Re: [PATCH net v4 07/12] macvlan: use dynamic lockdep key instead of subclass

From: Johannes Berg <johannes@sipsolutions.net>
To: Taehee Yoo <ap420073@gmail.com>
Cc: "David Miller" <davem@davemloft.net>,
	Netdev <netdev@vger.kernel.org>,
	linux-wireless@vger.kernel.org,
	"Jakub Kicinski" <jakub.kicinski@netronome.com>,
	j.vosburgh@gmail.com, vfalico@gmail.com,
	"Andy Gospodarek" <andy@greyhouse.net>,
	"Jiří Pírko" <jiri@resnulli.us>,
	sd@queasysnail.net, "Roopa Prabhu" <roopa@cumulusnetworks.com>,
	saeedm@mellanox.com, manishc@marvell.com, rahulv@marvell.com,
	kys@microsoft.com, haiyangz@microsoft.com,
	"Stephen Hemminger" <stephen@networkplumber.org>,
	sashal@kernel.org, hare@suse.de, varun@chelsio.com,
	ubraun@linux.ibm.com, kgraul@linux.ibm.com,
	"Jay Vosburgh" <jay.vosburgh@canonical.com>,
	"Cody Schuffelen" <schuffelen@google.com>,
	bjorn@mork.no
Subject: Re: [PATCH net v4 07/12] macvlan: use dynamic lockdep key instead of subclass
Date: Mon, 07 Oct 2019 13:41:14 +0200	[thread overview]
Message-ID: <bb48fca5a5ffb0a877b2bff8de07ec8090b63427.camel@sipsolutions.net> (raw)
In-Reply-To: <CAMArcTVeFGqA2W26=rBD5KkjRpFB6gjSgXj8dp+WWrrwJ7pr-A@mail.gmail.com> (sfid-20191005_111343_179256_72415A7E)

On Sat, 2019-10-05 at 18:13 +0900, Taehee Yoo wrote:
> 
> If we place lockdep keys into "struct net_device", this macro would be a
> little bit modified and reused. And driver code shape will not be huge
> changed. I think this way is better than this v4 way.
> So I will try it.

What I was thinking was that if we can do this for every VLAN netdev,
why shouldn't we do it for *every* netdev unconditionally? Some code
could perhaps even be simplified if this was just a general part of
netdev allocation.

> > But it seems to me the whole nesting also has to be applied here?
> > 
> > __dev_xmit_skb:
> >  * qdisc_run_begin()
> >  * sch_direct_xmit()
> >    * HARD_TX_LOCK(dev, txq, smp_processor_id());
> >    * dev_hard_start_xmit() // say this is VLAN
> >      * dev_queue_xmit() // on real_dev
> >        * __dev_xmit_skb // recursion on another netdev
> > 
> > Now if you have VLAN-in-VLAN the whole thing will recurse right?
> > 
> 
> I have checked on this routine.
> Only xmit_lock(HARD_TX_LOCK) could be nested. other
> qdisc locks(runinng, busylock) will not be nested. 

OK, I still didn't check it too closely I guess, or got confused which
lock I should look at.

> This patch already
> handles the _xmit_lock key. so I think there is no problem.

Right

> But I would like to place four lockdep keys(busylock, address,
> running, _xmit_lock) into "struct net_device" because of code complexity.
> 
> Let me know if I misunderstood anything.

Nothing to misunderstand - I was just asking/wondering why the qdisc
locks were not treated the same way.

johannes