equivalent to
                ...
                parent = parent->d_parent;
        } while (true);

->d_parent is *never* NULL.  And what the hell is that loop supposed to do,
anyway?  Find the nearest ancestor tagged with TRACEFS_INSTANCE_INODE?

If root is not marked that way, I would suggest
        if (!parent)
                parent = inode->i_sb->s_root;
        while (!IS_ROOT(parent)) {
                struct tracefs_inode *ti = get_tracefs(parent->d_inode);
                if (ti->flags & TRACEFS_INSTANCE_INODE)
                        break;
                parent = parent->d_parent;
        }
        return parent->d_inode;