[Cerowrt-devel] TFO crashes cerowrt 3.7.1-1

Fri Jan 4 16:19:34 EST 2013

+ycheng

On Fri, Jan 4, 2013 at 1:11 PM, Dave Taht <dave.taht at gmail.com> wrote:

> Hmm. I would lean towards there being an issue with the new (freshly
> ported forward to 3.7.1) unaligned checksum code for mips based on
> what you say here. Or an offload...
>
> As for the 239.x multicast issue, hmm... separate issue entirely.
> Probably...
>
> And then there's TFO. I note that in order to use it properly you need
> to turn it on in proc. Last I remember that was
>
> echo 3 > /proc/sys/net/ipv4/tcp_fastopen
>

Correct - to enable the normal use of TFO for both client and server. There
are other flags for advanced usage:
 /* Bit Flags for sysctl_tcp_fastopen */
#define TFO_CLIENT_ENABLE       1
#define TFO_SERVER_ENABLE       2
#define TFO_CLIENT_NO_COOKIE    4 /* Send data-in-SYN w/o cookie */

/* Process SYN data but skip cookie validation */
#define TFO_SERVER_COOKIE_NOT_CHKED     0x100
/* Accept SYN data w/o any cookie option */
#define TFO_SERVER_COOKIE_NOT_REQD      0x200

/* Force enable TFO on all listeners, i.e., not requiring the
 * TCP_FASTOPEN socket option. SOCKOPT1/2 determine how to set max_qlen.
 */
#define TFO_SERVER_WO_SOCKOPT1  0x400
#define TFO_SERVER_WO_SOCKOPT2  0x800
/* Always create TFO child sockets on a TFO listener even when
 * cookie/data not present. (For testing purpose!)
 */
#define TFO_SERVER_ALWAYS       0x1000

> However that's an old memory and there is this tcp_fastopen_key file I
> don't know anything about yet (this is such bleeding edge stuff!)
>
> ... and with tcp_fastopen disabled things should still work right...
> so I'm thinking something else is busted in the stack.
>
> I've also observed a dns slowdown in what I've been testing but hadn't
> dug into packet dumps. (and was assuming, until now, it was due to me
> fiddling with ULAs inside the network) Thanks for digging this deep!
>
> I never said this first attempt at 3.7 for cero was going to be
> perfect, but we've entered a new age of subtle problems here.
>
> I strongly suggest nobody else try this dev build as a default gw, and
> that the TFO folk ignore the noise for now.
>

SG.

