netdev - Kernel crash while using tc script

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Message-ID: <CAGK4HS_cCQPJwXVoCuZAa2zHtPnXO+ar5Wpg_azyxc5Efv4Mwg@mail.gmail.com>
Date:	Tue, 19 May 2015 13:11:59 -0700
From:	Vijay Subramanian <subramanian.vijay@...il.com>
To:	netdev <netdev@...r.kernel.org>, tgraf <tgraf@...g.ch>,
	Daniel Borkmann <dborkman@...hat.com>
Subject: Kernel crash while using tc script

Hi,

It seems latest net-next kernel crashes while unloading modules.
Please see simple script below to reproduce the crash.

===============================

#!/bin/bash

while true; do

# modules will be loaded automatically

tc qdisc add dev eth1 root handle 1: prio

tc filter add dev eth1 parent 1: u32 match u32 0 0  flowid 1

tc qdisc del dev eth1 root

rmmod cls_u32

rmmod sch_prio

done

=========================

It seems there is some refcounting or locking issue issue. I am unable
to easily post the dump but sometimes it points to crashes in various
functions in prio_class_ops  (sch_prio.c), such as prio_walk(),
prio_dump_class etc. Probably, sch_prio call back functions are
invoked when they should not be.

I bisected this down to following commit:

commit 78fd1d0ab072d4d9b5f0b7c14a1516665170b565
Author: Thomas Graf <tgraf@...g.ch>
Date:   Tue Oct 21 22:05:38 2014 +0200
netlink: Re-add locking to netlink_lookup() and seq walker

If there are suggestions for me to try or you need more info, let me know.

Thanks,
Vijay
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