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

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Message-ID: <CAL_Jsq+2nz9MCLffKEHxygUbMNisNAFh_i-8BaZjXy_eDHEi0g@mail.gmail.com>
Date:   Fri, 18 Aug 2023 11:16:53 -0500
From:   Rob Herring <robh@...nel.org>
To:     Geert Uytterhoeven <geert@...ux-m68k.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

On Fri, Aug 18, 2023 at 10:36 AM Geert Uytterhoeven
<geert@...ux-m68k.org> wrote:
>
> 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.

That's added largely because the other prints which I rework later in
this series had them. Either printing the changeset ptr is useful or
it isn't. I think people running the unittest and the post-processor
can easily enough filter this out when looking at the results.
Honestly, even I probably run it less than once a cycle.

>
> > +                      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[].

Indeed.

I think I'll add "invalid" to action_names names and then do something
like: "(ce->action < FOO) ? ce->action : 0".

Rob