netdev - Re: [PATCH] net: ip_push_pending

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Date:	Thu, 09 Jul 2009 16:38:52 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	"Tantilov, Emil S" <emil.s.tantilov@...el.com>
CC:	David Miller <davem@...emloft.net>,
	"emils.tantilov@...il.com" <emils.tantilov@...il.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"Brandeburg, Jesse" <jesse.brandeburg@...el.com>,
	"Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>,
	"jolsa@...hat.com" <jolsa@...hat.com>
Subject: Re: [PATCH] net: ip_push_pending_frames() fix

Tantilov, Emil S a écrit :
> Eric Dumazet wrote:
>> Tantilov, Emil S a écrit :
>>> Eric Dumazet wrote:
>>>> David Miller a écrit :
>>>>> From: "Tantilov, Emil S" <emil.s.tantilov@...el.com>
>>>>> Date: Wed, 8 Jul 2009 11:02:22 -0600
>>>>>
>>>>>> Still seeing traces during the test even with this patch applied:
>>>>>>
>>>>>> [ 1089.430093] ------------[ cut here ]------------
>>>>>> [ 1089.435667] WARNING: at include/net/sock.h:423
>>>>>> udp_lib_unhash+0x73/0xa0() [ 1089.435670] Hardware name: S5520HC
>>>>> Ok I'll back this out for now, needs more investigation
>>>>> obviously.
>>>> Hmm... I never said it was supposed to fix Emil problem, just that
>>>> I discovered one potential problem by code inspection.
>>>>
>>>> I could not find yet sk_refcnt mismatch.
>>>> As we do less atomic ops per packet than before, some old bug could
>>>> surface now... 
>>>>
>>>> Emil, is it easy to reproduce this problem, considering I have a
>>>> similar platform than yours (dual quad core machine, E5450 cpus @
>>>> 3GHz) ?
>>> Eric,
>>>
>>> It should be easy to reproduce. At least I have been able to
>>> consistently 
>>> reproduce it on several different systems with different drivers
>>> (e1000, e1000e, igb). 
>>>
>>> The test I'm running is a mix of IPV4/6 TCP/UDP traffic with netperf
>>> (also mixing different types TCP/UDP_STREAM, TCP_MAERTS, TCP_UDP_RR
>>> etc). How much this matters I don't know - it's possible that just
>>> UDP traffic would do it. I also think it may have something to do
>>> with IPv6 because of the trace, but I am not sure.   
>>>
>>> If you need more information let me know.
>>>
>> OK thanks, this was helpful, corking or not corking, that is the
>> question :) 
>>
>> I think ip6_push_pending_frames() & ip_push_pending_frames
>> have a problem after recent commit
>> 2b85a34e911bf483c27cfdd124aeb1605145dc80 (net: No more expensive
>> sock_hold()/sock_put() on each tx) 
>>
>> [PATCH] net: ip_push_pending_frames() fix
>>
>> After commit 2b85a34e911bf483c27cfdd124aeb1605145dc80
>> (net: No more expensive sock_hold()/sock_put() on each tx)
>> we do not take any more references on sk->sk_refcnt on outgoing
>> packets. 
>>
>> I forgot to delete two __sock_put() from ip_push_pending_frames()
>> and ip6_push_pending_frames().
>>
>> Reported-by: Emil S Tantilov <emils.tantilov@...il.com>
>> Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
>> ---
>> diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
>> index 2470262..7d08210 100644
>> --- a/net/ipv4/ip_output.c
>> +++ b/net/ipv4/ip_output.c
>> @@ -1243,7 +1243,6 @@ int ip_push_pending_frames(struct sock *sk)
>>  		skb->len += tmp_skb->len;
>>  		skb->data_len += tmp_skb->len;
>>  		skb->truesize += tmp_skb->truesize;
>> -		__sock_put(tmp_skb->sk);
>>  		tmp_skb->destructor = NULL;
>>  		tmp_skb->sk = NULL;
>>  	}
>> diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
>> index 7c76e3d..87f8419 100644
>> --- a/net/ipv6/ip6_output.c
>> +++ b/net/ipv6/ip6_output.c
>> @@ -1484,7 +1484,6 @@ int ip6_push_pending_frames(struct sock *sk)
>>  		skb->len += tmp_skb->len;
>>  		skb->data_len += tmp_skb->len;
>>  		skb->truesize += tmp_skb->truesize;
>> -		__sock_put(tmp_skb->sk);
>>  		tmp_skb->destructor = NULL;
>>  		tmp_skb->sk = NULL;
>>  	}
> 
> Thanks Eric,
> 
> With this patch the test ran all night without issues.
> 

Thanks a lot Emil for testing and your feedback.

David, could you please add another tag ?

Tested-by: Emil S Tantilov <emils.tantilov@...il.com>

Thanks
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