linux-kernel - Re: [PATCH 3/3] mm/swapfile: fix possible data races of inuse

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Date:   Tue, 31 May 2022 15:02:24 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Miaohe Lin <linmiaohe@...wei.com>, akpm@...ux-foundation.org
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] mm/swapfile: fix possible data races of inuse_pages

On 27.05.22 11:26, Miaohe Lin wrote:
> si->inuse_pages could still be accessed concurrently now. The plain reads
> outside si->lock critical section, i.e. swap_show and si_swapinfo, which
> results in data races. But these should be ok because they're just used
> for showing swap info.
> 
> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
> ---
>  mm/swapfile.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index e033a53a99df..29d7ca9eaa3c 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -2649,7 +2649,7 @@ static int swap_show(struct seq_file *swap, void *v)
>  	}
>  
>  	bytes = si->pages << (PAGE_SHIFT - 10);
> -	inuse = si->inuse_pages << (PAGE_SHIFT - 10);
> +	inuse = READ_ONCE(si->inuse_pages) << (PAGE_SHIFT - 10);
>  
>  	file = si->swap_file;
>  	len = seq_file_path(swap, file, " \t\n\\");
> @@ -3268,7 +3268,7 @@ void si_swapinfo(struct sysinfo *val)
>  		struct swap_info_struct *si = swap_info[type];
>  
>  		if ((si->flags & SWP_USED) && !(si->flags & SWP_WRITEOK))
> -			nr_to_be_unused += si->inuse_pages;
> +			nr_to_be_unused += READ_ONCE(si->inuse_pages);
>  	}
>  	val->freeswap = atomic_long_read(&nr_swap_pages) + nr_to_be_unused;
>  	val->totalswap = total_swap_pages + nr_to_be_unused;


AFAIKT, this makes sense

Reviewed-by: David Hildenbrand <david@...hat.com>

-- 
Thanks,

David / dhildenb