[$] The search for the correct amount of split-lock misery

Unlike many other architectures, x86 systems support atomic operations thataffect more than one cache line. This support comes at a cost, though, interms of overall system performance and, even, security. Over the last fewyears, kernel developers have worked to discourage the use of this sort of"split-lock" operation. Now, though, one group of users is feelinga little too discouraged, leading to a discussion of how much misery canappropriately be inflicted upon users who use problematic butarchitecturally legal operations.