Re: Bug#267342: kernel-image-2.6.8-1-686-smp: TCP/IP strangeness in 2.6.8

Re: Bug#267342: kernel-image-2.6.8-1-686-smp: TCP/IP strangeness in 2.6.8

[Christoph Hellwig]

Could it be possible OpenBSD doesn't properly deal with the tcp window
scaling changes in 2.6.8? (http://lwn.net/Articles/92727/)


On Sat, Aug 21, 2004 at 10:19:29PM -0400, Kristine Diana Daniels wrote:
> Package: kernel-image-2.6.8-1-686-smp
> Version: 2.6.8-1
> Severity: important
> 
> I have noticed strangeness with the 2.6.8 kernel on both 686-smp
> and k7.
> 1) rsync from 2.6.8 to a 2.6.7 host hangs.
> 2) ssh from 2.6.8 to a 2.6.7 host hangs.
> 3) nntp from 2.6.8 hangs for 52 seconds before proceeding.
> 4) ssh from Openbsd to 2.6.8 hangs after SSH2_MSG_KEX_DH_GEX_REQUEST
> 
> In 1-2 the network topology is as follows
> 2.6.8host <-ethernet-> OpenBSD <-openvpn-> OpenBSD <-ethernet-> 2.6.7host
> In 3 the network topology is as follows
> 2.6.8host <-ethernet-> OpenBSD <-openvpn-> OpenBSD <-internet-> nntp-server
> In 4 the network topology is as follows
> 2.6.8host <-ethernet-> OpenBSD
> 
> In all instances OpenBSD is OpenBSD 3.5+Security updates from up to July.
> The problem does not exhibit itsself with 2.6.7.
> 
> Attached are tcpdumps taken from openbsd and linux for both 2.6.7 and 2.6.8
> of the conversation for nntp.
> tcpdumps for the ssh transactions are available upon request.
> Snapshot of /proc/sys/net/ipv4 also available upon request.
> 
> -- System Information:
> Debian Release: 3.1
>   APT prefers unstable
>   APT policy: (500, 'unstable'), (500, 'testing')
> Architecture: i386 (i686)
> Kernel: Linux 2.6.8-1-686-smp
> Locale: LANG=en_US, LC_CTYPE=en_US
> 
> Versions of packages kernel-image-2.6.8-1-686-smp depends on:
> ii  coreutils [fileutils]         5.2.1-2    The GNU core utilities
> ii  fileutils                     5.2.1-2    The GNU file management utilities 
> ii  initrd-tools                  0.1.73     tools to create initrd image for p
> ii  module-init-tools             3.1-pre5-6 tools for managing Linux kernel mo
> 
> -- no debconf information

Re: Bug#267342: kernel-image-2.6.8-1-686-smp: TCP/IP strangeness in 2.6.8

[Nivedita Singhvi]

Christoph Hellwig wrote:
> Could it be possible OpenBSD doesn't properly deal with the tcp window
> scaling changes in 2.6.8? (http://lwn.net/Articles/92727/)

Unless there is present in the path one of those broken
routers (mangling the window scale option), it's likely
something else. Also, nntp traffic tends to be small and
unaffected by window sizes. Any way to tell if that is so?

Any chance you could make the tcpdumps available, if
this has not already been resolved?

We had a problem with sshd and other apps hanging due
to glibc changes and unsafe signal handling in daemons,
but this seems like something else..

thanks,
Nivedita


>>I have noticed strangeness with the 2.6.8 kernel on both 686-smp
>>and k7.
>>1) rsync from 2.6.8 to a 2.6.7 host hangs.
>>2) ssh from 2.6.8 to a 2.6.7 host hangs.
>>3) nntp from 2.6.8 hangs for 52 seconds before proceeding.
>>4) ssh from Openbsd to 2.6.8 hangs after SSH2_MSG_KEX_DH_GEX_REQUEST
>>
>>In 1-2 the network topology is as follows
>>2.6.8host <-ethernet-> OpenBSD <-openvpn-> OpenBSD <-ethernet-> 2.6.7host
>>In 3 the network topology is as follows
>>2.6.8host <-ethernet-> OpenBSD <-openvpn-> OpenBSD <-internet-> nntp-server
>>In 4 the network topology is as follows
>>2.6.8host <-ethernet-> OpenBSD

Re: Bug#267342: kernel-image-2.6.8-1-686-smp: TCP/IP strangeness in 2.6.8

[Kristine Daniels]

On Wed, Aug 25, 2004 at 02:14:58PM -0700, Nivedita Singhvi wrote:
> Christoph Hellwig wrote:
> >Could it be possible OpenBSD doesn't properly deal with the tcp window
> >scaling changes in 2.6.8? (http://lwn.net/Articles/92727/)
> 
> Unless there is present in the path one of those broken
> routers (mangling the window scale option), it's likely
> something else. Also, nntp traffic tends to be small and
> unaffected by window sizes. Any way to tell if that is so?
> 
> Any chance you could make the tcpdumps available, if
> this has not already been resolved?

Has been temporarily relieved by changing tcp_default_window_size.
(Indicated in updates to the debian bug report)

TCP dumps are available at
http://pakrat.is.an.evilplan.org:5198/267342/

Someone with access to the machine works at IBM.
He will drop you a note if you wish to sametime PD instructions.
Can also recreate on a non-SMP system if so desired.
> 
> We had a problem with sshd and other apps hanging due
> to glibc changes and unsafe signal handling in daemons,
> but this seems like something else..
> 
> thanks,
> Nivedita
> 
> 
> >>I have noticed strangeness with the 2.6.8 kernel on both 686-smp
> >>and k7.
> >>1) rsync from 2.6.8 to a 2.6.7 host hangs.
> >>2) ssh from 2.6.8 to a 2.6.7 host hangs.
> >>3) nntp from 2.6.8 hangs for 52 seconds before proceeding.
> >>4) ssh from Openbsd to 2.6.8 hangs after SSH2_MSG_KEX_DH_GEX_REQUEST
> >>
> >>In 1-2 the network topology is as follows
> >>2.6.8host <-ethernet-> OpenBSD <-openvpn-> OpenBSD <-ethernet-> 2.6.7host
> >>In 3 the network topology is as follows
> >>2.6.8host <-ethernet-> OpenBSD <-openvpn-> OpenBSD <-internet-> 
> >>nntp-server
> >>In 4 the network topology is as follows
> >>2.6.8host <-ethernet-> OpenBSD
> 
> 

-- 
K.D.

Re: Bug#267342: kernel-image-2.6.8-1-686-smp: TCP/IP strangeness in 2.6.8

[David S. Miller]

On Wed, 25 Aug 2004 14:14:58 -0700
Nivedita Singhvi <niv@us.ibm.com> wrote:

> Christoph Hellwig wrote:
> > Could it be possible OpenBSD doesn't properly deal with the tcp window
> > scaling changes in 2.6.8? (http://lwn.net/Articles/92727/)
> 
> Unless there is present in the path one of those broken
> routers (mangling the window scale option), it's likely
> something else.

It was found to in fact be OpenBSD, this bug has been well known
for some time too.  See followups made in this thread.