On Fri, 16 Aug 2019, Mathieu Desnoyers wrote: > If you choose not to use READ_ONCE(), then the "load tearing" issue can > cause similar spurious 1 -> 0 -> 1 transitions near 16-bit counter > overflow as described above. The "Invented load" also becomes an issue, > because the compiler could use the loaded value for a branch, and re-load > that value between two branches which are expected to use the same value, > effectively generating a corrupted state. > > I think we need a statement about whether READ_ONCE/WRITE_ONCE should > be used in this kind of situation, or if we are fine dealing with the > awkward compiler side-effects when they will occur.
The only real downside (apart from readability) of READ_ONCE and WRITE_ONCE is that they prevent the compiler from optimizing accesses to the location being read or written. But if you're just doing a single access in each place, not multiple accesses, then there's nothing to optimize anyway. So there's no real reason not to use READ_ONCE or WRITE_ONCE. Alan Stern
