struct dentry *d_ancestor(struct dentry *p1, struct dentry *p2)
{
	struct dentry *p;

	for (p = p2; !IS_ROOT(p); p = p->d_parent) {
		if (p->d_parent == p1)
			return p;
	}
	return NULL;
}

The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently.