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Date: Thu, 11 Sep 2014 16:32:39 +0200
From: Hannes Frederic Sowa <hannes@...essinduktion.org>
To: Vlad Yasevich <vyasevich@...il.com>
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 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.
Bye,
Hannes
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