Re: KCSAN: data-race in __alloc_file / __alloc_file

[Eric Dumazet]

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)

>
> "volatile" has huge problems with code generation for gcc. It would
> probably be fine for "not_rcu" in this case, but I'd like to avoid it
> in general otherwise, which is why I wonder if there are other
> options.
>
> But worst comes to worst, I'd be ok with a WRITE_ONCE() and a comment
> about why (and the reason being KCSAN, not the questionable
> optimization).

Ok for a single WRITE_ONCE() with a comment.

Hmm, which questionable optimization are you referring to?