netdev - Re: [PATCH 1/1] Use RCU for the UDP hash lock

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Message-id: <48DBE327.8010709@acm.org>
Date:	Thu, 25 Sep 2008 14:14:47 -0500
From:	Corey Minyard <minyard@....org>
To:	Jarek Poplawski <jarkao2@...il.com>
Cc:	Linux Kernel <linux-kernel@...r.kernel.org>, netdev@...r.kernel.org
Subject: Re: [PATCH 1/1] Use RCU for the UDP hash lock

Jarek Poplawski wrote:
>
> ...
>   
>> @@ -1094,7 +1103,7 @@ static int __udp4_lib_mcast_deliver(struct net *net, struct sk_buff *skb,
>>  	struct sock *sk;
>>  	int dif;
>>  
>> -	read_lock(&udp_hash_lock);
>> +	rcu_read_lock();
>>  	sk = sk_head(&udptable[udp_hashfn(net, ntohs(uh->dest))]);
>>     
>
> Probably sk_head_rcu() is needed too.
>   
Yes, it is.
>   
>>  	dif = skb->dev->ifindex;
>>  	sk = udp_v4_mcast_next(sk, uh->dest, daddr, uh->source, saddr, dif);
>> @@ -1120,7 +1129,7 @@ static int __udp4_lib_mcast_deliver(struct net *net, struct sk_buff *skb,
>>  		} while (sknext);
>>  	} else
>>  		kfree_skb(skb);
>> -	read_unlock(&udp_hash_lock);
>> +	rcu_read_unlock();
>>  	return 0;
>>  }
>>     
> ...
>
> Aren't other functions like sk_next() or sk_unhashed() used on the
> read side and need _rcu versions?
>   
It also needs sk_next_rcu().  sk_unhashed() is only used on the update 
side, so an rcu version is not needed there.

Thanks for pointing this out.

-corey

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