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ipv6: Avoid double dst_free

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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>
This commit is contained in:
Martin KaFai Lau 2015-09-15 14:30:08 -07:00 committed by David S. Miller
parent cdf3464e6c
commit 8e3d5be736
3 changed files with 16 additions and 9 deletions
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7
net/ipv6/addrconf.c
View File

@ -5127,13 +5127,12 @@ static void __ipv6_ifa_notify(int event, struct inet6_ifaddr *ifp)
rt = addrconf_get_prefix_route(&ifp->peer_addr, 128,
ifp->idev->dev, 0, 0);
if (rt && ip6_del_rt(rt))
dst_free(&rt->dst);
if (rt)
ip6_del_rt(rt);
}
dst_hold(&ifp->rt->dst);
if (ip6_del_rt(ifp->rt))
dst_free(&ifp->rt->dst);
ip6_del_rt(ifp->rt);
rt_genid_bump_ipv6(net);
break;

11
net/ipv6/ip6_fib.c
View File

@ -933,6 +933,10 @@ int fib6_add(struct fib6_node *root, struct rt6_info *rt,
int replace_required = 0;
int sernum = fib6_new_sernum(info->nl_net);
if (WARN_ON_ONCE((rt->dst.flags & DST_NOCACHE) &&
!atomic_read(&rt->dst.__refcnt)))
return -EINVAL;
if (info->nlh) {
if (!(info->nlh->nlmsg_flags & NLM_F_CREATE))
allow_create = 0;
@ -1025,6 +1029,7 @@ int fib6_add(struct fib6_node *root, struct rt6_info *rt,
fib6_start_gc(info->nl_net, rt);
if (!(rt->rt6i_flags & RTF_CACHE))
fib6_prune_clones(info->nl_net, pn);
rt->dst.flags &= ~DST_NOCACHE;
}
out:
@ -1049,7 +1054,8 @@ out:
atomic_inc(&pn->leaf->rt6i_ref);
}
#endif
dst_free(&rt->dst);
if (!(rt->dst.flags & DST_NOCACHE))
dst_free(&rt->dst);
}
return err;
@ -1060,7 +1066,8 @@ out:
st_failure:
if (fn && !(fn->fn_flags & (RTN_RTINFO|RTN_ROOT)))
fib6_repair_tree(info->nl_net, fn);
dst_free(&rt->dst);
if (!(rt->dst.flags & DST_NOCACHE))
dst_free(&rt->dst);
return err;
#endif
}

7
net/ipv6/route.c
View File

@ -1322,8 +1322,7 @@ static void ip6_link_failure(struct sk_buff *skb)
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 @@ static int __ip6_del_rt(struct rt6_info *rt, struct nl_info *info)
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 @@ struct rt6_info *addrconf_dst_alloc(struct inet6_dev *idev,
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);