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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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