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

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Message-ID: <Y420B4/IpwFHJAck@lore-desk>
Date:   Mon, 5 Dec 2022 10:04:07 +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 Dec 05, Leon Romanovsky wrote:
> On Sun, Dec 04, 2022 at 04:09:21PM +0100, Lorenzo Bianconi wrote:
> > > 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()).
> 
> IMHO, it is a culprit, proper error unwind means that you won't call to
> uninit functions for something that is not initialized yet. It is better
> to fix it instead of adding "if (!wo) ..." checks.

So, iiuc, you would prefer to do something like:

__mtk_wed_detach()
{
	...
	if (mtk_wed_get_rx_capa(dev) && wo) {
		mtk_wed_wo_reset(dev);
		mtk_wed_free_rx_rings(dev);
		mtk_wed_wo_deinit(hw);
	}
	...
	
Right? I am fine both ways :)

> 
> > Moreover __mtk_wed_detach() can run mtk_wed_wo_reset() and mtk_wed_wo_deinit()
> 
> This is another side of same coin. If you can run them in parallel, you
> need locking protection and ability to cancel work, so nothing is going
> to be executed once cleanup succeeded.

Sorry, I did not get what you mean here with 'in parallel'. __mtk_wed_detach()
always run with hw_lock mutex help in both mtk_wed_attach() or
mtk_wed_detach().

Regards,
Lorenzo

> 
> These were my 2 cents, totally IMHO.
> 
> Thanks

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