Re: racy acccess in kern_runq.c

[Mindaugas Rasiukevicius <rmind%netbsd.org@localhost>]

Maxime Villard <max%m00nbsd.net@localhost> wrote:
> Le 06/12/2019 à 17:53, Andrew Doran a écrit :
> > On Fri, Dec 06, 2019 at 05:22:39PM +0900, Kengo NAKAHARA wrote:
> > 
> >>   	/* Update the worker */
> >> -	worker_ci = hci;
> >> +	atomic_swap_ptr(&worker_ci, hci);
> > 
> > Why atomic_swap_ptr() not atomic_store_relaxed()?  I don't see any bug
> > that it fixes.  Other than that it look OK to me.
> 
> Because I suggested it; my concern was that if not explicitly atomic, the
> cpu could make two writes internally (even though the compiler produces
> only one instruction), and in that case a page fault would have been
> possible because of garbage dereference.

No, atomic_store_relaxed() is sufficient; that is what it is for.

-- 
Mindaugas