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

From: Miquel Raynal <miquel.raynal@bootlin.com>
To: Alexander Aring <alex.aring@gmail.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>
Subject: Re: [PATCH v3 17/41] net: ieee802154: at86rf230: Call the complete helper when a transmission is over
Date: Wed, 19 Jan 2022 23:56:00 +0100	[thread overview]
Message-ID: <20220119235600.48173f5b@xps13> (raw)
In-Reply-To: <CAB_54W5Uu9_hpqmeL0MC+1ps=yfn2j0-o46cBL7BeBxKXKHa4w@mail.gmail.com>

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?

Thanks,
Miquèl