netdev - Re: [Xen-devel][PATCH net-next v2] xen-netfront: clean up code in xennet_release_rx

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Date:	Thu, 16 Jan 2014 21:42:19 +0800
From:	annie li <annie.li@...cle.com>
To:	David Vrabel <david.vrabel@...rix.com>
CC:	xen-devel@...ts.xen.org, netdev@...r.kernel.org,
	davem@...emloft.net, konrad.wilk@...cle.com,
	ian.campbell@...rix.com, wei.liu2@...rix.com,
	andrew.bennieston@...rix.com
Subject: Re: [Xen-devel][PATCH net-next v2] xen-netfront: clean up code in
 xennet_release_rx_bufs


On 2014-1-16 19:10, David Vrabel wrote:
> On 15/01/14 23:57, Annie Li wrote:
>> This patch implements two things:
>>
>> * release grant reference and skb for rx path, this fixex resource leaking.
>> * clean up grant transfer code kept from old netfront(2.6.18) which grants
>> pages for access/map and transfer. But grant transfer is deprecated in current
>> netfront, so remove corresponding release code for transfer.
>>
>> gnttab_end_foreign_access_ref may fail when the grant entry is currently used
>> for reading or writing. But this patch does not cover this and improvement for
>> this failure may be implemented in a separate patch.
> I don't think replacing a resource leak with a security bug is a good idea.
>
> If you would prefer not to fix the gnttab_end_foreign_access() call, I
> think you can fix this in netfront by taking a reference to the page
> before calling gnttab_end_foreign_access().  This will ensure the page
> isn't freed until the subsequent kfree_skb(), or the gref is released by
> the foreign domain (whichever is later).

What I thought is to split the implementation into two patches, this 
patch fixes the rx path resource leak(just like what tx path does), then 
a separate patch fixes gnttab_end_foreign_access_ref failure issue for 
both tx/rx through taking reference to the page before 
gnttab_end_foreign_access.
If you'd like they are posted together, I will create new patch for the 
latter and then post them.:-)

Thanks
Annie
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