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    SubjectRe: Problems with /proc/net/tcp6 - possible bug - ipv6
    Le vendredi 21 janvier 2011 à 22:30 -0800, PK a écrit :
    > Creating many ipv6 connections hits a ceiling on connections/fds ; okay, fine.
    > But in my case I'm seeing millions of entries spring up within a few seconds and
    > then vanish within a few minutes, in /proc/net/tcp6 (vanish due to garbage
    > collection?)
    > Furthermore I can trigger this easily on vanilla kernels from 2.6.36 to
    > 2.6.38-rc1-next-20110121 inside a ubuntu 10.10 amd64 vm, causing the kernel to
    > spew warnings. There is also some corruption in the logs (see kernel-sample.log
    > line 296), but that may be unrelated.
    > More explanation, kernel config of the primary machine I saw this on, sample
    > ruby script to reproduce (inside the ubuntu VMs I apt-get and use ruby-1.9.1),
    > are located at
    > Seems to only affect 64-bit. So far I have not been able to reproduce on 32-bit
    > ubuntu VMs of any kernel version.
    > Seems to only affect IPv6. So far I have not been able to reproduce using IPv4
    > connections (and watching /proc/net/tcp of course).
    > Does not trigger the bug if the connections are made to ::1. Only externally
    > routable local and global IPv6 addresses seem to cause problems.
    > Seems to have been introduced between 2.6.35 and 2.6.36 (see README on github
    > for more kernels I've tried)
    > All the tested Ubuntu VMs are stock 10.10 userland, with vanilla kernels (the
    > latest ubuntu kernel is 2.6.35-something, and my initial test didn't show it
    > suffering from this problem)
    > Originally noticed on separate Gentoo 64-bit non-vm system when doing web
    > benchmarking.
    > not subscribed, so please keep me in cc although I'll try to follow the thread

    Hi PK (Sorry, your real name is hidden)

    I could not reproduce this on current linux-2.6 kernel.

    How many vcpus running in your VM, and memory ?

    Note : a recent commit did fix /proc/net/tcp[6] behavior

    commit 1bde5ac49398a064c753bb490535cfad89e99a5f
    Author: Eric Dumazet <>
    Date: Thu Dec 23 09:32:46 2010 -0800

    tcp: fix listening_get_next()

    Alexey Vlasov found /proc/net/tcp could sometime loop and display
    millions of sockets in LISTEN state.

    In 2.6.29, when we converted TCP hash tables to RCU, we left two
    sk_next() calls in listening_get_next().

    We must instead use sk_nulls_next() to properly detect an end of chain.

    Reported-by: Alexey Vlasov <>
    Signed-off-by: Eric Dumazet <>
    Signed-off-by: David S. Miller <>

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