From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vlad Yasevich Subject: Re: [RFC PATCH] sctp: Don't lookup dst if transport dst is still valid Date: Tue, 09 Jul 2013 11:11:40 -0400 Message-ID: <51DC282C.9090007@gmail.com> References: <1372747174-23580-1-git-send-email-fan.du@windriver.com> <51D2E3C8.5050100@gmail.com> <51D389F9.4030804@windriver.com> <51D425B7.20204@gmail.com> <51D4DEFF.8030305@windriver.com> <51D6D3A0.7050106@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: nhorman@tuxdriver.com, nicolas.dichtel@6wind.com, davem@davemloft.net, netdev@vger.kernel.org To: Fan Du Return-path: Received: from mail-qa0-f49.google.com ([209.85.216.49]:41453 "EHLO mail-qa0-f49.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753864Ab3GIPLn (ORCPT ); Tue, 9 Jul 2013 11:11:43 -0400 Received: by mail-qa0-f49.google.com with SMTP id hu16so2975875qab.15 for ; Tue, 09 Jul 2013 08:11:42 -0700 (PDT) In-Reply-To: <51D6D3A0.7050106@gmail.com> Sender: netdev-owner@vger.kernel.org List-ID: On 07/05/2013 10:09 AM, Vlad Yasevich wrote: > On 07/03/2013 10:33 PM, Fan Du wrote: >> >> >> On 2013=E5=B9=B407=E6=9C=8803=E6=97=A5 21:23, Vlad Yasevich wrote: >>> On 07/02/2013 10:18 PM, Fan Du wrote: >>>> >>>> >>>> On 2013=E5=B9=B407=E6=9C=8802=E6=97=A5 22:29, Vlad Yasevich wrote: >>>>> On 07/02/2013 02:39 AM, Fan Du wrote: >>>>>> When sctp sits on IPv6, sctp_transport_dst_check pass cookie as = ZERO, >>>>>> as a result ip6_dst_check always fail out. This behaviour makes >>>>>> transport->dst useless, because every sctp_packet_transmit must = look >>>>>> for valid dst(Is this what supposed to be?) >>>>>> >>>>>> One aggressive way is to call rt_genid_bump which invalid all ds= t to >>>>>> make new dst for transport, apparently it also hurts others. >>>>>> I'm sure this may not be the best for all, so any commnets? >>>>>> >>>>>> Signed-off-by: Fan Du >>>>>> --- >>>>>> include/net/sctp/sctp.h | 18 ++++++++++++------ >>>>>> net/sctp/ipv6.c | 2 ++ >>>>>> 2 files changed, 14 insertions(+), 6 deletions(-) >>>>>> >>>>>> diff --git a/include/net/sctp/sctp.h b/include/net/sctp/sctp.h >>>>>> index cd89510..f05af01 100644 >>>>>> --- a/include/net/sctp/sctp.h >>>>>> +++ b/include/net/sctp/sctp.h >>>>>> @@ -719,14 +719,20 @@ static inline void sctp_v4_map_v6(union >>>>>> sctp_addr *addr) >>>>>> addr->v6.sin6_addr.s6_addr32[2] =3D htonl(0x0000ffff); >>>>>> } >>>>>> >>>>>> -/* The cookie is always 0 since this is how it's used in the >>>>>> - * pmtu code. >>>>>> - */ >>>>>> +/* Set cookie with the right one for IPv6 and zero for others *= / >>>>>> static inline struct dst_entry *sctp_transport_dst_check(struct >>>>>> sctp_transport *t) >>>>>> { >>>>>> - if (t->dst && !dst_check(t->dst, 0)) { >>>>>> - dst_release(t->dst); >>>>>> - t->dst =3D NULL; >>>>>> + >>>>>> + if (t->dst) { >>>>>> + struct rt6_info *rt =3D (struct rt6_info *)t->dst; >>>>>> + u32 cookie =3D 0; >>>>>> + >>>>>> + if ((t->af_specific->sa_family =3D=3D AF_INET6) && rt->rt6i_no= de) >>>>>> + cookie =3D rt->rt6i_node->fn_sernum; >>>>>> + if (!dst_check(t->dst, cookie)) { >>>>>> + dst_release(t->dst); >>>>>> + t->dst =3D NULL; >>>>>> + } >>>>>> } >>>>> >>>>> I think it would be better if we stored the dst_cookie in the >>>>> transport structure and initialized it at lookup time. If you do = that, >>>>> then if the route table changes, we'd correctly detect it without >>>>> artificially bumping rt_genid (and hurting ipv4). >>>> >>>> Hi Vlad/Neil >>>> >>>> Is this what you mean? >>> >>> Yes, exactly. >>> >> >> Hi Vlad >> >> I thinks twice about below patch, this is actually a chicken-egg iss= ue. >> Look below scenario: >> (1) The first time we push packet through a transport, dst_cookie = is 0, >> so sctp_transport_dst_check also pass cookie as 0, then return= dst >> as NULL. >> Then we lookup dst by sctp_transport_route, and in there we >> initiate dst_cookie >> with rt->rt6i_node->fn_sernum >> >> (2) Then the next time we push packet through this transport again= , >> we pass dst_cookie(rt->rt6i_node->fn_sernum) to ip6_dst_check,= and >> return valid dst without bothering to lookup dst again. > > No, if the route was removed rt6i_node will be NULL, and NULL will be > returned from