Re: [PATCH 1/3] driver core: Support asynchronous driver shutdown

[Sagi Grimberg <sagi@grimberg.me>]

> From: Tanjore Suresh <tansuresh@google.com>
> 
> This changes the bus driver interface with additional entry points
> to enable devices to implement asynchronous shutdown. The existing
> synchronous interface to shutdown is unmodified and retained for
> backward compatibility.
> 
> This changes the common device shutdown code to enable devices to
> participate in asynchronous shutdown implementation.
> 
> Signed-off-by: Tanjore Suresh <tansuresh@google.com>
> ---
>   drivers/base/core.c        | 39 +++++++++++++++++++++++++++++++++++++-
>   include/linux/device/bus.h | 10 ++++++++++
>   2 files changed, 48 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/base/core.c b/drivers/base/core.c
> index 67ba592afc77..d9745822fb50 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(async_shutdown_list);
>   
>   	wait_for_device_probe();
>   	device_block_probing();
> @@ -4769,7 +4770,14 @@ void device_shutdown(void)
>   				dev_info(dev, "shutdown_pre\n");
>   			dev->class->shutdown_pre(dev);
>   		}
> -		if (dev->bus && dev->bus->shutdown) {
> +
> +		if (dev->bus && dev->bus->shutdown_pre) {

I'm assuming that there is no shutdown_pre without a shutdown_post
paired with it, so I think the code should verify that.

> +			if (initcall_debug)
> +				dev_info(dev, "shutdown_pre\n");
> +			dev->bus->shutdown_pre(dev);
> +			list_add(&dev->kobj.entry,
> +				&async_shutdown_list);
> +		} else if (dev->bus && dev->bus->shutdown) {
>   			if (initcall_debug)
>   				dev_info(dev, "shutdown\n");
>   			dev->bus->shutdown(dev);
> @@ -4789,6 +4797,35 @@ void device_shutdown(void)
>   		spin_lock(&devices_kset->list_lock);
>   	}
>   	spin_unlock(&devices_kset->list_lock);
> +
> +	/*
> +	 * Second pass spin for only devices, that have configured
> +	 * Asynchronous shutdown.
> +	 */
> +	while (!list_empty(&async_shutdown_list)) {
> +		dev = list_entry(async_shutdown_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 (dev->bus && dev->bus->shutdown_post) {
> +			if (initcall_debug)
> +				dev_info(dev,
> +				"shutdown_post called\n");
> +			dev->bus->shutdown_post(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 ae10c4322754..cbcb001f6336 100644
> --- a/include/linux/device/bus.h
> +++ b/include/linux/device/bus.h
> @@ -48,6 +48,14 @@ 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_pre:	Called at the shutdown-time to start the shutdown
> + *			process on the device. This entry point will be called
> + *			only when the bus driver has indicated it would like
> + *			to participate in asynchronous shutdown completion.
> + * @shutdown_post:	Called at shutdown-time  to complete the shutdown
> + *			process of the device. This entry point will be called
> + *			only when the bus drive has indicated it would like to
> + *			participate in the asynchronous shutdown completion.
>    *
>    * @online:	Called to put the device back online (after offlining it).
>    * @offline:	Called to put the device offline for hot-removal. May fail.
> @@ -90,6 +98,8 @@ struct bus_type {
>   	void (*sync_state)(struct device *dev);
>   	void (*remove)(struct device *dev);
>   	void (*shutdown)(struct device *dev);
> +	void (*shutdown_pre)(struct device *dev);
> +	void (*shutdown_post)(struct device *dev);
>   
>   	int (*online)(struct device *dev);
>   	int (*offline)(struct device *dev);