Re: [PATCH] zram: unsafe zram_get_element call in zram_read_page()

[Sergey Senozhatsky]

On (23/11/06 22:54), Vasily Averin wrote:
> @@ -1362,14 +1362,14 @@ static int zram_read_page(struct zram *zram, struct page *page, u32 index,
>  		ret = zram_read_from_zspool(zram, page, index);
>  		zram_slot_unlock(zram, index);
>  	} else {
> +		unsigned long entry = zram_get_element(zram, index);
>  		/*
>  		 * The slot should be unlocked before reading from the backing
>  		 * device.
>  		 */
>  		zram_slot_unlock(zram, index);
>  
> -		ret = read_from_bdev(zram, page, zram_get_element(zram, index),
> -				     parent);
> +		ret = read_from_bdev(zram, page, entry, parent);

Hmmm,
We may want to do more here. Basically, we probably need to re-confirm
after read_from_bdev() that the entry at index still has ZRAM_WB set
and, if so, that it points to the same blk_idx. IOW, check that it has
not been free-ed and re-used under us.

Minchan, what do you think? Is that scenario possible?