On Fri, Jun 19, 2020 at 10:48:02AM -0700, Paul E. McKenney wrote: > On Fri, Jun 19, 2020 at 10:20:47AM -0700, Paul E. McKenney wrote:
> > > @@ -2615,7 +2617,8 @@ try_to_wake_up(struct task_struct *p, unsigned int > > > state, int wake_flags) > > > * let the waker make forward progress. This is safe because IRQs are > > > * disabled and the IPI will deliver after on_cpu is cleared. > > > */ > > > - if (READ_ONCE(p->on_cpu) && ttwu_queue_wakelist(p, cpu, wake_flags | > > > WF_ON_RQ)) > > > + if (smp_load_acquire(&p->on_cpu) && > > Given the x86 memory model, this only protects against the compiler > reordering accesses in ttwu_queue_wakelist() against the fetch of > p->on_cpu, correct? Yes. > Don't get me wrong, I do see some potential compiler misorderings, > including with cpu_rq(cpu)->nr_running. Just curious. Given this is arch independent code, I'd better write generic code, and there I really think this wants to be acquire. I'll also try and write a comment for next time.
