netdev - Re: [offlist] Re: Crash in netlink/sk_filter_trim

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Date:   Fri, 17 Aug 2018 13:25:44 +0100
From:   Peter Robinson <pbrobinson@...il.com>
To:     Russell King - ARM Linux <linux@...linux.org.uk>
Cc:     Marc Haber <mh+netdev@...schlus.de>,
        linux-arm-kernel@...ts.infradead.org, netdev@...r.kernel.org,
        labbott@...hat.com, Eric Dumazet <eric.dumazet@...il.com>,
        Daniel Borkmann <daniel@...earbox.net>
Subject: Re: [offlist] Re: Crash in netlink/sk_filter_trim_cap on ARMv7 on 4.18rc1

On Thu, Aug 16, 2018 at 11:58 PM, Russell King - ARM Linux
<linux@...linux.org.uk> wrote:
> On Thu, Aug 16, 2018 at 10:35:16PM +0200, Marc Haber wrote:
>> On Mon, Jun 25, 2018 at 05:41:27PM +0100, Peter Robinson wrote:
>> > So with that and the other fix there was no improvement, with those
>> > and the BPF JIT disabled it works, I'm not sure if the two patches
>> > have any effect with the JIT disabled though.
>>
>> I can confirm the crash with the released 4.18.1 on Banana Pi, and I can
>> also confirm that disabling BPF JIT makes the Banana Pi work again.,
>
> Hi,
>
> I'm afraid that the information in the crash dumps is insufficient
> to be able to work very much out about these crashes.
>
> We need a recipe (kernel configuration and what userspace is doing)
> so that it's possible to recreate the crash, or we need responses
> to requests for information - I requested the disassembly of
> sk_filter_trim_cap and the BPF code dump via setting a sysctl back
> in early July.  Without this, as I say, I don't see how this problem
> can be progressed.

I can provide a kernel config [1] but I've not had enough time to sit
down and get the rest of the stuff and debug it due to a combination
of travel and other priorities.

> If the problem is at boot, one way to set the sysctl would be to
> hack the kernel and explicitly initialise the sysctl to '2', or
> boot with init=/bin/sh, then manually mount /proc, set the sysctl,
> and then "exec /sbin/init" from that shell.  (Remember there's no
> job control in that shell, so ^z, ^c, etc do not work.)

It starts to happen in the early kernel boot long before we get to any
userspace across a number of ARMv7 devices (RPi2/3, BeagleBone and
AllWinner H3 based devices at least).

[1] https://pbrobinson.fedorapeople.org/kernel-armv7hl.config