Re: [patch 2/4 v3]swap: __swap_duplicate check bad swap entry

[Rafael Aquini <aquini@redhat.com>]

On Thu, Feb 21, 2013 at 10:22:19AM +0800, Shaohua Li wrote:
> Sorry if you receive this one twice, last mail get mail address messed.
> 
> In swapin_readahead(), read_swap_cache_async() can read a bad swap entry,
> because we don't check if readahead swap entry is bad. This doesn't break
> anything but such swapin page is wasteful and can only be freed at page
> reclaim. We avoid read such swap entry.
> 

Acked-by: Rafael Aquini <aquini@redhat.com>


> And next patch will mark a swap entry bad temporarily for discard. Without this
> patch, swap entry count will be messed.
> 
> Thanks Hugh to inspire swapin_readahead could use bad swap entry.
> 
> Signed-off-by: Shaohua Li <shli@fusionio.com>
> ---
>  mm/swapfile.c |    5 +++++
>  1 file changed, 5 insertions(+)
> 
> Index: linux/mm/swapfile.c
> ===================================================================
> --- linux.orig/mm/swapfile.c	2013-02-18 15:21:09.285317914 +0800
> +++ linux/mm/swapfile.c	2013-02-18 15:21:34.545004083 +0800
> @@ -2374,6 +2374,11 @@ static int __swap_duplicate(swp_entry_t
>  		goto unlock_out;
>  
>  	count = p->swap_map[offset];
> +	if (unlikely(swap_count(count) == SWAP_MAP_BAD)) {
> +		err = -ENOENT;
> +		goto unlock_out;
> +	}
> +
>  	has_cache = count & SWAP_HAS_CACHE;
>  	count &= ~SWAP_HAS_CACHE;
>  	err = 0;
> 
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