Re: KCSAN: data-race in __alloc_file / __alloc_file

[Eric Dumazet]

On Fri, Nov 8, 2019 at 9:53 AM Eric Dumazet <edumazet@xxxxxxxxxx> wrote:
>
> On Fri, Nov 8, 2019 at 9:39 AM Linus Torvalds
> <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> > I'd hope that there is some way to mark the cases we know about where
> > we just have a flag. I'm not sure what KCSAN uses right now - is it
> > just the "volatile" that makes KCSAN ignore it, or are there other
> > ways to do it?
>
> I dunno, Marco will comment on this.
>
> I personally like WRITE_ONCE() since it adds zero overhead on generated code,
> and is the facto accessor we used for many years (before KCSAN was conceived)
>

BTW, I would love an efficient ADD_ONCE(variable, value)

Using WRITE_ONCE(variable, variable + value) is not good, since it can
not use the
optimized instructions operating directly on memory.