netdev - Re: [PATCH net-next v2 1/3] net: ipv6: Allow shorthand delete of all nexthops in multipath route

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Message-Id: <20170116.195139.2265183195514595519.davem@davemloft.net>
Date:   Mon, 16 Jan 2017 19:51:39 -0500 (EST)
From:   David Miller <davem@...emloft.net>
To:     dsa@...ulusnetworks.com
Cc:     netdev@...r.kernel.org, ddutt@...ulusnetworks.com
Subject: Re: [PATCH net-next v2 1/3] net: ipv6: Allow shorthand delete of
 all nexthops in multipath route

From: David Ahern <dsa@...ulusnetworks.com>
Date: Sun, 15 Jan 2017 12:07:04 -0800

> @@ -2143,6 +2143,26 @@ int ip6_del_rt(struct rt6_info *rt)
>  	return __ip6_del_rt(rt, &info);
>  }
>  
> +/* called with table lock held */
 ...
> @@ -2176,10 +2196,9 @@ static int ip6_route_del(struct fib6_config *cfg)
>  				continue;
>  			if (cfg->fc_protocol && cfg->fc_protocol != rt->rt6i_protocol)
>  				continue;
> -			dst_hold(&rt->dst);
> -			read_unlock_bh(&table->tb6_lock);
>  
> -			return __ip6_del_rt(rt, &cfg->fc_nlinfo);
> +			err = __ip6_route_del(rt, cfg);
> +			break;
>  		}

fib6_del() (invoked by __ip6_route_del()) has to be invoked with the
table lock held a sa writer, but here you are only holding it as a
reader.

I also think some more thought has to be put into whether we can
change behavior like this without using a flag, as suggested by Roopa.