netdev - Re: nf_nat_pptp 4.12.3 kernel lockup/reboot

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Date:   Fri, 25 Aug 2017 10:15:56 +0300
From:   Denys Fedoryshchenko <nuclearcat@...learcat.com>
To:     Florian Westphal <fw@...len.de>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: nf_nat_pptp 4.12.3 kernel lockup/reboot

On 2017-08-25 08:21, Florian Westphal wrote:
> Denys Fedoryshchenko <nuclearcat@...learcat.com> wrote:
>> >>> I am trying to upgrade kernel 4.11.8 to 4.12.3 (it is a nat/router, handling
>> >>> approx 2gbps of pppoe users traffic) and noticed that after while server
>> >>> rebooting(i have set reboot on panic and etc).
>> >>> I can't run serial console, and in pstore / netconsole there is nothing.
>> >>> Best i got is some very short message about softlockup in ipmi, but as
>> >>> storage very limited there - it is near useless.
>> >>>
>> >>> By preliminary testing (can't do it much, as it's production) - it seems
>> >>> following lines causing issue, they worked in 4.11.8 and no more in 4.12.3.
>> >>
>> >>Wild guess here, does this help?
>> >>
>> >>diff --git a/net/netfilter/nf_conntrack_helper.c
>> >>b/net/netfilter/nf_conntrack_helper.c
>> >>--- a/net/netfilter/nf_conntrack_helper.c
>> >>+++ b/net/netfilter/nf_conntrack_helper.c
>> >>@@ -266,6 +266,8 @@ int __nf_ct_try_assign_helper(struct nf_conn *ct,
>> >>struct nf_conn *tmpl,
>> >>                help = nf_ct_helper_ext_add(ct, helper, flags);
>> >>                if (help == NULL)
>> >>                        return -ENOMEM;
>> >>+              	if (!nf_ct_ext_add(ct, NF_CT_EXT_NAT, flags));
>> >
>> >sigh, stupid typo, should be no ';' at the end above.
>> Sorry, is there any plans to push this to 4.12 stable queue?
> 
> No, sorry, this patch adds the extension for all connections
> that use a helper, but the nat extension is only used/required by pptp
> helper (and masquerade).
> 
> Thing is that this patch should not be needed, I will have
> to review pptp again, maybe i missed a case where the extension is not
> added.
> 
> Do you happen to have an oops backtrace?
> 
> That might speed this up a bit.
There is nothing in netconsole, and also nothing ERST pstore, i found 
reason just by guessing.
Its totally headless also (no screen, no serial console).
I can try to attach USB serial for serial console, but not sure it will 
help.
If there is any other way to catch - i can try it, but as it's 
production server, so i can't "crash it" more than once per day.