linux-kernel - Re: [PATCH] mm: fix a data race in put

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Date:   Thu, 6 Feb 2020 10:23:31 -0500
From:   Qian Cai <cai@....pw>
To:     Jan Kara <jack@...e.cz>
Cc:     David Hildenbrand <david@...hat.com>, akpm@...ux-foundation.org,
        jhubbard@...dia.com, ira.weiny@...el.com, dan.j.williams@...el.com,
        elver@...gle.com, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: fix a data race in put_page()



> On Feb 6, 2020, at 9:55 AM, Jan Kara <jack@...e.cz> wrote:
> 
> I don't think the problem is real. The question is how to make KCSAN happy
> in a way that doesn't silence other possibly useful things it can find and
> also which makes it most obvious to the reader what's going on... IMHO
> using READ_ONCE() fulfills these targets nicely - it is free
> performance-wise in this case, it silences the checker without impacting
> other races on page->flags, its kind of obvious we don't want the load torn
> in this case so it makes sense to the reader (although a comment may be
> nice).

Actually, use the data_race() macro there fulfilling the same purpose too, i.e, silence the splat here but still keep searching for other races.