>>>The problem is that a reader should not do anything with the data that is read, which depends on its value, before validating the copy, by counter comparison

>>>The problem is that a reader should not do anything with the data that is read, which depends on its value, before validating the copy, by counter comparison. The description of the problem explicitly says that this is not happening. The data is being thrown away if the counter comparison fails. So the only undefined behavior that I can think they might be referring to is the act of loading the data itself, even though it is thrown away if it is wrong. Is that what they mean?