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Date: Thu, 11 Sep 2014 10:44:04 -0400
From: Vlad Yasevich <vyasevich@...il.com>
To: Hannes Frederic Sowa <hannes@...essinduktion.org>
CC: David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
eric.dumazet@...il.com, nicolas.dichtel@...nd.com
Subject: Re: [PATCH net-next] ipv6: implement rt_genid_bump_ipv6 with fn_sernum
and remove rt6i_genid
On 09/11/2014 10:32 AM, Hannes Frederic Sowa wrote:
> On Do, 2014-09-11 at 10:19 -0400, Vlad Yasevich wrote:
>> On 09/11/2014 08:05 AM, Hannes Frederic Sowa wrote:
>>> On Mi, 2014-09-10 at 13:09 -0700, David Miller wrote:
>>>> From: Hannes Frederic Sowa <hannes@...essinduktion.org>
>>>> Date: Wed, 10 Sep 2014 11:31:28 +0200
>>>>
>>>>> In case we need to force the sockets to relookup the routes we now
>>>>> increase the fn_sernum on all fibnodes in the routing tree. This is a
>>>>> costly operation but should only happen if we have major routing/policy
>>>>> changes in the kernel (e.g. manual route adding/removal, xfrm policy
>>>>> changes).
>>>>
>>>> Core routers can update thousands of route updates per second, and they
>>>> do this via what you refer to as "manual route adding/removal".
>>>>
>>>> I don't think we want to put such a scalability problem into the tree.
>>>>
>>>> There has to be a lightweight way to address this.
>>>
>>> An alternative approach without traversing the routing table, but each
>>> newly inserted route (even only cached ones) might bump all other routes
>>> out of the per-socket caches:
>>>
>>> diff --git a/include/net/ip6_fib.h b/include/net/ip6_fib.h
>>> index 9bcb220..a7e45b9 100644
>>> --- a/include/net/ip6_fib.h
>>> +++ b/include/net/ip6_fib.h
>>> @@ -119,8 +119,6 @@ struct rt6_info {
>>> struct inet6_dev *rt6i_idev;
>>> unsigned long _rt6i_peer;
>>>
>>> - u32 rt6i_genid;
>>> -
>>> /* more non-fragment space at head required */
>>> unsigned short rt6i_nfheader_len;
>>>
>>> diff --git a/include/net/net_namespace.h b/include/net/net_namespace.h
>>> index 361d260..428fdcb 100644
>>> --- a/include/net/net_namespace.h
>>> +++ b/include/net/net_namespace.h
>>> @@ -358,18 +358,28 @@ static inline int rt_genid_ipv6(struct net *net)
>>> return atomic_read(&net->ipv6.rt_genid);
>>> }
>>>
>>> -static inline void rt_genid_bump_ipv6(struct net *net)
>>> +static inline int rt_genid_bump_ipv6(struct net *net)
>>> {
>>> - atomic_inc(&net->ipv6.rt_genid);
>>> + int new, old;
>>> +
>>> + do {
>>> + old = atomic_read(&net->ipv6.rt_genid);
>>> + new = old + 1;
>>> + if (new <= 0)
>>> + new = 1;
>>> + } while (atomic_cmpxchg(&net->ipv6.rt_genid, old, new) != old);
>>> + return new;
>>> +
>>> }
>>> #else
>>> static inline int rt_genid_ipv6(struct net *net)
>>> {
>>> - return 0;
>>> + return 1;
>>> }
>>>
>>> -static inline void rt_genid_bump_ipv6(struct net *net)
>>> +static inline int rt_genid_bump_ipv6(struct net *net)
>>> {
>>> + return 1;
>>> }
>>> #endif
>>>
>>> diff --git a/net/ipv6/ip6_fib.c b/net/ipv6/ip6_fib.c
>>> index 76b7f5e..4a2f130 100644
>>> --- a/net/ipv6/ip6_fib.c
>>> +++ b/net/ipv6/ip6_fib.c
>>> @@ -84,7 +84,10 @@ static int fib6_walk_continue(struct fib6_walker_t *w);
>>> * result of redirects, path MTU changes, etc.
>>> */
>>>
>>> -static __u32 rt_sernum;
>>> +static int fib6_new_sernum(struct net *net)
>>> +{
>>> + return rt_genid_bump_ipv6(net);
>>> +}
>>>
>>> static void fib6_gc_timer_cb(unsigned long arg);
>>>
>>> @@ -104,13 +107,6 @@ static inline void fib6_walker_unlink(struct fib6_walker_t *w)
>>> list_del(&w->lh);
>>> write_unlock_bh(&fib6_walker_lock);
>>> }
>>> -static __inline__ u32 fib6_new_sernum(void)
>>> -{
>>> - u32 n = ++rt_sernum;
>>> - if ((__s32)n <= 0)
>>> - rt_sernum = n = 1;
>>> - return n;
>>> -}
>>>
>>> /*
>>> * Auxiliary address test functions for the radix tree.
