netdev - Re: [Patch net-next 1/2] net: partially revert dynamic lockdep key changes

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Date:   Sat, 2 May 2020 16:36:19 +0900
From:   Taehee Yoo <ap420073@...il.com>
To:     Cong Wang <xiyou.wangcong@...il.com>
Cc:     Netdev <netdev@...r.kernel.org>,
        syzbot <syzbot+aaa6fa4949cc5d9b7b25@...kaller.appspotmail.com>,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [Patch net-next 1/2] net: partially revert dynamic lockdep key changes

On Fri, 1 May 2020 at 15:02, Cong Wang <xiyou.wangcong@...il.com> wrote:
>

Hi Cong,

> On Thu, Apr 30, 2020 at 12:40 AM Taehee Yoo <ap420073@...il.com> wrote:
> > > +static void vlan_dev_set_lockdep_one(struct net_device *dev,
> > > +                                    struct netdev_queue *txq,
> > > +                                    void *_subclass)
> > > +{
> > > +       lockdep_set_class_and_subclass(&txq->_xmit_lock,
> > > +                                      &vlan_netdev_xmit_lock_key,
> > > +                                      *(int *)_subclass);
> >
> > I think lockdep_set_class() is enough.
> > How do you think about it?
>
> Good catch. I overlooked this one. Is lockdep_set_class() safe
> for vlan stacked on vlan?
>

I think this is safe because of the LLTX flag.
Also, I tested nested VLAN interfaces with lockdep_set_class().
I didn't see any lockdep warning.

Thanks a lot!
Taehee Yoo

> Thanks.