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From: Tony Lindgren <tony@atomide.com>
To: "Russell King (Oracle)" <linux@armlinux.org.uk>
Cc: Liang He <windhl@126.com>,
	andre.przywara@arm.com, thierry.reding@gmail.com,
	jonathanh@nvidia.com, linux-arm-kernel@lists.infradead.org,
	linux-omap@vger.kernel.org, linux-tegra@vger.kernel.org,
	Krzysztof Kozlowski <krzk@kernel.org>
Subject: Re: [PATCH] arm/mach: Hold reference returned by of_find_xxx APIs
Date: Wed, 29 Jun 2022 11:37:38 +0300	[thread overview]
Message-ID: <YrwPUgzXgDp5djxM@atomide.com> (raw)
In-Reply-To: <YrspRE+g7QvzOvgr@shell.armlinux.org.uk>

* Russell King (Oracle) <linux@armlinux.org.uk> [220628 16:11]:
> On Tue, Jun 28, 2022 at 06:59:45AM +0300, Tony Lindgren wrote:
> > * Liang He <windhl@126.com> [220621 12:14]:
> > > diff --git a/arch/arm/mach-omap2/pmic-cpcap.c b/arch/arm/mach-omap2/pmic-cpcap.c
> > > index 668dc84fd31e..a7368d657aa8 100644
> > > --- a/arch/arm/mach-omap2/pmic-cpcap.c
> > > +++ b/arch/arm/mach-omap2/pmic-cpcap.c
> > > @@ -238,8 +238,11 @@ static struct omap_voltdm_pmic omap4_fan_iva = {
> > >  int __init omap4_cpcap_init(void)
> > >  {
> > >  	struct voltagedomain *voltdm;
> > > +	struct device_node *np;
> > >  
> > > -	if (!of_find_compatible_node(NULL, NULL, "motorola,cpcap"))
> > > +	np = of_find_compatible_node(NULL, NULL, "motorola,cpcap");
> > > +	of_node_put(np);
> > > +	if (!np)
> > >  		return -ENODEV;
> > 
> > Hmm so here you are checking for !np after of_node_put()?
> 
> This is permissible, because the value of the _pointer_ is being
> checked without dereferencing the pointer. So the fact that the
> node may have been freed is actually immaterial.

OK yeah. This is several lines of code to check if something exists.
Maybe we should just add bool of_compatible_node_exists() to simplify
cases like this that does not keep the kfef.

Regards,

Tony

WARNING: multiple messages have this Message-ID (diff)
From: Tony Lindgren <tony@atomide.com>
To: "Russell King (Oracle)" <linux@armlinux.org.uk>
Cc: Liang He <windhl@126.com>,
	andre.przywara@arm.com, thierry.reding@gmail.com,
	jonathanh@nvidia.com, linux-arm-kernel@lists.infradead.org,
	linux-omap@vger.kernel.org, linux-tegra@vger.kernel.org,
	Krzysztof Kozlowski <krzk@kernel.org>
Subject: Re: [PATCH] arm/mach: Hold reference returned by of_find_xxx APIs
Date: Wed, 29 Jun 2022 11:37:38 +0300	[thread overview]
Message-ID: <YrwPUgzXgDp5djxM@atomide.com> (raw)
In-Reply-To: <YrspRE+g7QvzOvgr@shell.armlinux.org.uk>

* Russell King (Oracle) <linux@armlinux.org.uk> [220628 16:11]:
> On Tue, Jun 28, 2022 at 06:59:45AM +0300, Tony Lindgren wrote:
> > * Liang He <windhl@126.com> [220621 12:14]:
> > > diff --git a/arch/arm/mach-omap2/pmic-cpcap.c b/arch/arm/mach-omap2/pmic-cpcap.c
> > > index 668dc84fd31e..a7368d657aa8 100644
> > > --- a/arch/arm/mach-omap2/pmic-cpcap.c
> > > +++ b/arch/arm/mach-omap2/pmic-cpcap.c
> > > @@ -238,8 +238,11 @@ static struct omap_voltdm_pmic omap4_fan_iva = {
> > >  int __init omap4_cpcap_init(void)
> > >  {
> > >  	struct voltagedomain *voltdm;
> > > +	struct device_node *np;
> > >  
> > > -	if (!of_find_compatible_node(NULL, NULL, "motorola,cpcap"))
> > > +	np = of_find_compatible_node(NULL, NULL, "motorola,cpcap");
> > > +	of_node_put(np);
> > > +	if (!np)
> > >  		return -ENODEV;
> > 
> > Hmm so here you are checking for !np after of_node_put()?
> 
> This is permissible, because the value of the _pointer_ is being
> checked without dereferencing the pointer. So the fact that the
> node may have been freed is actually immaterial.

OK yeah. This is several lines of code to check if something exists.
Maybe we should just add bool of_compatible_node_exists() to simplify
cases like this that does not keep the kfef.

Regards,

Tony

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  reply	other threads:[~2022-06-29  8:37 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-06-21  9:19 [PATCH] arm/mach: Hold reference returned by of_find_xxx APIs Liang He
2022-06-21  9:19 ` Liang He
2022-06-22  8:51 ` Krzysztof Kozlowski
2022-06-22  8:51   ` Krzysztof Kozlowski
2022-06-28  3:59 ` Tony Lindgren
2022-06-28  3:59   ` Tony Lindgren
2022-06-28  4:05   ` Liang He
2022-06-28  4:05     ` Liang He
2022-06-28 16:16   ` Russell King (Oracle)
2022-06-28 16:16     ` Russell King (Oracle)
2022-06-29  8:37     ` Tony Lindgren [this message]
2022-06-29  8:37       ` Tony Lindgren

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