netdev - Re: Setting link down hangs the kernel

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Date:   Tue, 10 Jan 2017 16:28:05 +0100
From:   Mason <slash.tmp@...e.fr>
To:     netdev <netdev@...r.kernel.org>
Cc:     Mans Rullgard <mans@...sr.com>,
        Thibaud Cornic <thibaud_cornic@...madesigns.com>,
        Thomas Gambier <thomas_gambier@...madesigns.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Andrew Lunn <andrew@...n.ch>
Subject: Re: Setting link down hangs the kernel

On 10/01/2017 15:36, Mason wrote:

> I'm using kernel v4.9 on a [new] dev board.
> I built a small kernel + rootfs with buildroot 2016.11.1
> eth0 is driven by drivers/net/ethernet/aurora/nb8800.c
> 
> After booting, I just run udhcpc (busybox version)
> Then I set the link down, and the kernel hangs.

So far, I've been unable to reproduce this issue on an older
smp8758 dev board.

# while true
> do
> ip link set dev eth0 down
> sleep 3
> ip link set dev eth0 up
> sleep 3
> let "++XX"
> echo $XX
> done

The output is strange nonetheless:

1
2
3
4
5
[  179.002757] nb8800 26000.ethernet eth0: Link is Up - 100Mbps/Full - flow control rx/tx
6
7
[  192.538648] nb8800 26000.ethernet eth0: Link is Up - 1Gbps/Full - flow control rx/tx
8
9
10
11
12
[  222.284936] nb8800 26000.ethernet eth0: Link is Up - 100Mbps/Full - flow control rx/tx
13
14
^C
# [  235.800851] nb8800 26000.ethernet eth0: Link is Up - 1Gbps/Full - flow control rx/tx


A) I would expect a "Link is Up" message for every "link up" command.
I get only 4 messages for 14 commands. Is that expected?

B) Twice, the PHY was only able to negotiate 100 Mbps, although the
peer supports 1 Gbps. What could cause this?

Regards.