On Tue, Aug 15, 2017 at 3:42 PM, Shaohua Li <s...@kernel.org> wrote: > On Tue, Aug 15, 2017 at 07:08:31AM -0700, Tom Herbert wrote: >> On Mon, Aug 14, 2017 at 7:52 PM, Shaohua Li <s...@kernel.org> wrote: >> > On Fri, Aug 11, 2017 at 06:00:20PM -0700, Tom Herbert wrote: >> >> On Thu, Aug 10, 2017 at 12:13 PM, Shaohua Li <s...@kernel.org> wrote: >> >> > On Thu, Aug 10, 2017 at 11:30:51AM -0700, Tom Herbert wrote: >> >> >> On Thu, Aug 10, 2017 at 9:30 AM, Shaohua Li <s...@kernel.org> wrote: >> >> >> > On Wed, Aug 09, 2017 at 09:40:08AM -0700, Tom Herbert wrote: >> >> >> >> On Mon, Jul 31, 2017 at 3:19 PM, Shaohua Li <s...@kernel.org> wrote: >> >> >> >> > From: Shaohua Li <s...@fb.com> >> >> >> >> > >> >> >> >> > Please see below tcpdump output: >> >> >> >> > 21:00:48.109122 IP6 (flowlabel 0x43304, hlim 64, next-header TCP >> >> >> >> > (6) payload length: 40) fec0::5054:ff:fe12:3456.55804 > >> >> >> >> > fec0::5054:ff:fe12:3456.5555: Flags [S], cksum 0x0529 (incorrect >> >> >> >> > -> 0xf56c), seq 3282214508, win 43690, options [mss >> >> >> >> > 65476,sackOK,TS val 2500903437 ecr 0,nop,wscale 7], length 0 >> >> >> >> > 21:00:48.109381 IP6 (flowlabel 0xd827f, hlim 64, next-header TCP >> >> >> >> > (6) payload length: 40) fec0::5054:ff:fe12:3456.5555 > >> >> >> >> > fec0::5054:ff:fe12:3456.55804: Flags [S.], cksum 0x0529 >> >> >> >> > (incorrect -> 0x49ad), seq 1923801573, ack 3282214509, win 43690, >> >> >> >> > options [mss 65476,sackOK,TS val 2500903437 ecr >> >> >> >> > 2500903437,nop,wscale 7], length 0 >> >> >> >> > 21:00:48.109548 IP6 (flowlabel 0x43304, hlim 64, next-header TCP >> >> >> >> > (6) payload length: 32) fec0::5054:ff:fe12:3456.55804 > >> >> >> >> > fec0::5054:ff:fe12:3456.5555: Flags [.], cksum 0x0521 (incorrect >> >> >> >> > -> 0x1bdf), seq 1, ack 1, win 342, options [nop,nop,TS val >> >> >> >> > 2500903437 ecr 2500903437], length 0 >> >> >> >> > 21:00:48.109823 IP6 (flowlabel 0x43304, hlim 64, next-header TCP >> >> >> >> > (6) payload length: 62) fec0::5054:ff:fe12:3456.55804 > >> >> >> >> > fec0::5054:ff:fe12:3456.5555: Flags [P.], cksum 0x053f (incorrect >> >> >> >> > -> 0xb8b1), seq 1:31, ack 1, win 342, options [nop,nop,TS val >> >> >> >> > 2500903437 ecr 2500903437], length 30 >> >> >> >> > 21:00:48.109910 IP6 (flowlabel 0xd827f, hlim 64, next-header TCP >> >> >> >> > (6) payload length: 32) fec0::5054:ff:fe12:3456.5555 > >> >> >> >> > fec0::5054:ff:fe12:3456.55804: Flags [.], cksum 0x0521 (incorrect >> >> >> >> > -> 0x1bc1), seq 1, ack 31, win 342, options [nop,nop,TS val >> >> >> >> > 2500903437 ecr 2500903437], length 0 >> >> >> >> > 21:00:48.110043 IP6 (flowlabel 0xd827f, hlim 64, next-header TCP >> >> >> >> > (6) payload length: 56) fec0::5054:ff:fe12:3456.5555 > >> >> >> >> > fec0::5054:ff:fe12:3456.55804: Flags [P.], cksum 0x0539 >> >> >> >> > (incorrect -> 0xb726), seq 1:25, ack 31, win 342, options >> >> >> >> > [nop,nop,TS val 2500903438 ecr 2500903437], length 24 >> >> >> >> > 21:00:48.110173 IP6 (flowlabel 0x43304, hlim 64, next-header TCP >> >> >> >> > (6) payload length: 32) fec0::5054:ff:fe12:3456.55804 > >> >> >> >> > fec0::5054:ff:fe12:3456.5555: Flags [.], cksum 0x0521 (incorrect >> >> >> >> > -> 0x1ba7), seq 31, ack 25, win 342, options [nop,nop,TS val >> >> >> >> > 2500903438 ecr 2500903438], length 0 >> >> >> >> > 21:00:48.110211 IP6 (flowlabel 0xd827f, hlim 64, next-header TCP >> >> >> >> > (6) payload length: 32) fec0::5054:ff:fe12:3456.5555 > >> >> >> >> > fec0::5054:ff:fe12:3456.55804: Flags [F.], cksum 0x0521 >> >> >> >> > (incorrect -> 0x1ba7), seq 