linux-kernel - Re: [PATCH 3/5] mm/swap_state: fix get_shadow_from_swap

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Date:   Wed, 14 Apr 2021 10:42:38 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     "Huang, Ying" <ying.huang@...el.com>
CC:     <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>, <tim.c.chen@...ux.intel.com>,
        <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>
Subject: Re: [PATCH 3/5] mm/swap_state: fix get_shadow_from_swap_cache() race
 with swapoff

On 2021/4/13 9:33, Huang, Ying wrote:
> Miaohe Lin <linmiaohe@...wei.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@...wei.com>
> 
> This is unnecessary.  The only caller has guaranteed the swap device
> from swapoff

Ok. This patch is just in case get_shadow_from_swap_cache() would be
called from elsewhere someday.

It's unnecessary and can be dropped now

.
> 
> 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;
> 
> .
>