netdev - Re: [PATCH] bridge: orphan frags on local receive

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Date:	Mon, 24 Feb 2014 22:31:17 +0800
From:	Qin Chuanyu <qinchuanyu@...wei.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
CC:	<davem@...emloft.net>, KVM list <kvm@...r.kernel.org>,
	<netdev@...r.kernel.org>
Subject: Re: [PATCH] bridge: orphan frags on local receive

On 2014/2/24 21:52, Qin Chuanyu wrote:
> On 2014/2/24 21:29, Michael S. Tsirkin wrote:
>> On Mon, Feb 24, 2014 at 09:12:20PM +0800, Qin Chuanyu wrote:
>>> with vhost tx zero_copy, guest nic might get hang when host reserving
>>> skb in socket queue delivered by guest, the case has been solved in
>>> tun, it also been needed by bridge. This could easily happened when a
>>> LAST_ACK state tcp occuring between guest and host.
>>>
>>> Signed-off-by: Chuanyu Qin <qinchuanyu@...wei.com>
>>
>> Do you actually observe guest hang?
>>
> yes, guest nic could not xmit any more until the skb holded by host has
> been freed, the mainly reason is that though virtio-net could use vring
> desc out of order, but ubufs is been used by vhost in order. so only
> one skb could cause guest nic hang.
>> I would expect orphan frags in
>> __netif_receive_skb_core to be enough.
>>
> yes, it would be better. I would deliver another patch soon.
>>
After thinking for a while, I think that orphan frags could only been
involved in virtual nic receive path, because after
__netif_receive_skb_core, skb would been transmitted by physic nic, in
this way orphan frags is unnecessary.
>>> ---
>>>   net/bridge/br_input.c |    3 +++
>>>   1 files changed, 3 insertions(+), 0 deletions(-)
>>>
>>> diff --git a/net/bridge/br_input.c b/net/bridge/br_input.c
>>> index 28d5446..744e27a 100644
>>> --- a/net/bridge/br_input.c
>>> +++ b/net/bridge/br_input.c
>>> @@ -117,6 +117,8 @@ int br_handle_frame_finish(struct sk_buff *skb)
>>>           br->dev->stats.multicast++;
>>>       } else if ((dst = __br_fdb_get(br, dest, vid)) &&
>>>               dst->is_local) {
>>> +        if (unlikely(skb_orphan_frags(skb, GFP_ATOMIC)))
>>> +            goto drop;
>>>           skb2 = skb;
>>>           /* Do not forward the packet since it's local. */
>>>           skb = NULL;
>>> @@ -136,6 +138,7 @@ int br_handle_frame_finish(struct sk_buff *skb)
>>>   out:
>>>       return 0;
>>>   drop:
>>> +    skb_tx_error(skb);
>>>       kfree_skb(skb);
>>>       goto out;
>>>   }
>>> --
>>> 1.7.3.1.msysgit.0
>>
>>
>
>
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>


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