25, ack 31, win 342, options >> >> >> >> > [nop,nop,TS val 2500903438 ecr 2500903437], length 0 >> >> >> >> > 21:00:48.151099 IP6 (flowlabel 0x43304, hlim 64, next-header TCP >> >> >> >> > (6) payload length: 32) fec0::5054:ff:fe12:3456.55804 > >> >> >> >> > fec0::5054:ff:fe12:3456.5555: Flags [.], cksum 0x0521 (incorrect >> >> >> >> > -> 0x1ba6), seq 31, ack 26, win 342, options [nop,nop,TS val >> >> >> >> > 2500903438 ecr 2500903438], length 0 >> >> >> >> > 21:00:49.110524 IP6 (flowlabel 0x43304, hlim 64, next-header TCP >> >> >> >> > (6) payload length: 56) fec0::5054:ff:fe12:3456.55804 > >> >> >> >> > fec0::5054:ff:fe12:3456.5555: Flags [P.], cksum 0x0539 (incorrect >> >> >> >> > -> 0xb324), seq 31:55, ack 26, win 342, options [nop,nop,TS val >> >> >> >> > 2500904438 ecr 2500903438], length 24 >> >> >> >> > 21:00:49.110637 IP6 (flowlabel 0xb34d5, hlim 64, next-header TCP >> >> >> >> > (6) payload length: 20) fec0::5054:ff:fe12:3456.5555 > >> >> >> >> > fec0::5054:ff:fe12:3456.55804: Flags [R], cksum 0x0515 (incorrect >> >> >> >> > -> 0x668c), seq 1923801599, win 0, length 0 >> >> >> >> > >> >> >> >> > The flowlabel of reset packet (0xb34d5) and flowlabel of normal >> >> >> >> > packet >> >> >> >> > (0xd827f) are different. This causes our router doesn't correctly >> >> >> >> > close tcp >> >> >> >> > connection. The patches try to fix the issue. >> >> >> >> > >> >> >> >> Shaohua, >> >> >> >> >> >> >> >> Can you give some more detail about what the router doesn't close >> >> >> >> the >> >> >> >> TCP connection means? I'm guessing the problem is either: 1) the >> >> >> >> router is maintaining connection state that includes the flow label >> >> >> >> in >> >> >> >> a connection tuple. 2) some router in the path is maintaining >> >> >> >> connection state, but when the flow label changes the flow's packet >> >> >> >> are routed through a different router that doesn't have a state for >> >> >> >> the flow it drops the packet. #1 should be easily fix in the router, >> >> >> >> flow labels cannot be used as state. #2 is the known problem that >> >> >> >> stateful firewalls have killed our ability to use multihoming. >> >> >> > >> >> >> > The #2 is exactly the problem we saw. >> >> >> > >> >> >> >> Another consideration is that sk_txhash is also used in routing >> >> >> >> decisions by the local host (flow label is normally derived from >> >> >> >> txhash). If you want to ensure that connections are routed >> >> >> >> consistently for timewait state you might need sk_txhash saved also. >> >> >> > >> >> >> > As far as I understood, we don't use sk_txhash for routing >> >> >> > selection. The code >> >> >> > does routing selection with flowlabel user configured, at that time >> >> >> > we don't >> >> >> > derive fl6.flowlabel from skb->hash (which is from sk_txhash). The >> >> >> > code always >> >> >> > does routing selection first and then uses ip6_make_flowlabel to >> >> >> > build packet >> >> >> > data where we derive flowlabel from skb->hash. >> >> >> > >> >> >> That is assuming one particular use case. Generally, if you want to >> >> >> ensure all packets for a flow take the same path you'll need tx_hash >> >> >> and make it persistent (disable flow bender). For instance, if you >> >> >> were doing UDP encapsulation like in VXLAN the UDP source port >> >> >> selection is unaffected by saved flow label for the lifetime of the >> >> >> flow. So we would still hit #2 in that case and the stateful device >> >> >> doesn't see whole flow. It might be just as easy to move tx_hash in >> >> >> skc_common so