netdev - Re: [Bugme-new] [Bug 29252] New: IPv6 doesn't work in a kvm guest.

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Date:	Fri, 11 Mar 2011 20:44:39 +0100
From:	Ernst Sjöstrand <ernstp@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	akpm@...ux-foundation.org, netdev@...r.kernel.org,
	bugzilla-daemon@...zilla.kernel.org,
	bugme-daemon@...zilla.kernel.org, slash@...auone-net.jp
Subject: Re: [Bugme-new] [Bug 29252] New: IPv6 doesn't work in a kvm guest.

Hi,

this patch solved the issue I reported. Applied the patch on -rc8.

Regards
//Ernst

On Thu, Mar 10, 2011 at 05:04, David Miller <davem@...emloft.net> wrote:
> From: David Miller <davem@...emloft.net>
> Date: Wed, 09 Mar 2011 19:20:12 -0800 (PST)
>
>> From: David Miller <davem@...emloft.net>
>> Date: Wed, 09 Mar 2011 15:58:18 -0800 (PST)
>>
>>> Ok, the following should address both bugs, #29252 and #30462, please
>>> give it some testing.
>>>
>>> --------------------
>>> ipv6: Don't create clones of nonexthop routes forever.
>>
>> Nevermind, this patch has problems, I'm still debugging and trying to
>> come up with a proper fix.
>>
>> Thanks in advance for your patience.
>
> Ok, I'm more confident in this version of the fix.  It passes all of
> my tests, and I've added instrumentation to make sure various cases
> are performing the operations the way I expect them to.
>
> --------------------
> ipv6: Don't create clones of host routes.
> MIME-Version: 1.0
> Content-Type: text/plain; charset=UTF-8
> Content-Transfer-Encoding: 8bit
>
> Addresses https://bugzilla.kernel.org/show_bug.cgi?id=29252
> Addresses https://bugzilla.kernel.org/show_bug.cgi?id=30462
>
> In commit d80bc0fd262ef840ed4e82593ad6416fa1ba3fc4 ("ipv6: Always
> clone offlink routes.") we forced the kernel to always clone offlink
> routes.
>
> The reason we do that is to make sure we never bind an inetpeer to a
> prefixed route.
>
> The logic turned on here has existed in the tree for many years,
> but was always off due to a protecting CPP define.  So perhaps
> it's no surprise that there is a logic bug here.
>
> The problem is that we canot clone a route that is already a
> host route (ie. has DST_HOST set).  Because if we do, an identical
> entry already exists in the routing tree and therefore the
> ip6_rt_ins() call is going to fail.
>
> This sets off a series of failures and high cpu usage, because when
> ip6_rt_ins() fails we loop retrying this operation a few times in
> order to handle a race between two threads trying to clone and insert
> the same host route at the same time.
>
> Fix this by simply using the route as-is when DST_HOST is set.
>
> Reported-by: slash@...auone-net.jp
> Reported-by: Ernst Sjöstrand <ernstp@...il.com>
> Signed-off-by: David S. Miller <davem@...emloft.net>
> ---
>  net/ipv6/route.c |    4 +++-
>  1 files changed, 3 insertions(+), 1 deletions(-)
>
> diff --git a/net/ipv6/route.c b/net/ipv6/route.c
> index 904312e..e7db701 100644
> --- a/net/ipv6/route.c
> +++ b/net/ipv6/route.c
> @@ -739,8 +739,10 @@ restart:
>
>        if (!rt->rt6i_nexthop && !(rt->rt6i_flags & RTF_NONEXTHOP))
>                nrt = rt6_alloc_cow(rt, &fl->fl6_dst, &fl->fl6_src);
> -       else
> +       else if (!(rt->dst.flags & DST_HOST))
>                nrt = rt6_alloc_clone(rt, &fl->fl6_dst);
> +       else
> +               goto out2;
>
>        dst_release(&rt->dst);
>        rt = nrt ? : net->ipv6.ip6_null_entry;
> --
> 1.7.4.1
>
>
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