linux-kernel - Re: [PATCH -next] mm/page_counter: mark intentional data races

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Message-Id: <9507ADF5-1040-495E-9A39-C0C23412AD64@lca.pw>
Date:   Wed, 29 Jan 2020 04:51:58 -0500
From:   Qian Cai <cai@....pw>
To:     Marco Elver <elver@...gle.com>
Cc:     Michal Hocko <mhocko@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -next] mm/page_counter: mark intentional data races



> On Jan 29, 2020, at 4:06 AM, Marco Elver <elver@...gle.com> wrote:
> 
> These should be using 'READ_ONCE' and 'WRITE_ONCE' for c->watermark.
> Store or load tearing would change the logic here, since the
> comparison might see garbage.

I originally thought that it probably does not matter because it is racy there by doing lockless access anyway. Another thread could change the value at anytime.

Now, I agree set it to a garbage due to a data race could be quite unpleasant there.