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

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Date:	Wed, 15 Jan 2014 11:14:22 +0000
From:	Wei Liu <wei.liu2@...rix.com>
To:	Andrew Bennieston <andrew.bennieston@...rix.com>
CC:	Wei Liu <wei.liu2@...rix.com>, Annie Li <Annie.li@...cle.com>,
	<netdev@...r.kernel.org>, <ian.campbell@...rix.com>,
	<xen-devel@...ts.xen.org>
Subject: Re: [Xen-devel] [PATCH net-next] xen-netfront: clean up code in
 xennet_release_rx_bufs

On Wed, Jan 15, 2014 at 11:02:55AM +0000, Andrew Bennieston wrote:
> On 15/01/14 10:07, Wei Liu wrote:
> >On Fri, Jan 10, 2014 at 06:48:38AM +0800, Annie Li wrote:
> >>Current netfront only grants pages for grant copy, not for grant transfer, so
> >>remove corresponding transfer code and add receiving copy code in
> >>xennet_release_rx_bufs.
> >>
> >
> >This path seldom gets call -- not that many people unload xen-netfront
> >driver. If Annie has tested this patch and it works as expected I think
> >it's fine.
> >
> In XenServer we have seen a number of cases where unplugging and
> replugging VIFs results in leakage of grant references, eventually
> leading to a case where you cannot plug a VIF (after ~ 400 such
> cycles)...
> 

OK, this makes sense.

> It's worth pointing out, as far as this patch is concerned, that
> gnttab_end_foreign_access() can fail, which is not taken into
> account here.
> 

How? gnttab_end_foreign_access doesn't return any error. The gref which
cannot be freed right away will be added to a deferred list and handle
later.

Wei.
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