Re: [bug] stuck localhost TCP connections, v2.6.26-rc3+

On Sat, 31 May 2008, Ingo Molnar wrote:

* Ingo Molnar <mingo@xxxxxxx> wrote:

ah, in retrospect i realized that this test had one flaw: some of the
systems i the build cluster already ran a newer kernel and hence were
targets for this bug.

so i turned off CONFIG_TCP_CONG_CUBIC on all the testboxes and
rebooted the cluster boxes into 2.6.25, and the hung sockets are now
gone. (about 150 successful iterations)

i did another change as well: i removed the localhost distcc
component. I'll reinstate that now to make sure it's really related to
TCP_CONG_CUBIC and not to localhost networking.

ok, once i added back the localhost distcc component and the hung kernel
build + stuck TCP socket bug happened again overnight:

Active Internet connections (w/o servers)
Proto Recv-Q Send-Q Local Address Foreign Address State
tcp 72187 0 10.0.1.14:3632 10.0.1.14:47910 ESTABLISHED
tcp 0 174464 10.0.1.14:47910 10.0.1.14:3632 ESTABLISHED

so it seems distcc over localhost was the aspect that made it fail.

_Perhaps_ what matters is to have the new post-rc3 TCP code on _both_
sides of the connection. But that is just a theory - it could be timing,
etc.

Btw, does your distcc perhaps happen enable TCP_DEFER_ACCEPT (there were
some post 2.6.25 changes into it)?

--
i.
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