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

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Date:   Thu, 25 Mar 2021 16:00:07 +0000
From:   Changbin Du <changbin.du@...il.com>
To:     Rob Herring <robh+dt@...nel.org>
Cc:     Changbin Du <changbin.du@...il.com>,
        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 10:52:30AM -0600, Rob Herring wrote:
> 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?
>
This aligns to what unflatten_and_copy_device_tree() does.
 
> > +               return;
> 
> And the arch is supposed to just continue on oblivious that it has no DT?
>
As checking the arch code(arm, riscv), I suppose so.

> > +       }
> > +
> >         __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.
> 
No, we have returned before.

> >
> > --
> > 2.30.2
> >

-- 
Cheers,
Changbin Du