linux-kernel - Re: [PATCH] zsmalloc: fix linking bug in init

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Message-ID: <20180813060549.GB64836@rodete-desktop-imager.corp.google.com>
Date:   Mon, 13 Aug 2018 15:05:49 +0900
From:   Minchan Kim <minchan@...nel.org>
To:     zhouxianrong <zhouxianrong@....com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        ngupta@...are.org, sergey.senozhatsky.work@...il.com,
        zhouxianrong <zhouxianrong@...wei.com>
Subject: Re: [PATCH] zsmalloc: fix linking bug in init_zspage

Hi,

On Thu, Aug 09, 2018 at 08:28:17PM -0400, zhouxianrong wrote:
> From: zhouxianrong <zhouxianrong@...wei.com>
> 
> 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@...wei.com>
> ---
>  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
>