Jerry

>
> I just got a 3.7.1 box built on x86_64 so as to a/b some captures.
> Regrettably I'm short on time through the weekend...
>
> On Fri, Jan 4, 2013 at 12:42 PM, Maciej Soltysiak <maciej at soltysiak.com>
> wrote:
> > I am seeing something strange here, with polipo related to TFO but also
> DNS.
> > When I just took 3.7.1-1 and set my windows 7 laptop to use
> gw.home.lan:8123
> > as http proxy it didn't work. What I observed was:
> > A) after quite a while polipo's response to browser was 504 Host
> > www.osnews.com lookup failed: Timeout
> > b) this error in ssh console: Host osnews.com lookup failed: Timeout
> > (131072)
> > c) Disabling TFO by adding option useTCPFastOpen 'false' to config
> 'polipo'
> > 'general' works around the problem
> > d) Alternatively, you can keep TFO enabled in polipo but change option
> > 'dnsUseGethostbyname' from 'reluctantly' to 'true' (!)
> > This is very weird, because TFO is TCP and the DNS queries fired off by
> > polipo are UDP:
> > root at OpenWrt:/tmp/log# tcpdump -n -v -vv -vvv -x -X -s 1500 -i lo
> > 20:21:56.160245 IP (tos 0x0, ttl 64, id 50129, offset 0, flags [DF],
> proto
> > UDP (17), length 60)
> > 127.0.0.1.47304 > 127.0.0.1.53: [bad udp cksum 0xfe3b -> 0xd17f!] 55396+
> A?
> > www.osnews.com. (32)
> > 0x0000: 4500 003c c3d1 4000 4011 78dd 7f00 0001 E..<.. at .@.x.....
> > 0x0010: 7f00 0001 b8c8 0035 0028 fe3b d864 0100 .......5.(.;.d..
> > 0x0020: 0001 0000 0000 0000 0377 7777 066f 736e .........www.osn
> > 0x0030: 6577 7303 636f 6d00 0001 0001 ews.com.....
> > 20:21:56.160319 IP (tos 0x0, ttl 64, id 50130, offset 0, flags [DF],
> proto
> > UDP (17), length 60)
> > 127.0.0.1.47304 > 127.0.0.1.53: [bad udp cksum 0xfe3b -> 0xd164!] 55396+
> > AAAA? www.osnews.com. (32)
> > 0x0000: 4500 003c c3d2 4000 4011 78dc 7f00 0001 E..<.. at .@.x.....
> > 0x0010: 7f00 0001 b8c8 0035 0028 fe3b d864 0100 .......5.(.;.d..
> > 0x0020: 0001 0000 0000 0000 0377 7777 066f 736e .........www.osn
> > 0x0030: 6577 7303 636f 6d00 001c 0001 ews.com.....
> > 20:21:56.169942 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto
> UDP
> > (17), length 123)
> > 127.0.0.1.53 > 127.0.0.1.47304: [bad udp cksum 0xfe7a -> 0x5f73!] 55396
> q:
> > A? www.osnews.com. 1/2/0 www.osnews.com. [29m3s] A 74.86.31.159 ns:
> > osnews.com. [29m3s] NS ns2.swelter.net., osnews.com. [29m3s] NS
> > ns1.swelter.net. (95)
> > 0x0000: 4500 007b 0000 4000 4011 3c70 7f00 0001 E..{.. at .@.<p....
> > 0x0010: 7f00 0001 0035 b8c8 0067 fe7a d864 8180 .....5...g.z.d..
> > 0x0020: 0001 0001 0002 0000 0377 7777 066f 736e .........www.osn
> > 0x0030: 6577 7303 636f 6d00 0001 0001 c00c 0001 ews.com.........
> > 0x0040: 0001 0000 06cf 0004 4a56 1f9f c010 0002 ........JV......
> > 0x0050: 0001 0000 06cf 0011 036e 7332 0773 7765 .........ns2.swe
> > 0x0060: 6c74 6572 036e 6574 00c0 1000 0200 0100 lter.net........
> > 0x0070: 0006 cf00 0603 6e73 31c0 40 ......ns1.@
> > 20:21:56.173901 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto
> UDP
> > (17), length 135)
> > 127.0.0.1.53 > 127.0.0.1.47304: [bad udp cksum 0xfe86 -> 0x8ecb!] 55396
> q:
> > AAAA? www.osnews.com. 1/2/0 www.osnews.com. [54m44s] AAAA
> > 2607:f0d0:1002:62::3 ns: osnews.com. [29m3s] NS ns1.swelter.net.,
> > osnews.com. [29m3s] NS ns2.swelter.net. (107)
> > 0x0000: 4500 0087 0000 4000 4011 3c64 7f00 0001 E..... at .@.<d....
> > 0x0010: 7f00 0001 0035 b8c8 0073 fe86 d864 8180 .....5...s...d..
> > 0x0020: 0001 0001 0002 0000 0377 7777 066f 736e .........www.osn
> > 0x0030: 6577 7303 636f 6d00 001c 0001 c00c 001c ews.com.........
> > 0x0040: 0001 0000 0cd4 0010 2607 f0d0 1002 0062 ........&......b
> > 0x0050: 0000 0000 0000 0003 c010 0002 0001 0000 ................
> > 0x0060: 06cf 0011 036e 7331 0773 7765 6c74 6572 .....ns1.swelter
> > 0x0070: 036e 6574 00c0 1000 0200 0100 0006 cf00 .net............
> > 0x0080: 0603 6e73 32c0 4c ..ns2.L
> > This is the only DNS traffic I saw during the attempts. The tcpdumps have
> > udp bad checksum but when I disabled TFO in polipo, the UDP where still
> bad
> > checksum but they worked.
> > Really weird.
> > p.s. UPNP still works for port forwarding negotiation as it did in
> 3.6.11-4
> > I still couldn't get the UPNP/SSDP broadcasts (udp to 239.255.255.250) to
> > being forwarded between se00 and sw00/sw10. Last time it worked was
> ~3.3.8.
> > I'm starting not to question why it doesn't work, I'm starting to wonder
> why
> > it did work then ;-)
> > Regards,
> > Maciej
> > On Fri, Jan 4, 2013 at 6:33 PM, Dave Taht <dave.taht at gmail.com> wrote:
> >>
> >> On Fri, Jan 4, 2013 at 9:27 AM, Eric Dumazet <edumazet at google.com>
> wrote:
> >> > Sorry, could you give us a copy of the panic stack trace ?
> >>
> >> I will get a serial console up on a wndr3800 by sunday. (sorry, just
> >> landed in california, am in disarray)
> >>
> >> The latest dev build of cero for the wndr3800 and wndr3700v2 is at:
> >>
> >> http://snapon.lab.bufferbloat.net/~cero2/cerowrt/wndr/3.7.1-1/
> >>
> >> --
> >> Dave Täht
> >>
> >> Fixing bufferbloat with cerowrt:
> >> http://www.teklibre.com/cerowrt/subscribe.html
> >> _______________________________________________
> >> Cerowrt-devel mailing list
> >> Cerowrt-devel at lists.bufferbloat.net
> >> https://lists.bufferbloat.net/listinfo/cerowrt-devel
> >
> >
>
>
>
> --
> Dave Täht
>
> Fixing bufferbloat with cerowrt:
> http://www.teklibre.com/cerowrt/subscribe.html
>
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