[PATCH 1/5] driver core: Support two-pass driver shutdown.

[Saravana Kannan]

On Mon, Jan 29, 2024 at 10:19 AM Jeremy Allison <jallison at ciq.com> wrote:
>
> From: Tanjore Suresh <tansuresh at google.com>
>
> This changes the bus driver interface with an additional entry point
> to enable devices to implement two-pass shutdown. The existing
> synchronous interface to shutdown is called, and if a shutdown_wait
> method is defined the device is moved to an alternate list.

This sounds more like you need a parallelized async shutdown than a
two-pass shutdown. Similar to how async probes are done today. Why not
do that so it'll actually be useful in a more general fashion? You can
even add a flag like we have for probes so that drivers don't need to
do anything special to allow this parallelism.

-Saravana

>
> Once the shutdown method is called for all devices, the
> shutdown_wait method is then called synchronously for
> all devices on the alternate list.
>
> Signed-off-by: Tanjore Suresh <tansuresh at google.com>
> Signed-off-by: Jeremy Allison <jallison at ciq.com>
> ---
>  drivers/base/core.c        | 35 +++++++++++++++++++++++++++++++++++
>  include/linux/device/bus.h |  6 +++++-
>  2 files changed, 40 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/base/core.c b/drivers/base/core.c
> index 14d46af40f9a..c8b0d4c9abed 100644
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -4725,6 +4725,7 @@ EXPORT_SYMBOL_GPL(device_change_owner);
>  void device_shutdown(void)
>  {
>         struct device *dev, *parent;
> +       LIST_HEAD(shutdown_wait_list);
>
>         wait_for_device_probe();
>         device_block_probing();
> @@ -4769,10 +4770,17 @@ void device_shutdown(void)
>                                 dev_info(dev, "shutdown_pre\n");
>                         dev->class->shutdown_pre(dev);
>                 }
> +
>                 if (dev->bus && dev->bus->shutdown) {
>                         if (initcall_debug)
>                                 dev_info(dev, "shutdown\n");
>                         dev->bus->shutdown(dev);
> +                       /*
> +                        * Only put the device on the shutdown_wait_list
> +                        * if a shutdown_wait() method is also defined.
> +                        */
> +                       if (dev->bus->shutdown_wait)
> +                               list_add(&dev->kobj.entry, &shutdown_wait_list);
>                 } else if (dev->driver && dev->driver->shutdown) {
>                         if (initcall_debug)
>                                 dev_info(dev, "shutdown\n");
> @@ -4789,6 +4797,33 @@ void device_shutdown(void)
>                 spin_lock(&devices_kset->list_lock);
>         }
>         spin_unlock(&devices_kset->list_lock);
> +
> +       /*
> +        * Second pass only for devices that have configured
> +        * a shutdown_wait() method.
> +        */
> +       while (!list_empty(&shutdown_wait_list)) {
> +               dev = list_entry(shutdown_wait_list.next, struct device,
> +                               kobj.entry);
> +               parent = get_device(dev->parent);
> +               get_device(dev);
> +               /*
> +                * Make sure the device is off the  list
> +                */
> +               list_del_init(&dev->kobj.entry);
> +               if (parent)
> +                       device_lock(parent);
> +               device_lock(dev);
> +               if (initcall_debug)
> +                       dev_info(dev,
> +                       "shutdown_wait called\n");
> +               dev->bus->shutdown_wait(dev);
> +               device_unlock(dev);
> +               if (parent)
> +                       device_unlock(parent);
> +               put_device(dev);
> +               put_device(parent);
> +       }
>  }
>
>  /*
> diff --git a/include/linux/device/bus.h b/include/linux/device/bus.h
> index 5ef4ec1c36c3..a4132c44dac3 100644
> --- a/include/linux/device/bus.h
> +++ b/include/linux/device/bus.h
> @@ -48,7 +48,10 @@ struct fwnode_handle;
>   *             will never get called until they do.
>   * @remove:    Called when a device removed from this bus.
>   * @shutdown:  Called at shut-down time to quiesce the device.
> - *
> + * @shutdown_wait:     If this method exists, devices are stored on a separate
> + *                     list after shutdown() has been called and
> + *                     shutdown_wait() is called synchronously on each device
> + *                     in this list in turn.
>   * @online:    Called to put the device back online (after offlining it).
>   * @offline:   Called to put the device offline for hot-removal. May fail.
>   *
> @@ -87,6 +90,7 @@ struct bus_type {
>         void (*sync_state)(struct device *dev);
>         void (*remove)(struct device *dev);
>         void (*shutdown)(struct device *dev);
> +       void (*shutdown_wait)(struct device *dev);
>
>         int (*online)(struct device *dev);
>         int (*offline)(struct device *dev);
> --
> 2.39.3
>
>
>