>>> @@ -421,16 +417,15 @@ out:
>>> */
>>>
>>> static struct fib6_node *fib6_add_1(struct fib6_node *root,
>>> - struct in6_addr *addr, int plen,
>>> - int offset, int allow_create,
>>> - int replace_required)
>>> + struct in6_addr *addr, int plen,
>>> + int offset, int allow_create,
>>> + int replace_required, int sernum)
>>> {
>>> struct fib6_node *fn, *in, *ln;
>>> struct fib6_node *pn = NULL;
>>> struct rt6key *key;
>>> int bit;
>>> __be32 dir = 0;
>>> - __u32 sernum = fib6_new_sernum();
>>>
>>> RT6_TRACE("fib6_add_1\n");
>>>
>>> @@ -844,6 +839,7 @@ void fib6_force_start_gc(struct net *net)
>>> int fib6_add(struct fib6_node *root, struct rt6_info *rt, struct nl_info *info,
>>> struct nlattr *mx, int mx_len)
>>> {
>>> + struct net *net = dev_net(rt->dst.dev);
>>> struct fib6_node *fn, *pn = NULL;
>>> int err = -ENOMEM;
>>> int allow_create = 1;
>>> @@ -860,7 +856,7 @@ int fib6_add(struct fib6_node *root, struct rt6_info *rt, struct nl_info *info,
>>>
>>> fn = fib6_add_1(root, &rt->rt6i_dst.addr, rt->rt6i_dst.plen,
>>> offsetof(struct rt6_info, rt6i_dst), allow_create,
>>> - replace_required);
>>> + replace_required, fib6_new_sernum(net));
>>> if (IS_ERR(fn)) {
>>> err = PTR_ERR(fn);
>>> fn = NULL;
>>> @@ -894,14 +890,15 @@ int fib6_add(struct fib6_node *root, struct rt6_info *rt, struct nl_info *info,
>>> sfn->leaf = info->nl_net->ipv6.ip6_null_entry;
>>> atomic_inc(&info->nl_net->ipv6.ip6_null_entry->rt6i_ref);
>>> sfn->fn_flags = RTN_ROOT;
>>> - sfn->fn_sernum = fib6_new_sernum();
>>> + sfn->fn_sernum = fib6_new_sernum(net);
>>>
>>> /* Now add the first leaf node to new subtree */
>>>
>>> sn = fib6_add_1(sfn, &rt->rt6i_src.addr,
>>> rt->rt6i_src.plen,
>>> offsetof(struct rt6_info, rt6i_src),
>>> - allow_create, replace_required);
>>> + allow_create, replace_required,
>>> + fib6_new_sernum(net));
>>>
>>> if (IS_ERR(sn)) {
>>> /* If it is failed, discard just allocated
>>> @@ -920,7 +917,8 @@ int fib6_add(struct fib6_node *root, struct rt6_info *rt, struct nl_info *info,
>>> sn = fib6_add_1(fn->subtree, &rt->rt6i_src.addr,
>>> rt->rt6i_src.plen,
>>> offsetof(struct rt6_info, rt6i_src),
>>> - allow_create, replace_required);
>>> + allow_create, replace_required,
>>> + fib6_new_sernum(net));
>>>
>>> if (IS_ERR(sn)) {
>>> err = PTR_ERR(sn);
>>> diff --git a/net/ipv6/route.c b/net/ipv6/route.c
>>> index f74b041..54b7d81 100644
>>> --- a/net/ipv6/route.c
>>> +++ b/net/ipv6/route.c
>>> @@ -314,7 +314,6 @@ static inline struct rt6_info *ip6_dst_alloc(struct net *net,
>>>
>>> memset(dst + 1, 0, sizeof(*rt) - sizeof(*dst));
>>> rt6_init_peer(rt, table ? &table->tb6_peers : net->ipv6.peers);
>>> - rt->rt6i_genid = rt_genid_ipv6(net);
>>> INIT_LIST_HEAD(&rt->rt6i_siblings);
>>> }
>>> return rt;
>>> @@ -1096,10 +1095,7 @@ static struct dst_entry *ip6_dst_check(struct dst_entry *dst, u32 cookie)
>>> * DST_OBSOLETE_FORCE_CHK which forces validation calls down
>>> * into this function always.
>>> */
>>> - if (rt->rt6i_genid != rt_genid_ipv6(dev_net(rt->dst.dev)))
>>> - return NULL;
>>> -
>>> - if (!rt->rt6i_node || (rt->rt6i_node->fn_sernum != cookie))
>>> + if (!rt->rt6i_node || rt_genid_ipv6(dev_net(rt->dst.dev)) != cookie)
>>> return NULL;
>>>
>>> if (rt6_check_expired(rt))
>>>
>>
>> Ok, so now we bump the gen_id every time we add a route and use that as fn_sernum for
>> that route. But this doesn't solve the problem that we are seeing in that a re-lookup
>> of the route still gives us an older route with an older gen_id.
>
> Hmm, this patch completely removes rt6i_genid from rt6_info (first
> hunk). We decide if we need to do the relookup based on the socket's
> cookie and the per-netns serial number of the ipv6 routing tables.
>
Hi Hannes
Right, by you still compare the per-netns serial number to the cookie. The cookie is
typically taken from the route. The route takes it from the per-netns serial number.
So, if you add a route with serial=1 and when the socket looks up that route, it
stashes 1 into the cookie.
Then you add another route and serial = 2. Now the dst_check on the socket fails
(cookie != rt_getid_ipv6(..)) and socket has to re-lookup a route. It gets the same old
route as before with fn_sernum = 1. That's stashed in the cookie again. Next dst_check
is done, the route is invalidated again!.
Am I missing something?
Thanks
-vlad
> Bye,
> Hannes
>
>
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