netdev - Re: mvneta: oops in __rcu_read

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Date:	Mon, 16 Sep 2013 01:56:46 -0700
From:	Ethan Tuttle <ethan@...antuttle.com>
To:	Willy Tarreau <w@....eu>
Cc:	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	Andrew Lunn <andrew@...n.ch>,
	Jason Cooper <jason@...edaemon.net>, netdev@...r.kernel.org,
	Ezequiel Garcia <ezequiel.garcia@...e-electrons.com>,
	Gregory Clément 
	<gregory.clement@...e-electrons.com>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: mvneta: oops in __rcu_read_lock on mirabox

Hi guys.  Here's the config I was building with:

https://gist.github.com/anonymous/6578139

It's based on the one I found in archlinuxarm's git repo.  I didn't
change any of the options - at least, not manually.

Thanks for the follow up!

Ethan


On Sun, Sep 15, 2013 at 11:50 PM, Willy Tarreau <w@....eu> wrote:
> Hi Thomas,
>
> On Sun, Sep 15, 2013 at 08:57:01PM +0200, Thomas Petazzoni wrote:
>> Hello Ethan,
>>
>> On Sat, 14 Sep 2013 18:05:32 -0700, Ethan Tuttle wrote:
>> > When I upgraded my mirabox from 3.11-rc4 to 3.11, I started seeing
>> > oopses while receiving network traffic (see below).  Sending a flood
>> > ping will trigger the oops within a few minutes.
>> >
>> > The stack looks similar, but not identical to, the one reported
>> > earlier by Jochen De Smet[1].  In my case the PC is always
>> > __rcu_read_lock.
>> >
>> > A git bisect found a878764 "Merge
>> > git://git.kernel.org/pub/scm/linux/kernel/git/davem/net" to be the
>> > first bad commit... interesting, because neither of the merge parents
>> > produce the oops.  I rebased the net changes onto the other merge
>> > parent and bisected that series, which identified 702821f "net: revert
>> > 8728c544a9c ("net: dev_pick_tx() fix")" as the first bad commit.
>> > Indeed, reverting 702821f from 3.11 produces a kernel which stands up
>> > to a ping flood for hours.
>> >
>> > Each of the times I reproduced this, it was identified as "Unhandled
>> > prefetch abort: unknown 25 (0x409) at 0xc0036ea0", except once when I
>> > got "unknown 16 (0x400)".
>> >
>> > I'm assuming this is an mvneta bug that was exposed by 702821f.
>> > That's just a guess, and I don't have the skills to debug this any
>> > further.  In any case, I figured the maintainers would want to know
>> > about it.
>>
>> Thanks a lot for the report and the detailed investigation.
>> Unfortunately, I don't have Armada 370 hardware with me this week, so
>> I'm unable to test and reproduce the issue.
>>
>> However, I've added a bunch of Armada 370 people/maintainers in Cc,
>> hopefully they can at least try to reproduce and confirm that reverting
>> this patch makes the problem go away, which would confirm that we
>> should look for a bug in the mvneta driver around this problem.
>
> I'm currently testing on 3.11.1 (which I had here) and am not getting
> any issue after 50M packets. My kernel is running in thumb mode and
> without SMP.
>
> Ethan, we'll need your config I guess.
>
> Thanks,
> Willy
>
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