netdev - Re: [PATCH net] vxlan: do not destroy fdb if register

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Date:   Tue, 25 Jun 2019 22:03:12 -0700
From:   Roopa Prabhu <roopa@...ulusnetworks.com>
To:     Taehee Yoo <ap420073@...il.com>
Cc:     David Miller <davem@...emloft.net>, Netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net] vxlan: do not destroy fdb if register_netdevice() is failed

On Tue, Jun 25, 2019 at 9:08 AM Taehee Yoo <ap420073@...il.com> wrote:
>
> On Tue, 25 Jun 2019 at 13:12, Roopa Prabhu <roopa@...ulusnetworks.com> wrote:
> >
>
> Hi Roopa,
>
> Thank you for the review!
>
> > On Sun, Jun 23, 2019 at 7:18 PM Taehee Yoo <ap420073@...il.com> wrote:
> > >
> > > On Mon, 24 Jun 2019 at 03:07, David Miller <davem@...emloft.net> wrote:
> > > >
> > >
> > > Hi David,
> > >
> > > Thank you for the review!
> > >
> > > > From: Taehee Yoo <ap420073@...il.com>
> > > > Date: Thu, 20 Jun 2019 20:51:08 +0900
> > > >
> > > > > __vxlan_dev_create() destroys FDB using specific pointer which indicates
> > > > > a fdb when error occurs.
> > > > > But that pointer should not be used when register_netdevice() fails because
> > > > > register_netdevice() internally destroys fdb when error occurs.
> > > > >
> > > > > In order to avoid un-registered dev's notification, fdb destroying routine
> > > > > checks dev's register status before notification.
> > > >
> > > > Simply pass do_notify as false in this failure code path of __vxlan_dev_create(),
> > > > thank you.
> > >
> > > Failure path of __vxlan_dev_create() can't handle do_notify in that case
> > > because if register_netdevice() fails it internally calls
> > > ->ndo_uninit() which is
> > > vxlan_uninit().
> > > vxlan_uninit() internally calls vxlan_fdb_delete_default() and it callls
> > > vxlan_fdb_destroy().
> > > do_notify of vxlan_fdb_destroy() in vxlan_fdb_delete_default() is always true.
> > > So, failure path of __vxlan_dev_create() doesn't have any opportunity to
> > > handle do_notify.
> >
> >
> > I don't see register_netdevice calling ndo_uninit in case of all
> > errors. In the case where it does not,
> > does your patch leak the fdb entry ?.
> >
> > Wondering if we should just use vxlan_fdb_delete_default with a notify
> > flag to delete the entry if exists.
> > Will that help ?
> >
> > There is another commit that touched this code path:
> > commit 6db9246871394b3a136cd52001a0763676563840
> >
> > Author: Petr Machata <petrm@...lanox.com>
> > Date:   Tue Dec 18 13:16:00 2018 +0000
> >     vxlan: Fix error path in __vxlan_dev_create()
>
> I have checked up failure path of register_netdevice().
> Yes, this patch leaks fdb entry.
> There are 3 failure cases in the register_netdevice().
> A. error occurs before calling ->ndo_init().
> it doesn't call ->ndo_uninit().
> B. error occurs after calling ->ndo_init().
> it calls ->ndo_uninit() and dev->reg_state is NETREG_UNINITIALIZED.
> C. error occurs after registering netdev. it calls rollback_registered().
> rollback_registered() internally calls ->ndo_uninit()
> and dev->reg_state is NETREG_UNREGISTERING.
>
> A panic due to these problem could be fixed by using
> vxlan_fdb_delete_default() with notify flag.
> But notification problem could not be fixed clearly
> because of the case C.

yes, you are right. The notification issue still remains.

>
> I don't have clear solution for the case C.
> Please let me know, if you have any good idea for fixing the case C.

One option is a variant of fdb create. alloc the fdb  but don't assign
it to the vxlan dev.
__vxlan_dev_create
             create fdb entry
             register_netdevice
             rtnl_configure_link
             link fdb to vxlan
             fdb notify


Yet another option is moving fdb create after register_netdevice
__vxlan_dev_create
             register_netdevice
             rtnl_configure_link
             create fdb entry
             fdb notify
But if fdb create fails, user-space will see , NEWLINK + DELLINK when
creating a vxlan device and that seems weird.