Re: [driver-core PATCH v5 5/9] driver core: Establish clear order of operations for deferred probe and remove

[Bart Van Assche <bvanassche-HInyCGIudOg@public.gmane.org>]

On Mon, 2018-11-05 at 13:12 -0800, Alexander Duyck wrote:
> One change I made in addition is I replaced the use of "bool X:1" to define
> the bitfield to a "u8 X:1" setup in order to resolve some checkpatch
> warnings.

Please use "bool X:1" instead of "u8 X:1". I think it was a bad idea to make
checkpatch complain about "bool X:1" since "bool X:1" should only be avoided
in structures for which alignment must be architecture-independent. For struct
device it is fine if member alignment differs per architecture. Additionally,
changing "bool X:1" into "u8 X:1" will reduce performance on architectures that
cannot do byte addressing.

>  static void __device_release_driver(struct device *dev, struct device *parent)
>  {
> -	struct device_driver *drv;
> +	struct device_driver *drv = dev->driver;
>  
> -	drv = dev->driver;
> -	if (drv) {
> -		while (device_links_busy(dev)) {
> -			__device_driver_unlock(dev, parent);
> +	/*
> +	 * In the event that we are asked to release the driver on an
> +	 * interface that is still waiting on a probe we can just terminate
> +	 * the probe by setting async_probe to false. When the async call
> +	 * is finally completed it will see this state and just exit.
> +	 */
> +	dev->async_probe = false;
> +	if (!drv)
> +		return;
>  
> -			device_links_unbind_consumers(dev);
> +	while (device_links_busy(dev)) {
> +		__device_driver_unlock(dev, parent);
>  
> -			__device_driver_lock(dev, parent);
> -			/*
> -			 * A concurrent invocation of the same function might
> -			 * have released the driver successfully while this one
> -			 * was waiting, so check for that.
> -			 */
> -			if (dev->driver != drv)
> -				return;
> -		}
> +		device_links_unbind_consumers(dev);
>  
> -		pm_runtime_get_sync(dev);
> -		pm_runtime_clean_up_links(dev);
> +		__device_driver_lock(dev, parent);
> +		/*
> +		 * A concurrent invocation of the same function might
> +		 * have released the driver successfully while this one
> +		 * was waiting, so check for that.
> +		 */
> +		if (dev->driver != drv)
> +			return;
> +	}
>  
> -		driver_sysfs_remove(dev);
> +	pm_runtime_get_sync(dev);
> +	pm_runtime_clean_up_links(dev);
>  
> -		if (dev->bus)
> -			blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
> -						     BUS_NOTIFY_UNBIND_DRIVER,
> -						     dev);
> +	driver_sysfs_remove(dev);
>  
> -		pm_runtime_put_sync(dev);
> +	if (dev->bus)
> +		blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
> +					     BUS_NOTIFY_UNBIND_DRIVER,
> +					     dev);
>  
> -		if (dev->bus && dev->bus->remove)
> -			dev->bus->remove(dev);
> -		else if (drv->remove)
> -			drv->remove(dev);
> +	pm_runtime_put_sync(dev);
>  
> -		device_links_driver_cleanup(dev);
> -		arch_teardown_dma_ops(dev);
> +	if (dev->bus && dev->bus->remove)
> +		dev->bus->remove(dev);
> +	else if (drv->remove)
> +		drv->remove(dev);
>  
> -		devres_release_all(dev);
> -		dev->driver = NULL;
> -		dev_set_drvdata(dev, NULL);
> -		if (dev->pm_domain && dev->pm_domain->dismiss)
> -			dev->pm_domain->dismiss(dev);
> -		pm_runtime_reinit(dev);
> -		dev_pm_set_driver_flags(dev, 0);
> +	device_links_driver_cleanup(dev);
> +	arch_teardown_dma_ops(dev);
> +
> +	devres_release_all(dev);
> +	dev->driver = NULL;
> +	dev_set_drvdata(dev, NULL);
> +	if (dev->pm_domain && dev->pm_domain->dismiss)
> +		dev->pm_domain->dismiss(dev);
> +	pm_runtime_reinit(dev);
> +	dev_pm_set_driver_flags(dev, 0);
>  
> -		klist_remove(&dev->p->knode_driver);
> -		device_pm_check_callbacks(dev);
> -		if (dev->bus)
> -			blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
> -						     BUS_NOTIFY_UNBOUND_DRIVER,
> -						     dev);
> +	klist_remove(&dev->p->knode_driver);
> +	device_pm_check_callbacks(dev);
> +	if (dev->bus)
> +		blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
> +					     BUS_NOTIFY_UNBOUND_DRIVER,
> +					     dev);
>  
> -		kobject_uevent(&dev->kobj, KOBJ_UNBIND);
> -	}
> +	kobject_uevent(&dev->kobj, KOBJ_UNBIND);
>  }

This patch mixes functional changes with whitespace changes. Please move the
whitespace changes into a separate patch such that this patch becomes easier
to read.
 
>  void device_release_driver_internal(struct device *dev,
> diff --git a/include/linux/device.h b/include/linux/device.h
> index 1b25c7a43f4c..fc7091d436c2 100644
> --- a/include/linux/device.h
> +++ b/include/linux/device.h
> @@ -1043,14 +1043,15 @@ struct device {
>  	struct iommu_group	*iommu_group;
>  	struct iommu_fwspec	*iommu_fwspec;
>  
> -	bool			offline_disabled:1;
> -	bool			offline:1;
> -	bool			of_node_reused:1;
> +	u8			offline_disabled:1;
> +	u8			offline:1;
> +	u8			of_node_reused:1;
>  #if defined(CONFIG_ARCH_HAS_SYNC_DMA_FOR_DEVICE) || \
>      defined(CONFIG_ARCH_HAS_SYNC_DMA_FOR_CPU) || \
>      defined(CONFIG_ARCH_HAS_SYNC_DMA_FOR_CPU_ALL)
> -	bool			dma_coherent:1;
> +	u8			dma_coherent:1;
>  #endif
> +	u8			async_probe:1;

The new async_probe field can be changed from multiple threads. Concurrent
changes of a bitfield are only safe if these are serialized in some way.
Please document the locking requirements for the async_probe bitfield in
device.h.

Thanks,

Bart.