linux-kernel - Re: [PATCH v2] clk: Skip clk provider registration when np is NULL

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Date:   Mon, 26 Apr 2021 11:17:44 -0700
From:   Saravana Kannan <saravanak@...gle.com>
To:     Tudor Ambarus <tudor.ambarus@...rochip.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>, nsaenz@...nel.org,
        maxime@...no.tech, Kevin Hilman <khilman@...nel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        "Brown, Len" <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Marc Zyngier <maz@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Nicolas Saenz Julienne <nsaenzjulienne@...e.de>,
        Guenter Roeck <linux@...ck-us.net>,
        guillaume.tucker@...labora.com,
        linux-clk <linux-clk@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Jonathan Corbet <corbet@....net>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Claudiu Beznea <claudiu.beznea@...rochip.com>,
        Linux Doc Mailing List <linux-doc@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Android Kernel Team <kernel-team@...roid.com>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS <devicetre
        e@...r.kernel.org>, ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Android Kernel Team <kernel-team@...roid.com>, linux-rpi-kernel" 
        <linux-rpi-kernel@...ts.infradead.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>
Subject: Re: [PATCH v2] clk: Skip clk provider registration when np is NULL

On Sun, Apr 25, 2021 at 11:56 PM Tudor Ambarus
<tudor.ambarus@...rochip.com> wrote:
>
> commit 6579c8d97ad7 ("clk: Mark fwnodes when their clock provider is added")
> revealed that clk/bcm/clk-raspberrypi.c driver calls
> devm_of_clk_add_hw_provider(), with a NULL dev->of_node, which resulted in a
> NULL pointer dereference in of_clk_add_hw_provider() when calling
> fwnode_dev_initialized().
>
> Returning 0 is reducing the if conditions in driver code and is being
> consistent with the CONFIG_OF=n inline stub that returns 0 when CONFIG_OF
> is disabled. The downside is that drivers will maybe register clkdev lookups
> when they don't need to and waste some memory.
>
> Reported-by: Marek Szyprowski <m.szyprowski@...sung.com>
> Fixes: 6579c8d97ad7 ("clk: Mark fwnodes when their clock provider is added")
> Fixes: 3c9ea42802a1 ("clk: Mark fwnodes when their clock provider is added/removed")
> Signed-off-by: Tudor Ambarus <tudor.ambarus@...rochip.com>
> Reviewed-by: Stephen Boyd <sboyd@...nel.org>
> ---

Reviewed-by: Saravana Kannan <saravanak@...gle.com>

-Saravana

> v2:
> - s/return 0;/return; in void of_clk_del_provider()
> - add second fixes tag and Stephen's R-b tag
> The opinions on whether to return an error or zero were split. Returning 0
> and skipping the logic was considered safer as we don't know for sure if
> other drivers are affected. See:
> https://lore.kernel.org/lkml/d24bebc5-0f78-021f-293f-e58defa32531@samsung.com/
> https://lore.kernel.org/lkml/20210423171335.262316-1-tudor.ambarus@microchip.com/
>
>  drivers/clk/clk.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
>
> diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> index a3b30f7de2ef..b47460b40d14 100644
> --- a/drivers/clk/clk.c
> +++ b/drivers/clk/clk.c
> @@ -4552,6 +4552,9 @@ int of_clk_add_provider(struct device_node *np,
>         struct of_clk_provider *cp;
>         int ret;
>
> +       if (!np)
> +               return 0;
> +
>         cp = kzalloc(sizeof(*cp), GFP_KERNEL);
>         if (!cp)
>                 return -ENOMEM;
> @@ -4591,6 +4594,9 @@ int of_clk_add_hw_provider(struct device_node *np,
>         struct of_clk_provider *cp;
>         int ret;
>
> +       if (!np)
> +               return 0;
> +
>         cp = kzalloc(sizeof(*cp), GFP_KERNEL);
>         if (!cp)
>                 return -ENOMEM;
> @@ -4688,6 +4694,9 @@ void of_clk_del_provider(struct device_node *np)
>  {
>         struct of_clk_provider *cp;
>
> +       if (!np)
> +               return;
> +
>         mutex_lock(&of_clk_mutex);
>         list_for_each_entry(cp, &of_clk_providers, link) {
>                 if (cp->node == np) {
> --
> 2.25.1
>