ip6_dst_check(). If the route still exists then we'll > compare the serial number with a cookie. > >> >> BUT, suppose when deleting the source address of this dst after >> transport->dst_cookie >> has been well initialized. transport->dst_cookie still holds >> rt->rt6i_node->fn_sernum, >> meaning ip6_dst_check will return valid dst, which it shouldn't in t= his >> case, the >> result will be association ABORT. > > No, removing the address cause the route for that prefix to be remove= d > as well. This will set rt6i_node to NULL. > >> >> Other way is invalid all transport->dst which using the deleting add= ress >> as source address >> without bumping gen_id, problem is the traverse times depends heavil= y on >> transport number, >> and also need to take account locking issue it will introduce. >> >> > >> > No, you are not missing anything. IPv4 doesn't use the cookie and >> always seems to pass it as 0. >> > >> > Yes, ipv4 will bump the gen_id thus invalidating all routes (ther= e >> has been disagreement about it). >> > IPv6 doesn't do that. In ipv6, when the addresses are added or >> removed, routes are also added or removed and >> > any time the route is added it will have a new serial number. So,= you >> don't have to disturb ipv4 cache when ipv6 routing info changes. >> >> Thank you very much for your explanation! >> >> IPv6 don't bump gen_id, when adding/deleting address, and tag an ser= ial >> number with each route. >> Doing this way loose the semantic of dst_check, because SCTP depends= no >> dst_check fulfill its >> duty to actually check whether the holding dst is still valid, well = most >> other Layer 4 protocol >> simply rely on ip6_route_output/ip6_dst_lookup_flow to grab dst ever= y >> time sending data out. > > Look at how other protocols (tcp, dccp) do this. It is sufficient to > cache the route serial number into the dst_cookie at the time the rou= te > was lookup-up and cached. Then the cookie is passed to dst_check to > validate the route. Hi Fan Have you tried the updated patch you sent? Based on what the tcp/udp=20 code is doing, the updated patch should work correctly. If it does, ca= n=20 you re-post with attribution/sign-off Thanks -vlad > > -vlad >> >> So please pronounce a final judgment. >> >>> -vlad >>> >>>> >>>> diff --git a/include/net/sctp/sctp.h b/include/net/sctp/sctp.h >>>> index cd89510..0a646a5 100644 >>>> --- a/include/net/sctp/sctp.h >>>> +++ b/include/net/sctp/sctp.h >>>> @@ -724,7 +724,7 @@ static inline void sctp_v4_map_v6(union sctp_a= ddr >>>> *addr) >>>> */ >>>> static inline struct dst_entry *sctp_transport_dst_check(struct >>>> sctp_transport *t) >>>> { >>>> - if (t->dst && !dst_check(t->dst, 0)) { >>>> + if (t->dst && !dst_check(t->dst, t->dst_cookie)) { >>>> dst_release(t->dst); >>>> t->dst =3D NULL; >>>> } >>>> diff --git a/include/net/sctp/structs.h b/include/net/sctp/structs= =2Eh >>>> index 1bd4c41..cafdd19 100644 >>>> --- a/include/net/sctp/structs.h >>>> +++ b/include/net/sctp/structs.h >>>> @@ -946,6 +946,8 @@ struct sctp_transport { >>>> __u64 hb_nonce; >>>> >>>> struct rcu_head rcu; >>>> + >>>> + u32 dst_cookie; >>>> }; >>>> >>>> struct sctp_transport *sctp_transport_new(struct net *, const unio= n >>>> sctp_addr *, >>>> diff --git a/net/sctp/ipv6.c b/net/sctp/ipv6.c >>>> index 8ee553b..82a420f 100644 >>>> --- a/net/sctp/ipv6.c >>>> +++ b/net/sctp/ipv6.c >>>> @@ -350,6 +350,7 @@ out: >>>> struct rt6_info *rt; >>>> rt =3D (struct rt6_info *)dst; >>>> t->dst =3D dst; >>>> + t->dst_cookie =3D rt->rt6i_node ? rt->rt6i_node->fn_sernum >>>> : 0; >>>> SCTP_DEBUG_PRINTK("rt6_dst:%pI6 rt6_src:%pI6\n", >>>> &rt->rt6i_dst.addr, &fl6->saddr); >>>> } else { >>>> >>>> >>>> >>>> >>>> >>>>> -vlad >>>>> >>>>>> >>>>>> return t->dst; >>>>>> diff --git a/net/sctp/ipv6.c b/net/sctp/ipv6.c >>>>>> index 8ee553b..cfae77e 100644 >>>>>> --- a/net/sctp/ipv6.c >>>>>> +++ b/net/sctp/ipv6.c >>>>>> @@ -137,6 +137,8 @@ static int sctp_inet6addr_event(struct >>>>>> notifier_block *this, unsigned long ev, >>>>>> break; >>>>>> } >>>>>> >>>>>> + /* invalid all transport dst forcing to look up new dst */ >>>>>> + rt_genid_bump(net); >>>>>> return NOTIFY_DONE; >>>>>> } >>>>>> >>>>>> >>>>> >>>>> >>>> >>> >>> >> >