Re: KCSAN: data-race in __alloc_file / __alloc_file

[Linus Torvalds]

On Mon, Nov 11, 2019 at 12:43 PM Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> Yeah, maybe we could have some model for marking "this is statistics,
> doesn't need to be exact".

Side note: that marking MUST NOT be "READ_ONCE + WRITE_ONCE", because
that makes gcc create horrible code, and only makes the race worse.

At least with a regular add, it might stay as a single r-m-w
instruction on architectures that have that, and makes the quality of
the statistics slightly better (no preemption etc).

So that's an excellent example of where changing code to use
WRITE_ONCE actually makes the code objectively worse in practice -
even if it might be the same in theory.

                Linus