netdev - Re: [RFT Patch net 1/2] ipv6: invalidate the socket cached route on pmtu events if possible

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Date:	Thu, 24 Mar 2016 13:35:40 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Cong Wang <xiyou.wangcong@...il.com>
Cc:	netdev@...r.kernel.org, weiwan@...gle.com,
	Steffen Klassert <steffen.klassert@...unet.com>,
	Martin KaFai Lau <kafai@...com>,
	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	Julian Anastasov <ja@....bg>
Subject: Re: [RFT Patch net 1/2] ipv6: invalidate the socket cached route on
 pmtu events if possible

On Thu, 2016-03-24 at 12:25 -0700, Cong Wang wrote:

>  void ip6_sk_update_pmtu(struct sk_buff *skb, struct sock *sk, __be32 mtu)
>  {
> -	ip6_update_pmtu(skb, sock_net(sk), mtu,
> -			sk->sk_bound_dev_if, sk->sk_mark);
> +	const struct ipv6hdr *iph = (struct ipv6hdr *)skb->data;
> +	struct net *net = sock_net(sk);
> +	struct dst_entry *ndst, *dst;
> +	struct flowi6 fl6;
> +	bool new = false;
> +
> +	memset(&fl6, 0, sizeof(fl6));
> +
> +	bh_lock_sock(sk);
> +


This is not clear why you need to acquire socket lock.

sk_dst_cache is protected by an atomic operation.

udp for example calls ip6_dst_store() without socket being locked.