Re: [PATCH] zsmalloc: fix linking bug in init_zspage

[Minchan Kim]

Hi,

On Thu, Aug 09, 2018 at 08:28:17PM -0400, zhouxianrong wrote:
> From: zhouxianrong <zhouxianrong@xxxxxxxxxx>
> 
> The last partial object in last subpage of zspage should not be linked
> in allocation list. Otherwise it could trigger BUG_ON explicitly at
> function zs_map_object. But it happened rarely.

Could you be more specific? What case did you see the problem?
Is it a real problem or one founded by review?

Thanks.

> 
> Signed-off-by: zhouxianrong <zhouxianrong@xxxxxxxxxx>
> ---
>  mm/zsmalloc.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> index 8d87e973a4f5..24dd8da0aa59 100644
> --- a/mm/zsmalloc.c
> +++ b/mm/zsmalloc.c
> @@ -1040,6 +1040,8 @@ static void init_zspage(struct size_class *class, struct zspage *zspage)
>  			 * Reset OBJ_TAG_BITS bit to last link to tell
>  			 * whether it's allocated object or not.
>  			 */
> +			if (off > PAGE_SIZE)
> +				link -= class->size / sizeof(*link);
>  			link->next = -1UL << OBJ_TAG_BITS;
>  		}
>  		kunmap_atomic(vaddr);
> -- 
> 2.13.6
>