Subject: Re: [PATCH v3 -next 1/9] DMA, CMA: fix possible memory leak

From: Minchan Kim <[email-masked]>
Date: Mon, 16 Jun 2014 15:27:19 +0900

Hi, Joonsoo

On Mon, Jun 16, 2014 at 02:40:43PM +0900, Joonsoo Kim wrote:
> We should free memory for bitmap when we find zone mis-match,
> otherwise this memory will leak.
> 
> Additionally, I copy code comment from PPC KVM's CMA code to inform
> why we need to check zone mis-match.
> 
> * Note
> Minchan suggested to add a tag for the stable, but, I don't do it,
> because I found this possibility during code-review and, IMO,
> this patch isn't suitable for stable tree.

Nice idea to put the comment in here. Thanks Joonsoo.

It seems you obey "It must fix a real bug that bothers people"
on Documentation/stable_kernel_rules.txt but it's a really obvious
bug and hard to get a report from people because limited user and
hard to detect small such small memory leak.

In my experince, Andrew perfered stable marking for such a obvious
problem but simple fix like this but not sure so let's pass the decision
to him and will learn a lesson from him and will follow the decision
from now on.

Thanks.

Acked-by: Minchan Kim <[email-masked]>

> 
> Acked-by: Zhang Yanfei <[email-masked]>
> Reviewed-by: Michal Nazarewicz <[email-masked]>
> Reviewed-by: Aneesh Kumar K.V <[email-masked]>
> Signed-off-by: Joonsoo Kim <[email-masked]>
> 
> diff --git a/drivers/base/dma-contiguous.c b/drivers/base/dma-contiguous.c
> index 83969f8..6467c91 100644
> --- a/drivers/base/dma-contiguous.c
> +++ b/drivers/base/dma-contiguous.c
> @@ -176,14 +176,24 @@ static int __init cma_activate_area(struct cma *cma)
>  		base_pfn = pfn;
>  		for (j = pageblock_nr_pages; j; --j, pfn++) {
>  			WARN_ON_ONCE(!pfn_valid(pfn));
> +			/*
> +			 * alloc_contig_range requires the pfn range
> +			 * specified to be in the same zone. Make this
> +			 * simple by forcing the entire CMA resv range
> +			 * to be in the same zone.
> +			 */
>  			if (page_zone(pfn_to_page(pfn)) != zone)
> -				return -EINVAL;
> +				goto err;
>  		}
>  		init_cma_reserved_pageblock(pfn_to_page(base_pfn));
>  	} while (--i);
>  
>  	mutex_init(&cma->lock);
>  	return 0;
> +
> +err:
> +	kfree(cma->bitmap);
> +	return -EINVAL;
>  }
>  
>  static struct cma cma_areas[MAX_CMA_AREAS];
> -- 
> 1.7.9.5
> 
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-- 
Kind regards,
Minchan Kim