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References: <20230301185209.274134-1-jjhiblot@traphandler.com> <20230301185209.274134-3-jjhiblot@traphandler.com>
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From:   Geert Uytterhoeven <geert@linux-m68k.org>
Date:   Thu, 2 Mar 2023 08:49:44 +0100
Message-ID: <CAMuHMdVF337k+zyjpbzoDtWWDnYhM6eM3+As6UuZ7FCgASsMQg@mail.gmail.com>
Subject: Re: [PATCH 2/3] of: irq: make callers of of_irq_parse_one() release
 the device node
To:     Jean-Jacques Hiblot <jjhiblot@traphandler.com>
Cc:     saravanak@google.com, clement.leger@bootlin.com,
        Magnus Damm <magnus.damm@gmail.com>,
        Russell King <linux@armlinux.org.uk>,
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        Christophe Leroy <christophe.leroy@csgroup.eu>,
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        Thomas Gleixner <tglx@linutronix.de>,
        Claudiu Beznea <claudiu.beznea@microchip.com>,
        Marc Zyngier <maz@kernel.org>, afaerber@suse.de,
        Manivannan Sadhasivam <mani@kernel.org>,
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        Chen-Yu Tsai <wens@csie.org>,
        Jernej Skrabec <jernej.skrabec@gmail.com>,
        Samuel Holland <samuel@sholland.org>,
        Rob Herring <robh+dt@kernel.org>,
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Hi Jean-Jacques,

Thanks for your patch!

On Wed, Mar 1, 2023 at 7:53 PM Jean-Jacques Hiblot
<jjhiblot@traphandler.com> wrote:
> of_irq_parse_one() does a get() on the device node returned in out_irq->np.
> Callers of of_irq_parse_one() must do a put() when they are done with it.

What does "be done with it" really mean here?

> Signed-off-by: Jean-Jacques Hiblot <jjhiblot@traphandler.com>

> --- a/arch/arm/mach-shmobile/regulator-quirk-rcar-gen2.c
> +++ b/arch/arm/mach-shmobile/regulator-quirk-rcar-gen2.c
> @@ -184,6 +184,7 @@ static int __init rcar_gen2_regulator_quirk(void)
>                         kfree(quirk);
>                         continue;
>                 }
> +               of_node_put(argsa->np);

The quirk object, which is a container of argsa, is still used below,
and stored in a linked list.  I agree argsa->np is not dereferenced,
but the pointer itself is still compared to other pointers.
IIUIC, calling of_node_put() might cause the reference count to drop to
zero, and the underlying struct node object to be deallocated.
So when a future reference to the same DT node will be taken, a new
struct node object will be allocated, and the pointer comparison below
will fail?

Or am I missing something?

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-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