From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
To: Qian Cai <cai@lca.pw>, Dmitry Vyukov <dvyukov@google.com>
Cc: Michal Hocko <mhocko@kernel.org>,
akpm@linux-foundation.org, hannes@cmpxchg.org, elver@google.com,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm/page_counter: fix various data races
Date: Wed, 29 Jan 2020 21:13:37 +0900 [thread overview]
Message-ID: <59f892d0-5fc4-ae32-ce65-5a688d9180c8@I-love.SAKURA.ne.jp> (raw)
In-Reply-To: <20200129120302.GJ24244@dhcp22.suse.cz>
On 2020/01/29 21:03, Michal Hocko wrote:
>> Fixes: 3e32cb2e0a12 ("mm: memcontrol: lockless page counters")
>> Signed-off-by: Qian Cai <cai@lca.pw>
>
> Acked-by: Michal Hocko <mhocko@suse.com>
Please include
Reported-by: syzbot+f36cfe60b1006a94f9dc@syzkaller.appspotmail.com
for https://syzkaller.appspot.com/bug?id=744097b8b91cecd8b035a6f746bb12e4efc7669f .
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.
>
>> ---
>> mm/page_counter.c | 8 ++++----
>> 1 file changed, 4 insertions(+), 4 deletions(-)
>>
>> diff --git a/mm/page_counter.c b/mm/page_counter.c
>> index de31470655f6..a17841150906 100644
>> --- a/mm/page_counter.c
>> +++ b/mm/page_counter.c
>> @@ -82,8 +82,8 @@ void page_counter_charge(struct page_counter *counter, unsigned long nr_pages)
>> * This is indeed racy, but we can live with some
>> * inaccuracy in the watermark.
>> */
>> - if (new > c->watermark)
>> - c->watermark = new;
>> + if (new > READ_ONCE(c->watermark))
>> + WRITE_ONCE(c->watermark, new);
>> }
>> }
>>
>> @@ -135,8 +135,8 @@ bool page_counter_try_charge(struct page_counter *counter,
>> * Just like with failcnt, we can live with some
>> * inaccuracy in the watermark.
>> */
>> - if (new > c->watermark)
>> - c->watermark = new;
>> + if (new > READ_ONCE(c->watermark))
>> + WRITE_ONCE(c->watermark, new);
>> }
>> return true;
>>
>> --
>> 2.21.0 (Apple Git-122.2)
>
next prev parent reply other threads:[~2020-01-29 12:13 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-29 10:52 [PATCH] mm/page_counter: fix various data races 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 [this message]
2020-01-29 12:21 ` Marco Elver
2020-01-29 13:47 ` Tetsuo Handa
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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