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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 > > -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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