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

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Date:	Mon, 24 Feb 2014 21:52:11 +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 21:29, 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.
>
>> ---
>>   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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