Concurrency Problem in Double Check Locking

Consider the LazyInit class shown below, which uses a double-check locking pattern to lazily initialize a Resource object. Which of the following statements best describes a potential concurrency problem in this implementation?

public class LazyInit {
    private Resource resource = null;
    
    public Resource getResource() {
        if(resource == null) {
            synchronized(this) {
                if(resource == null) {
                    resource = new Resource();
                }
            }
        }
        return resource;
    }
}

class Resource {
    // Resource implementation
}