netdev - Re: [PATCH v3 17/41] net: ieee802154: at86rf230: Call the complete helper when a transmission is over

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Date:   Wed, 19 Jan 2022 18:34:49 -0500
From:   Alexander Aring <alex.aring@...il.com>
To:     Miquel Raynal <miquel.raynal@...tlin.com>
Cc:     Stefan Schmidt <stefan@...enfreihafen.org>,
        linux-wpan - ML <linux-wpan@...r.kernel.org>,
        "open list:NETWORKING [GENERAL]" <netdev@...r.kernel.org>,
        "linux-wireless@...r.kernel.org Wireless" 
        <linux-wireless@...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>,
        Michael Hennerich <michael.hennerich@...log.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Varka Bhadram <varkabhadram@...il.com>,
        Xue Liu <liuxuenetmail@...il.com>, Alan Ott <alan@...nal11.us>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH v3 17/41] net: ieee802154: at86rf230: Call the complete
 helper when a transmission is over

Hi,

On Wed, 19 Jan 2022 at 17:56, Miquel Raynal <miquel.raynal@...tlin.com> wrote:
>
> Hi Alexander,
>
> alex.aring@...il.com wrote on Mon, 17 Jan 2022 19:36:39 -0500:
>
> > Hi,
> >
> > On Mon, 17 Jan 2022 at 19:34, Alexander Aring <alex.aring@...il.com> wrote:
> > >
> > > Hi,
> > >
> > > On Mon, 17 Jan 2022 at 06:55, Miquel Raynal <miquel.raynal@...tlin.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@...tlin.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.

Indeed there is no dangled pointer in the irq handling, sorry. I
thought maybe the receive handling but the transceiver is doing a lot
of its own state change handling because of some framebuffer
protection which is not the case.

- Alex