linux-kernel - Re: [PATCH] of/fdt: Check dtb pointer first in unflatten_device

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Date:   Wed, 24 Mar 2021 10:52:30 -0600
From:   Rob Herring <robh+dt@...nel.org>
To:     Changbin Du <changbin.du@...il.com>
Cc:     Frank Rowand <frowand.list@...il.com>, devicetree@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] of/fdt: Check dtb pointer first in unflatten_device_tree

On Wed, Mar 24, 2021 at 9:04 AM Changbin Du <changbin.du@...il.com> wrote:
>
> The setup_arch() would invoke unflatten_device_tree() even no
> valid fdt found. So we'd better check it first and return early.
>
> Signed-off-by: Changbin Du <changbin.du@...il.com>
> ---
>  drivers/of/fdt.c | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
> index dcc1dd96911a..05d439d63bc5 100644
> --- a/drivers/of/fdt.c
> +++ b/drivers/of/fdt.c
> @@ -1225,6 +1225,11 @@ bool __init early_init_dt_scan(void *params)
>   */
>  void __init unflatten_device_tree(void)
>  {
> +       if (!initial_boot_params) {
> +               pr_warn("No valid device tree found, continuing without\n");

How are you going to see this message if you have no DT?

> +               return;

And the arch is supposed to just continue on oblivious that it has no DT?

> +       }
> +
>         __unflatten_device_tree(initial_boot_params, NULL, &of_root,
>                                 early_init_dt_alloc_memory_arch, false);

Soon as you get here with a NULL initial_boot_params, you'll get a
backtrace and halt.

>
> --
> 2.30.2
>