netdev - RE: [PATCH] net: ip_push_pending

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Date:	Thu, 9 Jul 2009 08:32:33 -0600
From:	"Tantilov, Emil S" <emil.s.tantilov@...el.com>
To:	Eric Dumazet <eric.dumazet@...il.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

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.

Emil
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