linux-kernel - Re: [PATCH v2] core, nfqueue, openvswitch: Orphan frags in skb

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Message-ID: <532B10F7.60801@citrix.com>
Date:	Thu, 20 Mar 2014 16:01:59 +0000
From:	Zoltan Kiss <zoltan.kiss@...rix.com>
To:	Thomas Graf <tgraf@...hat.com>, Jesse Gross <jesse@...ira.com>,
	<pshelar@...ira.com>, <dev@...nvswitch.org>
CC:	"David S. Miller" <davem@...emloft.net>,
	Pablo Neira Ayuso <pablo@...filter.org>,
	Jozsef Kadlecsik <kadlec@...ckhole.kfki.hu>,
	Eric Dumazet <edumazet@...gle.com>,
	Daniel Borkmann <dborkman@...hat.com>,
	Tom Herbert <therbert@...gle.com>,
	Jason Wang <jasowang@...hat.com>,
	Florian Westphal <fw@...len.de>, Joe Perches <joe@...ches.com>,
	Simon Horman <horms@...ge.net.au>,
	Jiri Pirko <jiri@...nulli.us>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Paul Durrant <Paul.Durrant@...rix.com>,
	Jan Beulich <JBeulich@...e.com>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Miklos Szeredi <mszeredi@...e.cz>,
	<netfilter-devel@...r.kernel.org>, <netfilter@...r.kernel.org>,
	<xen-devel@...ts.xenproject.org>, <netdev@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <kvm@...r.kernel.org>
Subject: Re: [PATCH v2] core, nfqueue, openvswitch: Orphan frags in skb_zerocopy
 and handle errors

On 20/03/14 12:33, Thomas Graf wrote:
> On 03/20/2014 01:16 PM, Thomas Graf wrote:
>> On 03/19/2014 10:07 PM, Zoltan Kiss wrote:
>>> skb_zerocopy can copy elements of the frags array between skbs, but it
>>> doesn't
>>> orphan them. Also, it doesn't handle errors, so this patch takes care
>>> of that
>>> as well.
>>>
>>> Signed-off-by: Zoltan Kiss <zoltan.kiss@...rix.com>
>>
>> Acked-by: Thomas Graf <tgraf@...hat.com>
>
> I take this back ;)
>
>>> ---
>>> +    if (unlikely(skb_orphan_frags(to, GFP_ATOMIC))) {
>>> +        skb_tx_error(to);
>>> +        return -ENOMEM;
>>> +    }
>
> Just noticed that you orphan the Netlink skb frags which do not
> exist yet instead of the source skb frags.
Oh, sorry, I'll fix this up.

>
>> Did you consider calling skb_tx_error() for Netlink message
>> allocation failures for the upcall as well? That memory pressure
>> is currently not reported back.
Yeah, that makes sense, I'll fix it the callers. Btw. I guess that just 
provides some statistical data for the creator of the skb. At least for 
netback it only increment a stat counter.

Zoli


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