Re: [PATCH v2 3/7] mm/compaction: correctly return failure with bogus compound_order in strict mode

[Baolin Wang <baolin.wang@linux.alibaba.com>]

On 8/26/2023 11:36 PM, Kemeng Shi wrote:
> In strict mode, we should return 0 if there is any hole in pageblock. If
> we successfully isolated pages at beginning at pageblock and then have a
> bogus compound_order outside pageblock in next page. We will abort search
> loop with blockpfn > end_pfn. Although we will limit blockpfn to end_pfn,
> we will treat it as a successful isolation in strict mode as blockpfn is
> not < end_pfn and return partial isolated pages. Then
> isolate_freepages_range may success unexpectly with hole in isolated
> range.
> 
> Fixes: 9fcd6d2e052ee ("mm, compaction: skip compound pages by order in free scanner")
> Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>

LGTM.
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>

> ---
>   mm/compaction.c | 11 +++++++++--
>   1 file changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/compaction.c b/mm/compaction.c
> index a40550a33aee..b4d03c9ffe7c 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -631,6 +631,14 @@ static unsigned long isolate_freepages_block(struct compact_control *cc,
>   				page += (1UL << order) - 1;
>   				nr_scanned += (1UL << order) - 1;
>   			}
> +			/*
> +			 * There is a tiny chance that we have read bogus
> +			 * compound_order(), so be careful to not go outside
> +			 * of the pageblock.
> +			 */
> +			if (unlikely(blockpfn >= end_pfn))
> +				blockpfn = end_pfn - 1;
> +
>   			goto isolate_fail;
>   		}
>   
> @@ -678,8 +686,7 @@ static unsigned long isolate_freepages_block(struct compact_control *cc,
>   		spin_unlock_irqrestore(&cc->zone->lock, flags);
>   
>   	/*
> -	 * There is a tiny chance that we have read bogus compound_order(),
> -	 * so be careful to not go outside of the pageblock.
> +	 * Be careful to not go outside of the pageblock.
>   	 */
>   	if (unlikely(blockpfn > end_pfn))
>   		blockpfn = end_pfn;