netdev - Re: [PATCH net-next] net: ethernet: mtk_wed: fix possible deadlock if mtk_wed_wo

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Date:   Sun, 4 Dec 2022 16:09:21 +0100
From:   Lorenzo Bianconi <lorenzo@...nel.org>
To:     Leon Romanovsky <leon@...nel.org>
Cc:     netdev@...r.kernel.org, nbd@....name, john@...ozen.org,
        sean.wang@...iatek.com, Mark-MC.Lee@...iatek.com,
        davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
        pabeni@...hat.com, matthias.bgg@...il.com,
        linux-mediatek@...ts.infradead.org, lorenzo.bianconi@...hat.com
Subject: Re: [PATCH net-next] net: ethernet: mtk_wed: fix possible deadlock
 if mtk_wed_wo_init fails

> On Fri, Dec 02, 2022 at 06:36:33PM +0100, Lorenzo Bianconi wrote:
> > Introduce __mtk_wed_detach() in order to avoid a possible deadlock in
> > mtk_wed_attach routine if mtk_wed_wo_init fails.
> > 
> > Fixes: 4c5de09eb0d0 ("net: ethernet: mtk_wed: add configure wed wo support")
> > Signed-off-by: Lorenzo Bianconi <lorenzo@...nel.org>
> > ---
> >  drivers/net/ethernet/mediatek/mtk_wed.c     | 24 ++++++++++++++-------
> >  drivers/net/ethernet/mediatek/mtk_wed_mcu.c | 10 ++++++---
> >  drivers/net/ethernet/mediatek/mtk_wed_wo.c  |  3 +++
> >  3 files changed, 26 insertions(+), 11 deletions(-)
> 
> <...>
> 
> > diff --git a/drivers/net/ethernet/mediatek/mtk_wed_mcu.c b/drivers/net/ethernet/mediatek/mtk_wed_mcu.c
> > index f9539e6233c9..b084009a32f9 100644
> > --- a/drivers/net/ethernet/mediatek/mtk_wed_mcu.c
> > +++ b/drivers/net/ethernet/mediatek/mtk_wed_mcu.c
> > @@ -176,6 +176,9 @@ int mtk_wed_mcu_send_msg(struct mtk_wed_wo *wo, int id, int cmd,
> >  	u16 seq;
> >  	int ret;
> >  
> > +	if (!wo)
> > +		return -ENODEV;
> 
> <...>
> 
> >  static void
> >  mtk_wed_wo_hw_deinit(struct mtk_wed_wo *wo)
> >  {
> > +	if (!wo)
> > +		return;
> 
> How are these changes related to the written in deadlock?
> How is it possible to get internal mtk functions without valid wo?

Hi Leon,

if mtk_wed_rro_alloc() fails in mtk_wed_attach(), we will end up running
__mtk_wed_detach() when wo struct is not allocated yet (wo is allocated in
mtk_wed_wo_init()).
Moreover __mtk_wed_detach() can run mtk_wed_wo_reset() and mtk_wed_wo_deinit()
so we will need to check if wo pointer is properly set. We will face the same
issue if wo allocation fails in mtk_wed_wo_init routine.
If we remove the deadlock we need to take into account even these conditions.

Regards,
Lorenzo

> 
> Thanks
> 
> > +
> >  	/* disable interrupts */
> >  	mtk_wed_wo_set_isr(wo, 0);
> >  
> > -- 
> > 2.38.1
> > 

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