linux-kernel - Re: [PATCH 2/3] of: irq: make callers of of_irq_parse

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Date:   Sat, 4 Mar 2023 11:34:39 +0100
From:   Jean-Jacques Hiblot <jjhiblot@...phandler.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
CC:     <saravanak@...gle.com>, <clement.leger@...tlin.com>,
        Magnus Damm <magnus.damm@...il.com>,
        Russell King <linux@...linux.org.uk>,
        Michael Ellerman <mpe@...erman.id.au>,
        Nicholas Piggin <npiggin@...il.com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        <zajec5@...il.com>, Daniel Lezcano <daniel.lezcano@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Claudiu Beznea <claudiu.beznea@...rochip.com>,
        Marc Zyngier <maz@...nel.org>, <afaerber@...e.de>,
        Manivannan Sadhasivam <mani@...nel.org>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Chen-Yu Tsai <wens@...e.org>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Samuel Holland <samuel@...lland.org>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Nishanth Menon <nm@...com>, <ssantosh@...nel.org>,
        <mathias.nyman@...el.com>, <gregkh@...uxfoundation.org>,
        <thierry.reding@...il.com>, <jonathanh@...dia.com>,
        <linux-renesas-soc@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <linuxppc-dev@...ts.ozlabs.org>,
        <linux-wireless@...r.kernel.org>,
        <linux-actions@...ts.infradead.org>,
        <linux-riscv@...ts.infradead.org>, <linux-sunxi@...ts.linux.dev>,
        <devicetree@...r.kernel.org>, <linux-pci@...r.kernel.org>,
        <linux-usb@...r.kernel.org>, <linux-tegra@...r.kernel.org>
Subject: Re: [PATCH 2/3] of: irq: make callers of of_irq_parse_one() release
 the device node



On 02/03/2023 08:49, Geert Uytterhoeven wrote:
> Hi Jean-Jacques,
> 
> Thanks for your patch!
> 
> On Wed, Mar 1, 2023 at 7:53 PM Jean-Jacques Hiblot
> <jjhiblot@...phandler.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@...phandler.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.
Hi Geert,

I fail to see when the pointers are compared. It looks to me that only 
the args are compared. Am I missing something ?
In any case, looking more closely at the code, I guess that indeed the
of_node_put() shouldn't be added here because this code expects that the
nodes never go away. That is probably a good assertion in case of PMICs

JJ
> 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
>