linux-kernel - Re: [PATCH 2/5] swap: fix do_swap

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Message-ID: <878s5lu16i.fsf@yhuang6-desk1.ccr.corp.intel.com>
Date:   Wed, 14 Apr 2021 09:04:05 +0800
From:   "Huang, Ying" <ying.huang@...el.com>
To:     Tim Chen <tim.c.chen@...ux.intel.com>
Cc:     Miaohe Lin <linmiaohe@...wei.com>, <akpm@...ux-foundation.org>,
        <hannes@...xchg.org>, <mhocko@...e.com>, <iamjoonsoo.kim@....com>,
        <vbabka@...e.cz>, <alex.shi@...ux.alibaba.com>,
        <willy@...radead.org>, <minchan@...nel.org>,
        <richard.weiyang@...il.com>, <hughd@...gle.com>,
        <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>
Subject: Re: [PATCH 2/5] swap: fix do_swap_page() race with swapoff

Tim Chen <tim.c.chen@...ux.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