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From:   "Huang, Ying" <ying.huang@intel.com>
To:     Miaohe Lin <linmiaohe@huawei.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>, <tim.c.chen@linux.intel.com>,
        <linux-kernel@vger.kernel.org>, <linux-mm@kvack.org>
Subject: Re: [PATCH 3/5] mm/swap_state: fix get_shadow_from_swap_cache()
 race with swapoff
References: <20210408130820.48233-1-linmiaohe@huawei.com>
        <20210408130820.48233-4-linmiaohe@huawei.com>
Date:   Tue, 13 Apr 2021 09:33:41 +0800
In-Reply-To: <20210408130820.48233-4-linmiaohe@huawei.com> (Miaohe Lin's
        message of "Thu, 8 Apr 2021 09:08:18 -0400")
Message-ID: <87im4rufwq.fsf@yhuang6-desk1.ccr.corp.intel.com>
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Miaohe Lin <linmiaohe@huawei.com> writes:

> The function get_shadow_from_swap_cache() can race with swapoff, though
> it's only called by do_swap_page() now.
>
> Fixes: aae466b0052e ("mm/swap: implement workingset detection for anonymous LRU")
> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>

This is unnecessary.  The only caller has guaranteed the swap device
from swapoff.

Best Regards,
Huang, Ying

> ---
>  mm/swap_state.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/mm/swap_state.c b/mm/swap_state.c
> index 272ea2108c9d..709c260d644a 100644
> --- a/mm/swap_state.c
> +++ b/mm/swap_state.c
> @@ -83,11 +83,14 @@ void show_swap_cache_info(void)
>  
>  void *get_shadow_from_swap_cache(swp_entry_t entry)
>  {
> -	struct address_space *address_space = swap_address_space(entry);
> -	pgoff_t idx = swp_offset(entry);
> +	struct swap_info_struct *si;
>  	struct page *page;
>  
> -	page = xa_load(&address_space->i_pages, idx);
> +	si = get_swap_device(entry);
> +	if (!si)
> +		return NULL;
> +	page = xa_load(&swap_address_space(entry)->i_pages, swp_offset(entry));
> +	put_swap_device(si);
>  	if (xa_is_value(page))
>  		return page;
>  	return NULL;