linux-kernel - Re: [PATCH] drm: sti: fix device leaks at component probe

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Message-ID: <aQnhtkIG9-A7yH-H@hovoldconsulting.com>
Date: Tue, 4 Nov 2025 12:21:26 +0100
From: Johan Hovold <johan@...nel.org>
To: Raphaël Gallais-Pou <rgallaispou@...il.com>
Cc: Alain Volmat <alain.volmat@...s.st.com>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
	stable@...r.kernel.org,
	Benjamin Gaignard <benjamin.gaignard@...labora.com>
Subject: Re: [PATCH] drm: sti: fix device leaks at component probe

On Fri, Oct 31, 2025 at 06:10:46PM +0100, Raphaël Gallais-Pou wrote:

> Le Mon, Sep 22, 2025 at 02:20:12PM +0200, Johan Hovold a écrit :
> > Make sure to drop the references taken to the vtg devices by
> > of_find_device_by_node() when looking up their driver data during
> > component probe.
> 
> Markus suggested “Prevent device leak in of_vtg_find()” as commit
> summary.

Markus has gotten himself banned from the mailing lists some years ago
and even if he is now back with a new mail address most of us still
ignore him.

I prefer the Subject as it stands since it captures when the leaks
happens, but I don't mind mentioning of_vtg_find() instead if you
insist.

> > Note that holding a reference to a platform device does not prevent its
> > driver data from going away so there is no point in keeping the
> > reference after the lookup helper returns.
> > 
> > Fixes: cc6b741c6f63 ("drm: sti: remove useless fields from vtg structure")
> > Cc: stable@...r.kernel.org	# 4.16
> > Cc: Benjamin Gaignard <benjamin.gaignard@...labora.com>
> > Signed-off-by: Johan Hovold <johan@...nel.org>
> > ---
> >  drivers/gpu/drm/sti/sti_vtg.c | 7 ++++++-
> >  1 file changed, 6 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/sti/sti_vtg.c b/drivers/gpu/drm/sti/sti_vtg.c
> > index ee81691b3203..ce6bc7e7b135 100644
> > --- a/drivers/gpu/drm/sti/sti_vtg.c
> > +++ b/drivers/gpu/drm/sti/sti_vtg.c
> > @@ -143,12 +143,17 @@ struct sti_vtg {
> >  struct sti_vtg *of_vtg_find(struct device_node *np)
> >  {
> >  	struct platform_device *pdev;
> > +	struct sti_vtg *vtg;
> >  
> >  	pdev = of_find_device_by_node(np);
> >  	if (!pdev)
> >  		return NULL;
> >  
> > -	return (struct sti_vtg *)platform_get_drvdata(pdev);
> > +	vtg = platform_get_drvdata(pdev);
> > +
> > +	put_device(&pdev->dev);
> 
> I would prefer of_node_put() instead, which does the same basically, but
> at least it is more obviously linked to of_find_device_by_node().

of_node_put() operates on OF nodes, but here it is the platform device
that is leaking.

> > +
> > +	return vtg;
> >  }

Johan