that it's available in TW state for this purpose. Then >> >> >> when moving to TW state just copy the tx_hash. >> >> > >> >> > Hi Tom, >> >> > >> >> > My original implementation is to add a tx_hash in tw sock, we then copy >> >> > sock's >> >> > tx_hash to the tw tx_hash. This does makes things simplier. One concern >> >> > from >> >> > Eric is this will increase the size of tw sock. If we move tx_hash to >> >> > skc_common, all sock size will increase, is this acceptable? >> >> >> >> I think that can only be measured by how critical it is to >> >> persistently route all packets the same exact way for every >> >> connection. Page one of the IP book clearly states that IP packets can >> >> be dropped, duplicated, or received out of order. Received OOO implies >> >> that packet for the same flow are allowed to take different paths. The >> >> requirement that packets for the same flow must always take the same >> >> path through the network was created by stateful middleboxes-- it's >> >> not inherent in the architecture of IP networking. Unfortunately, >> >> we're seeing this become more and more of a problem as more devices >> >> are multi-homed (like smart phones) and these network requirement >> >> cripple our ability to take advantage of features like that. >> >> >> >> Personally, I wish the middleboxes fix the problem they created, but I >> >> suppose we need to be pragmatic at least in the short term. >> > >> > Hmm, I still hesitate to add a new field in skc_common. Fixing current >> > problem >> > looks propriate in current stage. I'd defer fixing the generic issue till >> > it's >> > necessary. >> > >> Shaohua, >> >> An alternative would be to not initialize sk_txhash, but instead defer >> hash computation to use flow dissector in the TX path when the hash is >> needed (to get flow label, src port for UDP encap, route for >> multipath, etc.). At the first hash computation in TX path the result >> in sk_txhash. TW state there is no socket so flow dissector is >> always used but that should yield the same hash. No extra fields would >> be needed and additional cost is negligible. > > Hi Tom, > > Did you mean revert 877d1f6291f8(net: Set sk_txhash from a random number)? > This > could fix the issue. So in normal case we calculate the sk_txhash using flow > dissector but in negative routing case we use the random hash, is this what > you > want? > No. What you'd want is something like a sysctl that sets an alternate mode for sk_txhash processing. sk_txhash is derived from flow dissector for the first TX packet and then it's never allowed to change. Maybe this should be called persistent-hash mode.
> There seems to have other bug in this side. From my understanding, commit > 265f94ff54d6(net: Recompute sk_txhash on negative routing advice) tries to > select a different route. But the multipath selection code > (rt6_multipath_select) doesn't use sk_txhash or skb->hash, it does use > fl6.flowlabel, but that is the flowlabel user sets. So looks like the commit > doesn't change anything. > The routing functions typically don't use sock of skbuff, but use flow structs instead. It may be reasonable to add a hash to those. > What's the 'src port for UDP encap'? I can't find the code setting skb->hash > to sk_txhash in UDP side. > udp_flow_src_port is function call by UDP encaps to set source port. This is call skb_get_hash. sk_set_txhash is function to set txhash right now to random value. skb_set_hash_from_sk set skb->hash when skbuff is owned by socket (skb_set_owner_w). Thanks, Tom > Thanks, > Shaohua
