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Date: Tue, 9 Jul 2013 15:11:55 +0800 From: Fan Du <fan.du@...driver.com> To: Neil Horman <nhorman@...driver.com> CC: Vlad Yasevich <vyasevich@...il.com>, <nicolas.dichtel@...nd.com>, <davem@...emloft.net>, <netdev@...r.kernel.org> Subject: Re: [RFC PATCH] sctp: Don't lookup dst if transport dst is still valid Hello Neil On 2013年07月05日 21:03, Neil Horman wrote: > On Thu, Jul 04, 2013 at 10:33:35AM +0800, Fan Du wrote: >> >> >> On 2013年07月03日 21:23, Vlad Yasevich wrote: >>> On 07/02/2013 10:18 PM, Fan Du wrote: >>>> >>>> >>>> On 2013年07月02日 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 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<fan.du@...driver.com> >>>>>> --- >>>>>> 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] = 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 = NULL; >>>>>> + >>>>>> + if (t->dst) { >>>>>> + struct rt6_info *rt = (struct rt6_info *)t->dst; >>>>>> + u32 cookie = 0; >>>>>> + >>>>>> + if ((t->af_specific->sa_family == AF_INET6)&& rt->rt6i_node) >>>>>> + cookie = rt->rt6i_node->fn_sernum; >>>>>> + if (!dst_check(t->dst, cookie)) { >>>>>> + dst_release(t->dst); >>>>>> + t->dst = 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 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 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. >> >> 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 this case, the >> result will be association ABORT. >> > Have you tried this? It seems to me in the situation you describe, deleting a > source address will result in fib_inetaddr_event getting called, which will call ^^^^^^^^^^ This is IPv4 specific. > rt_cache_flush, bumping the rt_genid to get bumped for that network namespace. > That will cause any subsequent calls to dst_check->ip6_dst_check to return NULL ^^^^^^^^^^^^^^^^^ This is IPv6 specific > rather than the cached dst_entry for that transport. The phenomenon(transport->dst got lookup every time for IPv6) I described before could be easily observed by turning on SCTP debug. > Neil > > -- 浮沉随浪只记今朝笑 --fan -- 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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