linux-kernel - Re: [PATCH v2 02/10] DMA, CMA: fix possible memory leak

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Date:	Thu, 12 Jun 2014 16:19:02 +0800
From:	Zhang Yanfei <zhangyanfei@...fujitsu.com>
To:	Joonsoo Kim <iamjoonsoo.kim@....com>
CC:	Minchan Kim <minchan@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Michal Nazarewicz <mina86@...a86.com>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	<kvm@...r.kernel.org>, <linux-mm@...ck.org>,
	Gleb Natapov <gleb@...nel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Alexander Graf <agraf@...e.de>, <kvm-ppc@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, Paul Mackerras <paulus@...ba.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paolo Bonzini <pbonzini@...hat.com>,
	<linuxppc-dev@...ts.ozlabs.org>,
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v2 02/10] DMA, CMA: fix possible memory leak

On 06/12/2014 02:02 PM, Joonsoo Kim wrote:
> On Thu, Jun 12, 2014 at 02:25:43PM +0900, Minchan Kim wrote:
>> On Thu, Jun 12, 2014 at 12:21:39PM +0900, Joonsoo Kim wrote:
>>> We should free memory for bitmap when we find zone mis-match,
>>> otherwise this memory will leak.
>>
>> Then, -stable stuff?
> 
> I don't think so. This is just possible leak candidate, so we don't
> need to push this to stable tree.
> 
>>
>>>
>>> Additionally, I copy code comment from ppc kvm's cma code to notify
>>> why we need to check zone mis-match.
>>>
>>> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>
>>>
>>> diff --git a/drivers/base/dma-contiguous.c b/drivers/base/dma-contiguous.c
>>> index bd0bb81..fb0cdce 100644
>>> --- a/drivers/base/dma-contiguous.c
>>> +++ b/drivers/base/dma-contiguous.c
>>> @@ -177,14 +177,24 @@ 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;
>>
>> At a first glance, I thought it would be better to handle such error
>> before activating.
>> So when I see the registration code(ie, dma_contiguous_revere_area),
>> I realized it is impossible because we didn't set up zone yet. :(
>>
>> If so, when we detect to fail here, it would be better to report more
>> meaningful error message like what was successful zone and what is
>> new zone and failed pfn number?
> 
> What I want to do in early phase of this patchset is to make cma code
> on DMA APIs similar to ppc kvm's cma code. ppc kvm's cma code already
> has this error handling logic, so I make this patch.
> 
> If we think that we need more things, we can do that on general cma code
> after merging this patchset.
> 

Yeah, I also like the idea. After all, this patchset aims to a general CMA
management, we could improve more after this patchset. So

Acked-by: Zhang Yanfei <zhangyanfei@...fujitsu.com>

-- 
Thanks.
Zhang Yanfei
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