Re: [PATCH 1/3] sched, timer: Remove usages of ACCESS_ONCE in the scheduler

Jason Low
2015-04-15T02:12:46Z

Hi Steven,

On Tue, 2015-04-14 at 19:59 -0400, Steven Rostedt wrote:
> On Tue, 14 Apr 2015 16:09:44 -0700
> Jason Low <jason.low2@hp.com> wrote:
>
>
> > @@ -2088,7 +2088,7 @@ void task_numa_fault(int last_cpupid, int mem_node, int pages, int flags)
> >
> > static void reset_ptenuma_scan(struct task_struct *p)
> > {
> > - ACCESS_ONCE(p->mm->numa_scan_seq)++;
> > + WRITE_ONCE(p->mm->numa_scan_seq, READ_ONCE(p->mm->numa_scan_seq) + 1);
>
> Is the READ_ONCE() inside the WRITE_ONCE() really necessary?

Yeah, I think so to be safe, otherwise, the access of
p->mm->numa_scan_seq in the 2nd parameter doesn't have the volatile
cast.