Many of them actually do provide guarantees (as e.g. evidenced that a typical implementation of an x86 memory barrier is an "lock; addl $0,0(%%rsp)"). That's wh

Many of them actually do provide guarantees (as e.g. evidenced that a typical implementation of an x86 memory barrier is an "lock; addl $0,0(%%rsp)"). That's why there's now stuff like __smp_mb__before_atomic()/__smp_mb__after_atomic(), to avoid unnecessary atomic ops.