linux-kernel - Re: [PATCH -mm -V2] mm, swap: Fix false error message in __swp

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Date:   Mon, 30 Oct 2017 09:02:30 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Minchan Kim <minchan@...nel.org>
Cc:     "Huang, Ying" <ying.huang@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Huang Ying <huang.ying.caritas@...il.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>, stable@...r.kernel.org,
        Christian Kujau <lists@...dbynature.de>
Subject: Re: [PATCH -mm -V2] mm, swap: Fix false error message in
 __swp_swapcount()

On Mon 30-10-17 08:57:13, Minchan Kim wrote:
[...]
> Although it's better than old, we can make it simple, still.
> 
> diff --git a/include/linux/swapops.h b/include/linux/swapops.h
> index 291c4b534658..f50d5a48f03a 100644
> --- a/include/linux/swapops.h
> +++ b/include/linux/swapops.h
> @@ -41,6 +41,13 @@ static inline unsigned swp_type(swp_entry_t entry)
>  	return (entry.val >> SWP_TYPE_SHIFT(entry));
>  }
>  
> +extern struct swap_info_struct *swap_info[];
> +
> +static inline struct swap_info_struct *swp_si(swp_entry_t entry)
> +{
> +	return swap_info[swp_type(entry)];
> +}
> +
>  /*
>   * Extract the `offset' field from a swp_entry_t.  The swp_entry_t is in
>   * arch-independent format
> diff --git a/mm/swap_state.c b/mm/swap_state.c
> index 378262d3a197..a0fe2d54ad09 100644
> --- a/mm/swap_state.c
> +++ b/mm/swap_state.c
> @@ -554,6 +554,7 @@ struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
>  			struct vm_area_struct *vma, unsigned long addr)
>  {
>  	struct page *page;
> +	struct swap_info_struct *si = swp_si(entry);

Aren't you accessing beyond the array here?

>  	unsigned long entry_offset = swp_offset(entry);
>  	unsigned long offset = entry_offset;
>  	unsigned long start_offset, end_offset;
> @@ -572,6 +573,9 @@ struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
>  	if (!start_offset)	/* First page is swap header. */
>  		start_offset++;
>  
> +	if (end_offset >= si->max)
> +		end_offset = si->max - 1;
> +
>  	blk_start_plug(&plug);
>  	for (offset = start_offset; offset <= end_offset ; offset++) {
>  		/* Ok, do the async read-ahead now */

-- 
Michal Hocko
SUSE Labs