From: Qian Cai <cai@lca.pw>
To: Jan Kara <jack@suse.cz>
Cc: John Hubbard <jhubbard@nvidia.com>,
akpm@linux-foundation.org, ira.weiny@intel.com,
dan.j.williams@intel.com, linux-mm@kvack.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH -next] mm: mark a intentional data race in page_zonenum()
Date: Thu, 6 Feb 2020 06:14:55 -0500 [thread overview]
Message-ID: <3E1FB0B8-F499-45F7-9B03-7B80395FFF19@lca.pw> (raw)
In-Reply-To: <20200206090436.GF14001@quack2.suse.cz>
> On Feb 6, 2020, at 4:04 AM, Jan Kara <jack@suse.cz> wrote:
>
> So in this particular case, store tearing is non-issue because we use
> atomic operation to store the value in page_cpupid_xchg_last(). I think it
> would make some sense to use READ_ONCE(page->flags) here to prevent
> compiler from loading page->flags several times - I have hard time finding
> a reason why a compiler would want to do that but conceptually that
> protection makes sense, it is for free performance wise, and will still
> allow KCSAN to find a race in case we ever grow a place that modifies
> page's zone non-atomically (which might be a real problem). And it should
> also silence the KCSAN warning AFAIU.
Ah, read up to 3 bits might be an issue then. I’ll post an alternative version which uses READ_ONCE() just for the old page ( because the new page has not been published yet) in wp_page_copy() then.
next prev parent reply other threads:[~2020-02-06 11:15 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-06 3:52 [PATCH -next] mm: mark a intentional data race in page_zonenum() Qian Cai
2020-02-06 4:50 ` John Hubbard
2020-02-06 9:04 ` Jan Kara
2020-02-06 11:14 ` Qian Cai [this message]
2020-02-06 14:01 ` Qian Cai
2020-02-06 14:01 ` Qian Cai
2020-02-06 14:35 ` Marco Elver
2020-02-06 14:35 ` Marco Elver
2020-02-06 23:18 ` John Hubbard
2020-02-07 13:18 ` Marco Elver
2020-02-07 13:18 ` Marco Elver
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