linux-kernel - Re: [PATCH v2 2/6] of: dynamic: Refactor action prints to not use "%pOF" inside devtree

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Message-ID: <CAMuHMdX4gqPLv5ZWiWe-B+bQtHSfF9AxZTKWisFZEKa29Ge2KQ@mail.gmail.com>
Date:   Fri, 18 Aug 2023 17:36:26 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Rob Herring <robh@...nel.org>
Cc:     Frank Rowand <frowand.list@...il.com>,
        "Enrico Weigelt, metux IT consult" <info@...ux.net>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Petr Mladek <pmladek@...e.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/6] of: dynamic: Refactor action prints to not use
 "%pOF" inside devtree_lock

Hi Rob,

On Sat, Aug 5, 2023 at 12:42 AM Rob Herring <robh@...nel.org> wrote:
> While originally it was fine to format strings using "%pOF" while
> holding devtree_lock, this now causes a deadlock.  Lockdep reports:
>
>     of_get_parent from of_fwnode_get_parent+0x18/0x24
>     ^^^^^^^^^^^^^
>     of_fwnode_get_parent from fwnode_count_parents+0xc/0x28
>     fwnode_count_parents from fwnode_full_name_string+0x18/0xac
>     fwnode_full_name_string from device_node_string+0x1a0/0x404
>     device_node_string from pointer+0x3c0/0x534
>     pointer from vsnprintf+0x248/0x36c
>     vsnprintf from vprintk_store+0x130/0x3b4
>
> Fix this by moving the printing in __of_changeset_entry_apply() outside
> the lock. As the only difference in the the multiple prints is the
> action name, use the existing "action_names" to refactor the prints into
> a single print.
>
> Fixes: a92eb7621b9fb2c2 ("lib/vsprintf: Make use of fwnode API to obtain node names and separators")
> Reported-by: Geert Uytterhoeven <geert+renesas@...der.be>
> Signed-off-by: Rob Herring <robh@...nel.org>
> ---
> v5 (v2 in this series):
>  - Move majority of refactoring to separate patch and minimize the fix
>    to just moving the print out of the locked section.

Thanks for your patch!

> --- a/drivers/of/dynamic.c
> +++ b/drivers/of/dynamic.c

> @@ -648,20 +634,17 @@ static int __of_changeset_entry_apply(struct of_changeset_entry *ce)
>                 }
>
>                 ret = __of_update_property(ce->np, ce->prop, &old_prop);
> -               if (ret) {
> -                       pr_err("changeset: update_property failed @%pOF/%s\n",
> -                               ce->np,
> -                               ce->prop->name);
> -                       break;
> -               }
>                 break;
>         default:
>                 ret = -EINVAL;
>         }
>         raw_spin_unlock_irqrestore(&devtree_lock, flags);
>
> -       if (ret)
> +       if (ret) {
> +               pr_err("changeset: apply failed: cset<%p> %-15s %pOF:%s\n",

Printing the cset pointer will (needlessly?) complicate the EXPECT_*()
handling in the unit test.

> +                      ce, action_names[ce->action], ce->np, ce->prop->name);

This should check ce->action to avoid an out-of-bounds access beyond
the end of action_names[].

>                 return ret;
> +       }
>
>         switch (ce->action) {
>         case OF_RECONFIG_ATTACH_NODE:

The rest LGTM to me.

Gr{oetje,eeting}s,

                        Geert

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