ipv6: replace write lock with read lock when get route info

geting route info does not write rt->rt6i_table, so replace
write lock with read lock
Suggested-by: NEric Dumazet <edumazet@google.com>
Signed-off-by: NLi RongQing <roy.qing.li@gmail.com>
Signed-off-by: NEric Dumazet <edumazet@google.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv6/addrconf.c

@@ -1708,7 +1708,7 @@ static struct rt6_info *addrconf_get_prefix_route(const struct in6_addr *pfx,
 	if (table == NULL)
 		return NULL;
 
-	write_lock_bh(&table->tb6_lock);
+	read_lock_bh(&table->tb6_lock);
 	fn = fib6_locate(&table->tb6_root, pfx, plen, NULL, 0);
 	if (!fn)
 		goto out;
@@ -1723,7 +1723,7 @@ static struct rt6_info *addrconf_get_prefix_route(const struct in6_addr *pfx,
 		break;
 	}
 out:
-	write_unlock_bh(&table->tb6_lock);
+	read_unlock_bh(&table->tb6_lock);
 	return rt;
 }
 

net/ipv6/route.c

@@ -1837,7 +1837,7 @@ static struct rt6_info *rt6_get_route_info(struct net *net,
 	if (!table)
 		return NULL;
 
-	write_lock_bh(&table->tb6_lock);
+	read_lock_bh(&table->tb6_lock);
 	fn = fib6_locate(&table->tb6_root, prefix ,prefixlen, NULL, 0);
 	if (!fn)
 		goto out;
@@ -1853,7 +1853,7 @@ static struct rt6_info *rt6_get_route_info(struct net *net,
 		break;
 	}
 out:
-	write_unlock_bh(&table->tb6_lock);
+	read_unlock_bh(&table->tb6_lock);
 	return rt;
 }
 
@@ -1896,7 +1896,7 @@ struct rt6_info *rt6_get_dflt_router(const struct in6_addr *addr, struct net_dev
 	if (!table)
 		return NULL;
 
-	write_lock_bh(&table->tb6_lock);
+	read_lock_bh(&table->tb6_lock);
 	for (rt = table->tb6_root.leaf; rt; rt=rt->dst.rt6_next) {
 		if (dev == rt->dst.dev &&
 		    ((rt->rt6i_flags & (RTF_ADDRCONF | RTF_DEFAULT)) == (RTF_ADDRCONF | RTF_DEFAULT)) &&
@@ -1905,7 +1905,7 @@ struct rt6_info *rt6_get_dflt_router(const struct in6_addr *addr, struct net_dev
 	}
 	if (rt)
 		dst_hold(&rt->dst);
-	write_unlock_bh(&table->tb6_lock);
+	read_unlock_bh(&table->tb6_lock);
 	return rt;
 }