From: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
To: Marco Elver <elver@google.com>
Cc: Qian Cai <cai@lca.pw>, Dmitry Vyukov <dvyukov@google.com>,
Michal Hocko <mhocko@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Johannes Weiner <hannes@cmpxchg.org>,
Linux Memory Management List <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] mm/page_counter: fix various data races
Date: Wed, 29 Jan 2020 22:47:45 +0900 [thread overview]
Message-ID: <9575c1cc-1669-9492-d657-ad4ba6494e88@i-love.sakura.ne.jp> (raw)
In-Reply-To: <CANpmjNOdFsU9gg7FSv7Pue0L2eAQ+5UHHaz9bgZ83r94prA4vQ@mail.gmail.com>
On 2020/01/29 21:21, Marco Elver wrote:
>> By the way, can READ_ONCE()/WRITE_ONCE() really solve this warning?
>> The link above says read/write on the same location ( mm/page_counter.c:129 ).
>> I don't know how READ_ONCE()/WRITE_ONCE() can solve the race.
>
> It avoids the *data* race, with *_ONCE telling the compiler to not
> optimize the accesses in concurrency-unfriendly ways. Since *_ONCE is
> used, it conveys clear intent that the code here is meant to be
> concurrent, and KCSAN stops complaining (and assumes that the *logic*
> is correct).
I see. Unlike c->failcnt++ which involves read-modify-write, *_ONCE() can be used for
simple read (like c->watermark) or simple write (like c->watermark = new) case.
next prev parent reply other threads:[~2020-01-29 13:48 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-29 10:52 Qian Cai
2020-01-29 10:57 ` David Hildenbrand
2020-01-29 10:58 ` David Hildenbrand
2020-01-29 12:03 ` Michal Hocko
2020-01-29 12:13 ` Tetsuo Handa
2020-01-29 12:21 ` Marco Elver
2020-01-29 13:47 ` Tetsuo Handa [this message]
2020-01-29 12:25 ` Qian Cai
2020-01-29 13:09 ` Tetsuo Handa
2020-02-11 12:14 ` Qian Cai
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