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From:   Alexander Aring <alex.aring@gmail.com>
Date:   Wed, 19 Jan 2022 19:19:35 -0500
Message-ID: <CAB_54W7Cs8=zBokk_ka-LWAOoSQy-M-aHxn5kjCckfO5EqQGJg@mail.gmail.com>
Subject: Re: [PATCH v3 17/41] net: ieee802154: at86rf230: Call the complete
 helper when a transmission is over
To:     Miquel Raynal <miquel.raynal@bootlin.com>
Cc:     Stefan Schmidt <stefan@datenfreihafen.org>,
        linux-wpan - ML <linux-wpan@vger.kernel.org>,
        "open list:NETWORKING [GENERAL]" <netdev@vger.kernel.org>,
        "linux-wireless@vger.kernel.org Wireless" 
        <linux-wireless@vger.kernel.org>,
        David Girault <david.girault@qorvo.com>,
        Romuald Despres <romuald.despres@qorvo.com>,
        Frederic Blain <frederic.blain@qorvo.com>,
        Nicolas Schodet <nico@ni.fr.eu.org>,
        Michael Hennerich <michael.hennerich@analog.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Varka Bhadram <varkabhadram@gmail.com>,
        Xue Liu <liuxuenetmail@gmail.com>, Alan Ott <alan@signal11.us>,
        Thomas Petazzoni <thomas.petazzoni@bootlin.com>
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Hi,

On Wed, 19 Jan 2022 at 18:34, Alexander Aring <alex.aring@gmail.com> wrote:
>
> Hi,
>
> On Wed, 19 Jan 2022 at 17:56, Miquel Raynal <miquel.raynal@bootlin.com> wrote:
> >
> > Hi Alexander,
> >
> > alex.aring@gmail.com wrote on Mon, 17 Jan 2022 19:36:39 -0500:
> >
> > > Hi,
> > >
> > > On Mon, 17 Jan 2022 at 19:34, Alexander Aring <alex.aring@gmail.com> wrote:
> > > >
> > > > Hi,
> > > >
> > > > On Mon, 17 Jan 2022 at 06:55, Miquel Raynal <miquel.raynal@bootlin.com> wrote:
> > > > >
> > > > > ieee802154_xmit_complete() is the right helper to call when a
> > > > > transmission is over. The fact that it completed or not is not really a
> > > > > question, but drivers must tell the core that the completion is over,
> > > > > even if it was canceled. Do not call ieee802154_wake_queue() manually,
> > > > > in order to let full control of this task to the core.
> > > > >
> > > > > By using the complete helper we also avoid leacking the skb structure.
> > > > >
> > > > > Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
> > > > > ---
> > > > >  drivers/net/ieee802154/at86rf230.c | 2 +-
> > > > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > > >
> > > > > diff --git a/drivers/net/ieee802154/at86rf230.c b/drivers/net/ieee802154/at86rf230.c
> > > > > index 583f835c317a..1941e1f3d2ef 100644
> > > > > --- a/drivers/net/ieee802154/at86rf230.c
> > > > > +++ b/drivers/net/ieee802154/at86rf230.c
> > > > > @@ -343,7 +343,7 @@ at86rf230_async_error_recover_complete(void *context)
> > > > >         if (ctx->free)
> > > > >                 kfree(ctx);
> > > > >
> > > > > -       ieee802154_wake_queue(lp->hw);
> > > > > +       ieee802154_xmit_complete(lp->hw, lp->tx_skb, false);
> > > >
> > > > also this lp->tx_skb can be a dangled pointer, after xmit_complete()
> > > > we need to set it to NULL in a xmit_error() we can check on NULL
> > > > before calling kfree_skb().
> > > >
> > >
> > > forget the NULL checking, it's already done by core. However in some
> > > cases this is called with a dangled pointer on lp->tx_skb.
> >
> > Actually I don't see why tx_skb is dangling?
> >
> > There is no function that could accesses lp->tx_skb between the free
> > operation and the next call to ->xmit() which does a lp->tx_skb = skb.
> > Am I missing something?
> >
>
> look into at86rf230_sync_state_change() it is a sync over async and
> the function "at86rf230_async_error_recover_complete()" is a generic
> error handling to recover from a state change. It's e.g. being used in
> e.g. at86rf230_start() which can occur in cases which are not xmit
> related.
>

which means there is more being broken that we should not simply call
to wake the queue in non-transmit cases...

- Alex