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From:   "Huang, Ying" <ying.huang@intel.com>
To:     Tim Chen <tim.c.chen@linux.intel.com>
Cc:     Miaohe Lin <linmiaohe@huawei.com>, <akpm@linux-foundation.org>,
        <hannes@cmpxchg.org>, <mhocko@suse.com>, <iamjoonsoo.kim@lge.com>,
        <vbabka@suse.cz>, <alex.shi@linux.alibaba.com>,
        <willy@infradead.org>, <minchan@kernel.org>,
        <richard.weiyang@gmail.com>, <hughd@google.com>,
        <linux-kernel@vger.kernel.org>, <linux-mm@kvack.org>
Subject: Re: [PATCH 2/5] swap: fix do_swap_page() race with swapoff
References: <20210408130820.48233-1-linmiaohe@huawei.com>
        <20210408130820.48233-3-linmiaohe@huawei.com>
        <87o8ejug76.fsf@yhuang6-desk1.ccr.corp.intel.com>
        <c9bb0a8a-72ca-d9b4-4c31-d4d8cfde0b4c@linux.intel.com>
Date:   Wed, 14 Apr 2021 09:04:05 +0800
In-Reply-To: <c9bb0a8a-72ca-d9b4-4c31-d4d8cfde0b4c@linux.intel.com> (Tim
        Chen's message of "Tue, 13 Apr 2021 12:24:15 -0700")
Message-ID: <878s5lu16i.fsf@yhuang6-desk1.ccr.corp.intel.com>
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Tim Chen <tim.c.chen@linux.intel.com> writes:

> On 4/12/21 6:27 PM, Huang, Ying wrote:
>
>> 
>> This isn't the commit that introduces the race.  You can use `git blame`
>> find out the correct commit.  For this it's commit 0bcac06f27d7 "mm,
>> swap: skip swapcache for swapin of synchronous device".
>> 
>> And I suggest to merge 1/5 and 2/5 to make it easy to get the full
>> picture.
>
> I'll suggest make fix to do_swap_page race with get/put_swap_device
> as a first patch. Then the per_cpu_ref stuff in patch 1 and patch 2 can
> be combined together.

The original get/put_swap_device() use rcu_read_lock/unlock().  I don't
think it's good to wrap swap_read_page() with it.  After all, some
complex operations are done in swap_read_page(), including
blk_io_schedule().

Best Regards,
Huang, Ying