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Subject: Re: [PATCH 2/5] swap: fix do_swap_page() race with swapoff
To:     Tim Chen <tim.c.chen@linux.intel.com>,
        "Huang, Ying" <ying.huang@intel.com>
CC:     <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>
References: <20210408130820.48233-1-linmiaohe@huawei.com>
 <20210408130820.48233-3-linmiaohe@huawei.com>
 <87o8ejug76.fsf@yhuang6-desk1.ccr.corp.intel.com>
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 <878s5lu16i.fsf@yhuang6-desk1.ccr.corp.intel.com>
 <7ce9d6a2-6a9a-1203-0566-8a3bf478876f@linux.intel.com>
From:   Miaohe Lin <linmiaohe@huawei.com>
Message-ID: <b652e6a6-0f4f-27d1-0a5e-6b86676ca08e@huawei.com>
Date:   Thu, 15 Apr 2021 11:19:34 +0800
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On 2021/4/15 0:13, Tim Chen wrote:
> 
> 
> On 4/13/21 6:04 PM, Huang, Ying wrote:
>> 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().
>>
> 
> In that case then have the patches to make get/put_swap_device to use
> percpu_ref first.  And the patch to to fix the race in do_swap_page
> later in another patch.
> 
> Patch 2 is mixing the two.
> 

Looks like a good way to organize this patch series. Many thanks!

> Tim
> .
>