How to miscompile programs with "benign" data races [pdf]

Go read section 2.4.

Section 2.4 gives a concrete example, though there are some asterisks. The example is one where a compiler rewrites something like `while (...) x++;` to put `x` in a register: `int reg = x; while (...) reg++; x = reg`. The author reports this is an optimization GCC was observed doing, and means you can have a read-writeback even when the while condition is false to begin with. If this optimization appears interleaved with identical writes then you have problems.