linux-kernel - Re: [PATCH v2 14/14] iommu/tegra: fix device leak on probe

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Message-ID: <aOdyC1toHHIeE4i5@hovoldconsulting.com>
Date: Thu, 9 Oct 2025 10:27:55 +0200
From: Johan Hovold <johan@...nel.org>
To: Thierry Reding <thierry.reding@...il.com>
Cc: Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
	Robin Murphy <robin.murphy@....com>, Sven Peter <sven@...nel.org>,
	Janne Grunau <j@...nau.net>,
	Rob Clark <robin.clark@....qualcomm.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Yong Wu <yong.wu@...iatek.com>,
	Matthias Brugger <matthias.bgg@...il.com>,
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
	Chen-Yu Tsai <wens@...e.org>, Krishna Reddy <vdumpa@...dia.com>,
	iommu@...ts.linux.dev, linux-kernel@...r.kernel.org,
	stable@...r.kernel.org, Thierry Reding <treding@...dia.com>,
	Miaoqian Lin <linmq006@...il.com>
Subject: Re: [PATCH v2 14/14] iommu/tegra: fix device leak on probe_device()

On Thu, Oct 09, 2025 at 09:56:18AM +0200, Thierry Reding wrote:
> On Tue, Oct 07, 2025 at 11:43:27AM +0200, Johan Hovold wrote:

> > @@ -830,10 +830,9 @@ static struct tegra_smmu *tegra_smmu_find(struct device_node *np)
> >  		return NULL;
> >  
> >  	mc = platform_get_drvdata(pdev);
> > -	if (!mc) {
> > -		put_device(&pdev->dev);
> > +	put_device(&pdev->dev);
> > +	if (!mc)
> >  		return NULL;
> > -	}
> >  
> >  	return mc->smmu;
> 
> pdev->dev is what's backing mc, so if we use put_device() here, then the
> MC could go away at any time, right?

Holding a reference to a device does not prevent its driver data from
going away so there is no point in keeping the reference.

But from what I can tell, you don't need to worry about that anyway
since it's the memory controller driver that registers the iommu (and
the driver can't be unbound).

Johan

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