Date:   Sat, 5 Oct 2019 18:40:24 +0900
From:   Taehee Yoo <ap420073@...il.com>
To:     Johannes Berg <johannes@...solutions.net>
Cc:     David Miller <davem@...emloft.net>,
        Netdev <netdev@...r.kernel.org>, linux-wireless@...r.kernel.org,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        j.vosburgh@...il.com, vfalico@...il.com,
        Andy Gospodarek <andy@...yhouse.net>,
        Jiří Pírko <jiri@...nulli.us>,
        sd@...asysnail.net, Roopa Prabhu <roopa@...ulusnetworks.com>,
        saeedm@...lanox.com, manishc@...vell.com, rahulv@...vell.com,
        kys@...rosoft.com, haiyangz@...rosoft.com,
        Stephen Hemminger <stephen@...workplumber.org>,
        sashal@...nel.org, hare@...e.de, varun@...lsio.com,
        ubraun@...ux.ibm.com, kgraul@...ux.ibm.com,
        Jay Vosburgh <jay.vosburgh@...onical.com>,
        Cody Schuffelen <schuffelen@...gle.com>, bjorn@...k.no
Subject: Re: [PATCH net v4 00/12] net: fix nested device bugs

On Tue, 1 Oct 2019 at 16:39, Johannes Berg <johannes@...solutions.net> wrote:
>

Hi,

> On Sun, 2019-09-29 at 17:31 +0900, Taehee Yoo wrote:
>
> > virt_wifi case is a little bit different case.
>
> Well, arguably, it was also just missing this - it just looks different
> :)
>
> > I add the last patch that is to fix refcnt leaks in the virt_wifi module.
> > The way to fix this is to add notifier routine.
> > The notifier routine could delete lower device before deleting
> > virt_wifi device.
> > If virt_wifi devices are nested, notifier would work recursively.
> > At that time, it would make stack memory overflow.
> >
> > Actually, before this patch, virt_wifi doesn't have the same problem.
> > So, I will update a comment in a v5 patch.
>
> OK, sure.
>
> > Many other devices use this way to avoid wrong nesting configuration.
> > And I think it's a good way.
> > But we should think about the below configuration.
> >
> > vlan5
> >    |
> > virt_wifi4
> >    |
> > vlan3
> >    |
> > virt_wifi2
> >    |
> > vlan1
> >    |
> > dummy0
> >
> > That code wouldn't avoid this configuration.
> > And all devices couldn't avoid this config.
>
> Good point, so then really that isn't useful to check - most people
> won't try to set it up that way (since it's completely useless) and if
> they do anyway too much nesting would be caught by your patchset here.
>

Yes, Thanks!

> > I have been considering this case, but I couldn't make a decision yet.
> > Maybe common netdev function is needed to find the same device type
> >  in their graph.
>
> I don't think it's worthwhile just to prevent somebody from making a
> configuration that we think now is nonsense. Perhaps they do have some
> kind of useful use-case for it ...
>

I agree with your opinion.

> > This is a little bit different question for you.
> > I found another bug in virt_wifi after my last patch.
> > Please test below commands
> >     ip link add dummy0 type dummy
> >     ip link add vw1 link dummy0 type virt_wifi
> >     ip link add vw2 link vw1 type virt_wifi
> >     modprobe -rv virt_wifi
> >
> > Then, you can see the warning messages.
> > If SET_NETDEV_DEV() is deleted in the virt_wifi_newlink(),
> > you can avoid that warning message.
> > But I'm not sure about it's safe to remove that.
> > I would really appreciate it if you let me know about that.
>
> Hmm, I don't see any warnings. SET_NETDEV_DEV() should be there though.
Okay, thanks. I will do not remove SET_NETDEV_DEV() in a v5 patch.
> Do you see the same if you stack it with something else inbetween? If
> not, I guess preventing virt_wifi from stacking on top of itself would
> be sufficient ...
>

Yes, the below test commands will make warning messages.
So, I will add a new patch for this without removing SET_NETDEV_DEV().

Reproducer :
    ip link add dummy0 type dummy
    ip link add vw1 link dummy0 type virt_wifi
    ip link add vlan2 link vw1 type vlan id 1
    ip link add vw3 link vlan2 type virt_wifi
    modprobe -rv virt_wifi

Messages:
[12734.236946] sysfs group 'byte_queue_limits' not found for kobject 'tx-0'
[12734.238862] WARNING: CPU: 1 PID: 19710 at fs/sysfs/group.c:280
sysfs_remove_group+0x11b/0x170
[ ... ]
12734.256132] Call Trace:
[12734.256430]  netdev_queue_update_kobjects+0x1f5/0x340
[12734.257025]  netdev_unregister_kobject+0x142/0x1d0
[12734.257580]  rollback_registered_many+0x618/0xc80
[12734.258175]  ? notifier_call_chain+0x90/0x160
[12734.258688]  ? generic_xdp_install+0x310/0x310
[12734.259208]  ? netdev_upper_dev_unlink+0x114/0x180
[12734.259791]  unregister_netdevice_many.part.126+0x13/0x1b0
[12734.260434]  __rtnl_link_unregister+0x156/0x320
[12734.260967]  ? rtnl_unregister_all+0x120/0x120
[ ... ]
[12734.283395] sysfs group 'power' not found for kobject 'vw3'
[12734.284081] WARNING: CPU: 1 PID: 19710 at fs/sysfs/group.c:280
sysfs_remove_group+0x11b/0x170
[ ... ]
[12734.337509] sysfs group 'statistics' not found for kobject 'vw3'
[12734.338375] WARNING: CPU: 1 PID: 19710 at fs/sysfs/group.c:280
sysfs_remove_group+0x11b/0x170
[ ... ]
[12734.391687] sysfs group 'wireless' not found for kobject 'vw3'
[12734.392525] WARNING: CPU: 1 PID: 19710 at fs/sysfs/group.c:280
sysfs_remove_group+0x11b/0x170
[ ... ]

> johannes
>

Thanks,
Taehee Yoo

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