netdev - Re: [PATCH net] ipv6: make ip6_create_rt_rcu return ip6_null

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Date:   Mon, 18 Mar 2019 20:48:13 +0100
From:   David Ahern <dsa@...ulusnetworks.com>
To:     Xin Long <lucien.xin@...il.com>,
        network dev <netdev@...r.kernel.org>
Cc:     davem@...emloft.net, Wei Wang <weiwan@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>
Subject: Re: [PATCH net] ipv6: make ip6_create_rt_rcu return ip6_null_entry
 instead of NULL

On 3/18/19 12:36 PM, Xin Long wrote:
> diff --git a/net/ipv6/route.c b/net/ipv6/route.c
> index 4ef4bbd..754777d 100644
> --- a/net/ipv6/route.c
> +++ b/net/ipv6/route.c
> @@ -1040,13 +1040,17 @@ static struct rt6_info *ip6_create_rt_rcu(struct fib6_info *rt)
>  	struct rt6_info *nrt;
>  
>  	if (!fib6_info_hold_safe(rt))
> -		return NULL;
> +		goto fallback;
>  
>  	nrt = ip6_dst_alloc(dev_net(dev), dev, flags);
> -	if (nrt)
> +	if (nrt) {
>  		ip6_rt_copy_init(nrt, rt);
> -	else
> +	} else {
>  		fib6_info_release(rt);
> +fallback:
> +		nrt = dev_net(dev)->ipv6.ip6_null_entry;
> +		dst_hold(&nrt->dst);
> +	}
>  
>  	return nrt;
>  }

It seems appropriate for ip6_create_rt_rcu to always return an rt6_info
given its use and v6 design. Since ip6_dst_alloc can also fail (e.g.,
exceed gc_thresh) the fallback case should apply to both.