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From:   Saravana Kannan <saravanak@google.com>
Date:   Fri, 14 May 2021 09:04:23 -0700
Message-ID: <CAGETcx87y-tpSaKRpugons1RZaPC-rdvdueUPuNFJHWDDyrNwQ@mail.gmail.com>
Subject: Re: [PATCH v1 2/2] drivers: base: Reduce device link removal code duplication
To:     "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        LKML <linux-kernel@vger.kernel.org>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        chenxiang <chenxiang66@hisilicon.com>
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On Fri, May 14, 2021 at 5:12 AM Rafael J. Wysocki <rjw@rjwysocki.net> wrote:
>
> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
>
> Reduce device link removal code duplication between the cases when
> SRCU is enabled and when it is disabled by moving the only differing
> piece of it (which is the removal of the link from the consumer and
> supplier lists) into a separate wrapper function (defined differently
> for each of the cases in question).
>
> No intentional functional impact.
>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> ---
>  drivers/base/core.c |   31 +++++++++++++------------------
>  1 file changed, 13 insertions(+), 18 deletions(-)
>
> Index: linux-pm/drivers/base/core.c
> ===================================================================
> --- linux-pm.orig/drivers/base/core.c
> +++ linux-pm/drivers/base/core.c
> @@ -198,6 +198,12 @@ static void device_link_synchronize_remo
>  {
>         synchronize_srcu(&device_links_srcu);
>  }
> +
> +static void device_link_remove_from_lists(struct device_link *link)
> +{
> +       list_del_rcu(&link->s_node);
> +       list_del_rcu(&link->c_node);
> +}
>  #else /* !CONFIG_SRCU */
>  static DECLARE_RWSEM(device_links_lock);
>
> @@ -232,6 +238,12 @@ int device_links_read_lock_held(void)
>  static inline void device_link_synchronize_removal(void)
>  {
>  }
> +
> +static void device_link_remove_from_lists(struct device_link *link)
> +{
> +       list_del(&link->s_node);
> +       list_del(&link->c_node);
> +}
>  #endif /* !CONFIG_SRCU */
>
>  static bool device_is_ancestor(struct device *dev, struct device *target)
> @@ -854,7 +866,6 @@ out:
>  }
>  EXPORT_SYMBOL_GPL(device_link_add);
>
> -#ifdef CONFIG_SRCU
>  static void __device_link_del(struct kref *kref)
>  {
>         struct device_link *link = container_of(kref, struct device_link, kref);
> @@ -864,25 +875,9 @@ static void __device_link_del(struct kre
>
>         pm_runtime_drop_link(link);
>
> -       list_del_rcu(&link->s_node);
> -       list_del_rcu(&link->c_node);
> +       device_link_remove_from_lists(link);

Remind me again why we can't do the synchronize_srcu() here (I'm not
too familiar with the SRCU API semantics)? Is it because
synchronize_srcu() can take indefinitely long? I just vaguely remember
it does some checks during CPUs going idle (which can be a long time
later) but I'm not sure if that's the earliest you can synchronize. If
it's not indefinitely long and we just need to wait for other SRCU
critical sections to exit, maybe we can just synchronize here and make
the code a lot simpler?

This function is anyway called in a sleepable context.


-Saravana

>         device_unregister(&link->link_dev);
>  }
> -#else /* !CONFIG_SRCU */
> -static void __device_link_del(struct kref *kref)
> -{
> -       struct device_link *link = container_of(kref, struct device_link, kref);
> -
> -       dev_info(link->consumer, "Dropping the link to %s\n",
> -                dev_name(link->supplier));
> -
> -       pm_runtime_drop_link(link);
> -
> -       list_del(&link->s_node);
> -       list_del(&link->c_node);
> -       device_unregister(&link->link_dev);
> -}
> -#endif /* !CONFIG_SRCU */
>
>  static void device_link_put_kref(struct device_link *link)
>  {
>
>
>