linux-kernel - Re: [PATCH v4] irqchip/renesas-rzg2l: Fix missing put

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Message-ID: <CAMuHMdWYZizs_3Q6mEXCfaivmSy7CYEj1uvHVrA7=9NM+9Ov1w@mail.gmail.com>
Date: Tue, 11 Feb 2025 17:16:25 +0100
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Fabrizio Castro <fabrizio.castro.jz@...esas.com>
Cc: Thomas Gleixner <tglx@...utronix.de>, Markus Elfring <elfring@...rs.sourceforge.net>, 
	Markus Elfring <Markus.Elfring@....de>, Marc Zyngier <maz@...nel.org>, 
	Prabhakar Mahadev Lad <prabhakar.mahadev-lad.rj@...renesas.com>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Chris Paterson <Chris.Paterson2@...esas.com>, 
	Biju Das <biju.das.jz@...renesas.com>, 
	"linux-renesas-soc@...r.kernel.org" <linux-renesas-soc@...r.kernel.org>, Dan Williams <dan.j.williams@...el.com>, 
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v4] irqchip/renesas-rzg2l: Fix missing put_device

Hi Fabrizio,

On Tue, 11 Feb 2025 at 16:49, Fabrizio Castro
<fabrizio.castro.jz@...esas.com> wrote:
> > From: Geert Uytterhoeven <geert@...ux-m68k.org>
> > Sent: 11 February 2025 15:12
> > Subject: Re: [PATCH v4] irqchip/renesas-rzg2l: Fix missing put_device
> >
> > On Fri, 11 Oct 2024 at 19:20, Fabrizio Castro
> > <fabrizio.castro.jz@...esas.com> wrote:
> > > rzg2l_irqc_common_init calls of_find_device_by_node, but the
> > > corresponding put_device call is missing.
> > > This also gets reported by make coccicheck.
> > >
> > > Make use of the cleanup interfaces from cleanup.h to call into
> > > __free_put_device (which in turn calls into put_device) when
> > > leaving function rzg2l_irqc_common_init and variable "dev" goes
> > > out of scope.
> > >
> > > Mind that we don't want to "put" "dev" when rzg2l_irqc_common_init
> > > completes successfully, therefore assign NULL to "dev" to prevent
> > > __free_put_device from calling into put_device within the successful
> > > path.
> > >
> > > "make coccicheck" will still complain about missing put_device calls,
> > > but those are false positives now.
> > >
> > > Fixes: 3fed09559cd8 ("irqchip: Add RZ/G2L IA55 Interrupt Controller driver")
> > > Signed-off-by: Fabrizio Castro <fabrizio.castro.jz@...esas.com>
> >
> > Revisiting commit d038109ac1c6bf61 ("irqchip/renesas-rzg2l: Fix missing
> > put_device")...
> >
> > > --- a/drivers/irqchip/irq-renesas-rzg2l.c
> > > +++ b/drivers/irqchip/irq-renesas-rzg2l.c
> > > @@ -8,6 +8,7 @@
> > >   */
> > >
> > >  #include <linux/bitfield.h>
> > > +#include <linux/cleanup.h>
> > >  #include <linux/clk.h>
> > >  #include <linux/err.h>
> > >  #include <linux/io.h>
> > > @@ -530,12 +531,12 @@ static int rzg2l_irqc_parse_interrupts(struct rzg2l_irqc_priv *priv,
> > >  static int rzg2l_irqc_common_init(struct device_node *node, struct device_node *parent,
> > >                                   const struct irq_chip *irq_chip)
> > >  {
> > > +       struct platform_device *pdev = of_find_device_by_node(node);
> > > +       struct device *dev __free(put_device) = pdev ? &pdev->dev : NULL;
> >
> > Now there is a variable holding "&pdev->dev", all below references
> > to the latter can be replaced by "dev"...
>
> Right! I will shortly send a patch for this.

Thanks in advance!

> > >         struct irq_domain *irq_domain, *parent_domain;
> > > -       struct platform_device *pdev;
> > >         struct reset_control *resetn;
> > >         int ret;
> > >
> > > -       pdev = of_find_device_by_node(node);
> > >         if (!pdev)
> > >                 return -ENODEV;
> > >
> > > @@ -591,6 +592,17 @@ static int rzg2l_irqc_common_init(struct device_node *node, struct device_node
> > *
> > >
> > >         register_syscore_ops(&rzg2l_irqc_syscore_ops);
> > >
> > > +       /*
> > > +        * Prevent the cleanup function from invoking put_device by assigning
> > > +        * NULL to dev.
> > > +        *
> > > +        * make coccicheck will complain about missing put_device calls, but
> > > +        * those are false positives, as dev will be automatically "put" via
> > > +        * __free_put_device on the failing path.
> > > +        * On the successful path we don't actually want to "put" dev.
> > > +        */
> > > +       dev = NULL;
> > > +
> > >         return 0;
> >
> > Can't the above be replaced by
> >
> >     no_free_ptr(dev);
> >
> > ? Or would Coccinelle still complain?
>
> If I use no_free_ptr the compiler complains that its return value is not used:
>
> In file included from ../drivers/irqchip/irq-renesas-rzg2l.c:11:
> ../drivers/irqchip/irq-renesas-rzg2l.c: In function ‘rzg2l_irqc_common_init’:
> ../include/linux/cleanup.h:215:15: warning: ignoring return value of ‘__must_check_fn’ declared with attribute ‘warn_unused_result’ [-Wunused-result]
>   215 |  ((typeof(p)) __must_check_fn(__get_and_null(p, NULL)))
>       |               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> ../drivers/irqchip/irq-renesas-rzg2l.c:595:2: note: in expansion of macro ‘no_free_ptr’
>   595 |  no_free_ptr(dev);
>       |  ^~~~~~~~~~~

I hadn't tried it myself, and thus hadn't noticed that warning.
Interestingly, the addition of __must_check_fn()[1] predates the
documentation[2] that shows the above construct...

[1] commit 85be6d842447067c ("cleanup: Make no_free_ptr() __must_check"),
[2] commit d5934e76316e84ec ("cleanup: Add usage and style documentation").

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds