netdev - Re: [PATCH] route:ip_rt_frag_needed always return unzero

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Date:	Wed, 19 Oct 2011 13:20:28 +0800
From:	Gao feng <gaofeng@...fujitsu.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	davem@...emloft.net, kuznet@....inr.ac.ru, jmorris@...ei.org,
	netdev@...r.kernel.org
Subject: Re: [PATCH] route:ip_rt_frag_needed always return unzero

于 2011年10月19日 11:49, Eric Dumazet 写道:
> Le mercredi 19 octobre 2011 à 09:34 +0800, Gao feng a écrit :
>> 2011.10.18 17:23, Eric Dumazet wrote:
>>> Le mardi 18 octobre 2011 à 15:04 +0800, Gao feng a écrit :
>>>> int function ip_rt_frag_need,if peer is null,
>>>> there is no need to do ipprot->err_handler.
>>>> I am right?
>>>>
>>>> Signed-off-by: Gao feng <gaofeng@...fujitsu.com>
>>>> ---
>>>>  net/ipv4/route.c |    2 +-
>>>>  1 files changed, 1 insertions(+), 1 deletions(-)
>>>>
>>>> diff --git a/net/ipv4/route.c b/net/ipv4/route.c
>>>> index 075212e..6cde0fa 100644
>>>> --- a/net/ipv4/route.c
>>>> +++ b/net/ipv4/route.c
>>>> @@ -1574,7 +1574,7 @@ unsigned short ip_rt_frag_needed(struct net *net, const struct iphdr *iph,
>>>>  
>>>>  		atomic_inc(&__rt_peer_genid);
>>>>  	}
>>>> -	return est_mtu ? : new_mtu;
>>>> +	return est_mtu;
>>>>  }
>>>>  
>>>>  static void check_peer_pmtu(struct dst_entry *dst, struct inet_peer *peer)
>>>
>>> No idea why you want this, your changelog is a bit cryptic :)
>>>
>>> Wont this bypass the raw_icmp_error(skb, protocol, info);
>>> call in icmp_unreach() as well ?
>>>
>>>
>>
>> thanks Eric!
>>
>> I mean that the pmtu is update by inet_peer->pmtu_learned as I know.
>> so in function ip_rt_frag_needed,
>> if inet_peer is null or someting else make the setting of inet_peer->pmtu_learned failed.
>> there is no need to call function tcp_v4_err.
>>
>> the call stack is
>> icmp_unreach
>>   |
>>   |--->ip_rt_frag_needed(fill inet_peer)
>>   |
>>   |--->raw_icmp_error()
>>   |
>>   |--->ipprot->err_handler(tcp_v4_err or something else)
>> 	|
>> 	|--->tcp_v4_err(frag need icmp is triggered by tcp packet)
>> 		|
>> 		|--->do_pmtu_discovery
>> 		(in this function both __sk_dst_check or dst->ops->update_pmtu
>> 		need struct inet_peer to update pmtu)
>>
>> so,I think when set inet_peer->pmtu_learned failed,
>> in func icmp_unreach we should goto out immediately.
>>
>> And it's confuse me that why func ping_err and udp_err not update the pmtu?
>> What I miss?
> 
> You dont answer my question : After your patch, we now dont call
> raw_icmp_error() anymore. Why is is valid ?

After my patch
raw_icmp_error don't call only when setting inet_peer failed(ip_rt_frag_needed return zero).
And I think it's unexpected,should goto out immediately.

In orig ip_rt_frag_need,
zero can be return only when pmtu(get from icmp packet) is zero and peer is NULL.
in this case,raw_icmp_error will not be call too.this is valid??

The return value of ip_rt_frag_needed is not very clear.
Eric,can you tell me something?

> 
> Not finding/create inet_peer is very unlikely : This occurs only under
> high stress and out of memory condition. Is it really happening on your
> machines ?
> 
> 

It's not happening on my machines.

thanks.

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