netdev - Re: [PATCH 1/7] net: ethernet: ti: am65-cpsw: Don't error out in .remove()

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Message-ID: <20231117103949.akpvqfeslyefuzdc@pengutronix.de>
Date: Fri, 17 Nov 2023 11:39:49 +0100
From: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To: Roger Quadros <rogerq@...nel.org>
Cc: netdev@...r.kernel.org, Siddharth Vadapalli <s-vadapalli@...com>,
	kernel@...gutronix.de, Dan Carpenter <dan.carpenter@...aro.org>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>
Subject: Re: [PATCH 1/7] net: ethernet: ti: am65-cpsw: Don't error out in
 .remove()

Hello,

On Fri, Nov 17, 2023 at 11:51:56AM +0200, Roger Quadros wrote:
> On 17/11/2023 11:16, Uwe Kleine-König wrote:
> > Returning early from .remove() with an error code still results in the
> > driver unbinding the device. So the driver core ignores the returned error
> > code and the resources that were not freed are never catched up. In
> > combination with devm this also often results in use-after-free bugs.
> > 
> > In case of the am65-cpsw-nuss driver there is an error path, but it's never
> > taken because am65_cpts_resume() never fails (which however might be
> > another problem). Still make this explicit and drop the early return in
> > exchange for an error message (that is more useful than the error the
> > driver core emits when .remove() returns non-zero).
> > 
> > This prepares changing am65_cpsw_nuss_remove() to return void.
> > 
> > Fixes: 93a76530316a ("net: ethernet: ti: introduce am65x/j721e gigabit eth subsystem driver")
> > Signed-off-by: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
> > ---
> >  drivers/net/ethernet/ti/am65-cpsw-nuss.c | 7 +++++--
> >  1 file changed, 5 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/net/ethernet/ti/am65-cpsw-nuss.c b/drivers/net/ethernet/ti/am65-cpsw-nuss.c
> > index ece9f8df98ae..960cb3fa0754 100644
> > --- a/drivers/net/ethernet/ti/am65-cpsw-nuss.c
> > +++ b/drivers/net/ethernet/ti/am65-cpsw-nuss.c
> > @@ -3007,9 +3007,12 @@ static int am65_cpsw_nuss_remove(struct platform_device *pdev)
> >  
> >  	common = dev_get_drvdata(dev);
> >  
> > -	ret = pm_runtime_resume_and_get(&pdev->dev);
> > +	ret = pm_runtime_get_sync(&pdev->dev);
> 
> Unrelated to this patch but I see pm_runtime_resume_and_get()
> used at multiple places in this driver.
> 
> Would it be wise to replace them all with pm_runtime_get_sync()?

No, in general pm_runtime_resume_and_get() is the variant that is easier
to use because it drops the usage count in the error path. Here however
the error isn't simply propagated and so pm_runtime_get_sync() is
better.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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