Re: [BUG] MVPP2 driver exploding in presence of a tap interface

Marc,

On Mon, Oct 29, 2018 at 03:05:53PM +0000, Marc Zyngier wrote:

This is a follow-up on the conversation Thomas and I had last week at 
ELC, with me ranting at the sorry state of the MVPP2 driver.

Triggering this is dead simple:
- Add a macvtap to one of the MVPP2 interfaces
- Bring it online
- Watch the kernel exploding and memory being corrupted

You don't even need anything listening on the tap interface, just its
simple existence triggers it. I use a similar setup on a large variety 
of machines, and this box is the only one that catches fire. Removing
the macvtap interface makes it (more) reliable.

Given that I cannot reproduce this issue on any other ARM (32 or 64bit)
platform, including other Marvell stuff, I can only conclude that the
MVPP2 driver is responsible for this.

Example crash and .config below (4.19 vanilla, as linux/master dies in
new and wonderful ways on this box). I'm looking forward to testing any
idea you may have.

I used a 4.19 vanilla kernel, with both your configuration and mine,
on 2 different Macchiatobins, but was unable to trigger the issue:

  # ip link set eth0 up
  # ip link add link eth0 name macvtap0 type macvtap
  # ip link set macvtap0 up

I can even configure the eth0/macvtap0 interfaces, and use them
generating or receiving tcp/udp/icmp traffic.

(I also made other tests using macvtap and tap interfaces).

How much memory do you have on the board? What version of ATF are you
using? Version of U-Boot?

Antoine

-- 
Antoine Ténart, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com