netdev - Re: [PATCH wpan-next v2 09/11] net: mac802154: Introduce a synchronous API for MLME commands

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Date:   Sun, 15 May 2022 19:03:53 -0400
From:   Alexander Aring <aahringo@...hat.com>
To:     Miquel Raynal <miquel.raynal@...tlin.com>
Cc:     Alexander Aring <alex.aring@...il.com>,
        Stefan Schmidt <stefan@...enfreihafen.org>,
        linux-wpan - ML <linux-wpan@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Network Development <netdev@...r.kernel.org>,
        David Girault <david.girault@...vo.com>,
        Romuald Despres <romuald.despres@...vo.com>,
        Frederic Blain <frederic.blain@...vo.com>,
        Nicolas Schodet <nico@...fr.eu.org>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH wpan-next v2 09/11] net: mac802154: Introduce a
 synchronous API for MLME commands

Hi,

On Sun, May 15, 2022 at 6:28 PM Alexander Aring <aahringo@...hat.com> wrote:
>
> Hi,
>
> On Thu, May 12, 2022 at 10:34 AM Miquel Raynal
> <miquel.raynal@...tlin.com> wrote:
> >
> > This is the slow path, we need to wait for each command to be processed
> > before continuing so let's introduce an helper which does the
> > transmission and blocks until it gets notified of its asynchronous
> > completion. This helper is going to be used when introducing scan
> > support.
> >
> > Signed-off-by: Miquel Raynal <miquel.raynal@...tlin.com>
> > ---
> >  net/mac802154/ieee802154_i.h |  1 +
> >  net/mac802154/tx.c           | 25 +++++++++++++++++++++++++
> >  2 files changed, 26 insertions(+)
> >
> > diff --git a/net/mac802154/ieee802154_i.h b/net/mac802154/ieee802154_i.h
> > index a057827fc48a..f8b374810a11 100644
> > --- a/net/mac802154/ieee802154_i.h
> > +++ b/net/mac802154/ieee802154_i.h
> > @@ -125,6 +125,7 @@ extern struct ieee802154_mlme_ops mac802154_mlme_wpan;
> >  void ieee802154_rx(struct ieee802154_local *local, struct sk_buff *skb);
> >  void ieee802154_xmit_sync_worker(struct work_struct *work);
> >  int ieee802154_sync_and_hold_queue(struct ieee802154_local *local);
> > +int ieee802154_mlme_tx(struct ieee802154_local *local, struct sk_buff *skb);
> >  netdev_tx_t
> >  ieee802154_monitor_start_xmit(struct sk_buff *skb, struct net_device *dev);
> >  netdev_tx_t
> > diff --git a/net/mac802154/tx.c b/net/mac802154/tx.c
> > index 38f74b8b6740..ec8d872143ee 100644
> > --- a/net/mac802154/tx.c
> > +++ b/net/mac802154/tx.c
> > @@ -128,6 +128,31 @@ int ieee802154_sync_and_hold_queue(struct ieee802154_local *local)
> >         return ieee802154_sync_queue(local);
> >  }
> >
> > +int ieee802154_mlme_tx(struct ieee802154_local *local, struct sk_buff *skb)
> > +{
> > +       int ret;
> > +
> > +       /* Avoid possible calls to ->ndo_stop() when we asynchronously perform
> > +        * MLME transmissions.
> > +        */
> > +       rtnl_lock();
>
> I think we should make an ASSERT_RTNL() here, the lock needs to be
> earlier than that over the whole MLME op. MLME can trigger more than

not over the whole MLME_op, that's terrible to hold the rtnl lock so
long... so I think this is fine that some netdev call will interfere
with this transmission.
So forget about the ASSERT_RTNL() here, it's fine (I hope).

> one message, the whole sync_hold/release queue should be earlier than
> that... in my opinion is it not right to allow other messages so far
> an MLME op is going on? I am not sure what the standard says to this,
> but I think it should be stopped the whole time? All those sequence

Whereas the stop of the netdev queue makes sense for the whole mlme-op
(in my opinion).

- Alex