On Tue, Aug 11, 2020 at 09:14:02AM +0200, Oleg Nesterov wrote:
> On 08/11, Peter Zijlstra wrote:
> >
> > On Tue, Aug 11, 2020 at 08:45:16AM +0200, Oleg Nesterov wrote:
> > >
> > > ->jobctl is always modified with ->siglock held, do we really need
> > > WRITE_ONCE() ?
> >
> > In theory, yes. The compiler doesn't know about locks, it can tear
> > writes whenever it feels like it.
>
> Yes, but why does this matter? Could you spell please?
Ah, well, that I don't konw. Why do we need the READ_ONCE() ?
It does:
> + if (!(task->jobctl & JOBCTL_TASK_WORK) &&
> + lock_task_sighand(task, &flags)) {
and the lock_task_sighand() implies barrier(), so I thought the reason
for the READ_ONCE() was load-tearing, and then we need WRITE_ONCE() to
avoid store-tearing.
