Re: [PATCH] driver core: bus: move lock_class_key into dynamic structure

[Rafael J. Wysocki]

On Wed, Feb 1, 2023 at 9:33 AM Greg Kroah-Hartman
<gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
>
> Move the lock_class_key structure out of struct bus_type and into the
> dynamic structure we create already for all bus_types registered with
> the kernel.  This saves on static space and removes one more writable
> field in struct bus_type.
>
> In the future, the same field can be moved out of the struct class logic
> because it shares this same private structure.
>
> Most everyone will never notice this change, as lockdep is not enabled
> in real systems so no memory or logic changes are happening for them.
>
> Cc: "Rafael J. Wysocki" <rafael@xxxxxxxxxx>
> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

This looks reasonable to me, so

Acked-by: Rafael J. Wysocki <rafael@xxxxxxxxxx>

> ---
>  drivers/base/base.h        | 2 ++
>  drivers/base/bus.c         | 5 ++++-
>  include/linux/device/bus.h | 1 -
>  3 files changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/base/base.h b/drivers/base/base.h
> index 2208af509ce8..0e806f641079 100644
> --- a/drivers/base/base.h
> +++ b/drivers/base/base.h
> @@ -52,6 +52,8 @@ struct subsys_private {
>
>         struct kset glue_dirs;
>         struct class *class;
> +
> +       struct lock_class_key lock_key;
>  };
>  #define to_subsys_private(obj) container_of_const(obj, struct subsys_private, subsys.kobj)
>
> diff --git a/drivers/base/bus.c b/drivers/base/bus.c
> index cf1b8f00b4c0..aa70b3a7d778 100644
> --- a/drivers/base/bus.c
> +++ b/drivers/base/bus.c
> @@ -154,6 +154,7 @@ static void bus_release(struct kobject *kobj)
>         struct subsys_private *priv = to_subsys_private(kobj);
>         struct bus_type *bus = priv->bus;
>
> +       lockdep_unregister_key(&priv->lock_key);
>         kfree(priv);
>         bus->p = NULL;
>  }
> @@ -743,7 +744,7 @@ int bus_register(struct bus_type *bus)
>  {
>         int retval;
>         struct subsys_private *priv;
> -       struct lock_class_key *key = &bus->lock_key;
> +       struct lock_class_key *key;
>
>         priv = kzalloc(sizeof(struct subsys_private), GFP_KERNEL);
>         if (!priv)
> @@ -785,6 +786,8 @@ int bus_register(struct bus_type *bus)
>         }
>
>         INIT_LIST_HEAD(&priv->interfaces);
> +       key = &priv->lock_key;
> +       lockdep_register_key(key);
>         __mutex_init(&priv->mutex, "subsys mutex", key);
>         klist_init(&priv->klist_devices, klist_devices_get, klist_devices_put);
>         klist_init(&priv->klist_drivers, NULL, NULL);
> diff --git a/include/linux/device/bus.h b/include/linux/device/bus.h
> index 87e4d029c915..e3094db1e9fa 100644
> --- a/include/linux/device/bus.h
> +++ b/include/linux/device/bus.h
> @@ -112,7 +112,6 @@ struct bus_type {
>         const struct iommu_ops *iommu_ops;
>
>         struct subsys_private *p;
> -       struct lock_class_key lock_key;
>
>         bool need_parent_lock;
>  };
> --
> 2.39.1
>