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From:   "Huang, Ying" <ying.huang@intel.com>
To:     Matthew Wilcox <willy@infradead.org>
Cc:     Hugh Dickins <hughd@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        David Hildenbrand <david@redhat.com>,
        Yang Shi <shy828301@gmail.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, Miaohe Lin <linmiaohe@huawei.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@suse.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Minchan Kim <minchan@kernel.org>
Subject: Re: [PATCH] mm,shmem: Fix a typo in shmem_swapin_page()
References: <20210723080000.93953-1-ying.huang@intel.com>
        <24187e5e-069-9f3f-cefe-39ac70783753@google.com>
        <YPs6cQo7iG1JcOn8@casper.infradead.org>
        <8735rr54i9.fsf@yhuang6-desk2.ccr.corp.intel.com>
        <YQkwBdpWTPjv4xIx@casper.infradead.org>
Date:   Wed, 04 Aug 2021 17:01:39 +0800
In-Reply-To: <YQkwBdpWTPjv4xIx@casper.infradead.org> (Matthew Wilcox's message
        of "Tue, 3 Aug 2021 13:01:09 +0100")
Message-ID: <87czqt4m8c.fsf@yhuang6-desk2.ccr.corp.intel.com>
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Matthew Wilcox <willy@infradead.org> writes:

> On Tue, Aug 03, 2021 at 04:14:38PM +0800, Huang, Ying wrote:
>> Matthew Wilcox <willy@infradead.org> writes:
>> > But I REALLY REALLY REALLY want a reproducer.  Right now, I have a hard
>> > time believing this, or any of the other races can really happen.
>> 
>> I think the race is only theoretical too.  Firstly, swapoff is a rare
>> operations in practice; secondly, the race window is really small.
>
> So do something to provoke it.  Widen the window.  Put an msleep(1000)
> between *pagep = NULL and the call to get_swap_device().  That's assuming
> that the swapon/swapoff loop that I proposed doesn't work.  Did you
> try it?

I haven't tried it.  Do you agree that the race is possible in theory?
But if you still really want it, I can try to do that.

Best Regards,
Huang, Ying