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

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Message-ID: <20140115143253.GN5698@zion.uk.xensource.com>
Date:	Wed, 15 Jan 2014 14:32:53 +0000
From:	Wei Liu <wei.liu2@...rix.com>
To:	annie li <annie.li@...cle.com>
CC:	David Vrabel <david.vrabel@...rix.com>,
	Wei Liu <wei.liu2@...rix.com>, <xen-devel@...ts.xen.org>,
	<netdev@...r.kernel.org>, <ian.campbell@...rix.com>
Subject: Re: [Xen-devel] [PATCH net-next] xen-netfront: clean up code in
 xennet_release_rx_bufs

On Wed, Jan 15, 2014 at 10:17:08PM +0800, annie li wrote:
[...]
> >Having gnttab_end_foreign_access() do a free just looks odd to me, the
> >free isn't paired with any alloc in the grant table code.
> >
> >It seems more logical to me that granting access takes an additional
> >page ref, and then ending access releases that ref.
> 
> I am thinking of two ways, and they can be implemented in new patches.
> 1. If gnttab_end_foreign_access_ref succeeds, then kfree_skb is
> called to free skb. Otherwise, using gnttab_end_foreign_access to
> release ref and pages.

This is probably not a very good idea as skb_free does a lot more things
than simply freeing pages. You're still leaking something (skb: state,
head etc.) with this approach.

> 2. Add a similar deferred way of gnttab_end_foreign_access in
> gnttab_end_foreign_access_ref.
> 
> Thanks
> Annie
> 
> 
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