ipv6: Avoid double dst_free
It is a prep work to get dst freeing from fib tree undergo
a rcu grace period.
The following is a common paradigm:
if (ip6_del_rt(rt))
dst_free(rt)
which means, if rt cannot be deleted from the fib tree, dst_free(rt) now.
1. We don't know the ip6_del_rt(rt) failure is because it
was not managed by fib tree (e.g. DST_NOCACHE) or it had already been
removed from the fib tree.
2. If rt had been managed by the fib tree, ip6_del_rt(rt) failure means
dst_free(rt) has been called already. A second
dst_free(rt) is not always obviously safe. The rt may have
been destroyed already.
3. If rt is a DST_NOCACHE, dst_free(rt) should not be called.
4. It is a stopper to make dst freeing from fib tree undergo a
rcu grace period.
This patch is to use a DST_NOCACHE flag to indicate a rt is
not managed by the fib tree.
Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 53617d7..3d3c1b2 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -1322,8 +1322,7 @@
if (rt) {
if (rt->rt6i_flags & RTF_CACHE) {
dst_hold(&rt->dst);
- if (ip6_del_rt(rt))
- dst_free(&rt->dst);
+ ip6_del_rt(rt);
} else if (rt->rt6i_node && (rt->rt6i_flags & RTF_DEFAULT)) {
rt->rt6i_node->fn_sernum = -1;
}
@@ -2028,7 +2027,8 @@
struct fib6_table *table;
struct net *net = dev_net(rt->dst.dev);
- if (rt == net->ipv6.ip6_null_entry) {
+ if (rt == net->ipv6.ip6_null_entry ||
+ rt->dst.flags & DST_NOCACHE) {
err = -ENOENT;
goto out;
}
@@ -2515,6 +2515,7 @@
rt->rt6i_dst.addr = *addr;
rt->rt6i_dst.plen = 128;
rt->rt6i_table = fib6_get_table(net, RT6_TABLE_LOCAL);
+ rt->dst.flags |= DST_NOCACHE;
atomic_set(&rt->dst.__refcnt, 1);