Re: [PATCH] pmdomain: renesas: r8a78000: Fix lockdep false positive

[Ulf Hansson]

On Mon, Sep 7, 2026 at 4:32 PM Geert Uytterhoeven
<geert+renesas@xxxxxxxxx> wrote:
>
> Lockdep reports a possible circular locking dependency when attaching
> devices to an MDLC PM domain:
>
>   - During creation of the singleton PM domain:
>       A. r8a78000_genpd_always_on_singleton() takes r8a78000_mdlc_lock,
>       B. pm_genpd_init() takes gpd_list_lock.
>
>   - During attachment of devices to PM domains:
>       A. pm_genpd_add_device() takes gpd_list_lock,
>       B. r8a78000_mdlc_attach_dev() takes r8a78000_mdlc_lock.
>
> As the former is done only once, before any devices are attached, such a
> AB-BA deadlock cannot really happen.  Fix this false positive by
> introducing a separate lock to protect the creation of the singleton
> domain.
>
> Fixes: 89e6a71b35703f10 ("pmdomain: renesas: Add R-Car X5H MDLC driver")
> Signed-off-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>

Applied for next, thanks!

Kind regards
Uffe


> ---
>  drivers/pmdomain/renesas/r8a78000-mdlc.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/pmdomain/renesas/r8a78000-mdlc.c b/drivers/pmdomain/renesas/r8a78000-mdlc.c
> index 2668fc2ac9cbd388..1fd71bb3da776eb1 100644
> --- a/drivers/pmdomain/renesas/r8a78000-mdlc.c
> +++ b/drivers/pmdomain/renesas/r8a78000-mdlc.c
> @@ -45,8 +45,9 @@ struct r8a78000_mdlc_priv {
>  };
>
>  static struct generic_pm_domain *r8a78000_genpd_always_on;
> +
>  static HLIST_HEAD(r8a78000_mdlc_list);
> -static DEFINE_MUTEX(r8a78000_mdlc_lock);       /* protects the two above */
> +static DEFINE_MUTEX(r8a78000_mdlc_lock);       /* protects the list above */
>
>  static struct generic_pm_domain *r8a78000_genpd_xlate(
>                         const struct of_phandle_args *spec, void *data)
> @@ -191,10 +192,11 @@ static void r8a78000_genpd_del_provider(void *data)
>
>  static int r8a78000_genpd_always_on_singleton(struct device *dev)
>  {
> +       static DEFINE_MUTEX(singleton_lock);
>         struct generic_pm_domain *genpd;
>         int ret;
>
> -       guard(mutex)(&r8a78000_mdlc_lock);
> +       guard(mutex)(&singleton_lock);
>
>         if (r8a78000_genpd_always_on)
>                 return 0;
> --
> 2.43.0
>