From mboxrd@z Thu Jan 1 00:00:00 1970 From: Fan Du Subject: Re: [RFC PATCH] sctp: Don't lookup dst if transport dst is still valid Date: Thu, 4 Jul 2013 10:33:35 +0800 Message-ID: <51D4DEFF.8030305@windriver.com> References: <1372747174-23580-1-git-send-email-fan.du@windriver.com> <51D2E3C8.5050100@gmail.com> <51D389F9.4030804@windriver.com> <51D425B7.20204@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: , , , To: Vlad Yasevich Return-path: Received: from mail1.windriver.com ([147.11.146.13]:37375 "EHLO mail1.windriver.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932206Ab3GDCfg (ORCPT ); Wed, 3 Jul 2013 22:35:36 -0400 In-Reply-To: <51D425B7.20204@gmail.com> Sender: netdev-owner@vger.kernel.org List-ID: 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 ZE= RO, >>>> as a result ip6_dst_check always fail out. This behaviour makes >>>> transport->dst useless, because every sctp_packet_transmit must lo= ok >>>> for valid dst(Is this what supposed to be?) >>>> >>>> One aggressive way is to call rt_genid_bump which invalid all dst = 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_node= ) >>>> + 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 th= at, >>> 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 issue. 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 ds= t as NULL. Then we lookup dst by sctp_transport_route, and in there we initi= ate 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, an= d return valid dst without bothering to lookup dst again. BUT, suppose when deleting the source address of this dst after transpo= rt->dst_cookie has been well initialized. transport->dst_cookie still holds rt->rt6i_n= ode->fn_sernum, meaning ip6_dst_check will return valid dst, which it shouldn't in this= case, the result will be association ABORT. Other way is invalid all transport->dst which using the deleting addres= s as source address without bumping gen_id, problem is the traverse times depends heavily o= n 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 al= ways seems to pass it as 0. > > Yes, ipv4 will bump the gen_id thus invalidating all routes (there h= as been disagreement about it). > IPv6 doesn't do that. In ipv6, when the addresses are added or remov= ed, routes are also added or removed and > any time the route is added it will have a new serial number. So, yo= u 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 serial= 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 mos= t other Layer 4 protocol simply rely on ip6_route_output/ip6_dst_lookup_flow to grab dst every t= ime sending data out. 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_add= r >> *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.h >> 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 union >> 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; >>>> } >>>> >>>> >>> >>> >> > > --=20 =E6=B5=AE=E6=B2=89=E9=9A=8F=E6=B5=AA=E5=8F=AA=E8=AE=B0=E4=BB=8A=E6=9C=9D= =E7=AC=91 --fan