Re: [driver-core PATCH v7 3/9] device core: Consolidate locking and unlocking of parent and device

[Luis Chamberlain]

On Wed, Nov 28, 2018 at 04:32:21PM -0800, Alexander Duyck wrote:
> Try to consolidate all of the locking and unlocking of both the parent and
> device when attaching or removing a driver from a given device.
> 
> To do that I first consolidated the lock pattern into two functions
> __device_driver_lock and __device_driver_unlock. After doing that I then
> created functions specific to attaching and detaching the driver while
> acquiring these locks. By doing this I was able to reduce the number of
> spots where we touch need_parent_lock from 12 down to 4.

While this later is true, it gives the impression there are functional
changes but I see none. It can help reviewers / future reviewers of this
commit if its clearly stated that this patch introduces no functional
changes.

> Reviewed-by: Bart Van Assche <bvanassche@xxxxxxx>
> Reviewed-by: Dan Williams <dan.j.williams@xxxxxxxxx>
> Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> Signed-off-by: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx>

Reviewed-by: Luis Chamberlain <mcgrof@xxxxxxxxxx>

  Luis
> ---
>  drivers/base/base.h |    2 +
>  drivers/base/bus.c  |   23 ++-----------
>  drivers/base/dd.c   |   91 ++++++++++++++++++++++++++++++++++++++++-----------
>  3 files changed, 77 insertions(+), 39 deletions(-)
> 
> diff --git a/drivers/base/base.h b/drivers/base/base.h
> index 7a419a7a6235..3f22ebd6117a 100644
> --- a/drivers/base/base.h
> +++ b/drivers/base/base.h
> @@ -124,6 +124,8 @@ extern int driver_add_groups(struct device_driver *drv,
>  			     const struct attribute_group **groups);
>  extern void driver_remove_groups(struct device_driver *drv,
>  				 const struct attribute_group **groups);
> +int device_driver_attach(struct device_driver *drv, struct device *dev);
> +void device_driver_detach(struct device *dev);
>  
>  extern char *make_class_name(const char *name, struct kobject *kobj);
>  
> diff --git a/drivers/base/bus.c b/drivers/base/bus.c
> index 8bfd27ec73d6..8a630f9bd880 100644
> --- a/drivers/base/bus.c
> +++ b/drivers/base/bus.c
> @@ -184,11 +184,7 @@ static ssize_t unbind_store(struct device_driver *drv, const char *buf,
>  
>  	dev = bus_find_device_by_name(bus, NULL, buf);
>  	if (dev && dev->driver == drv) {
> -		if (dev->parent && dev->bus->need_parent_lock)
> -			device_lock(dev->parent);
> -		device_release_driver(dev);
> -		if (dev->parent && dev->bus->need_parent_lock)
> -			device_unlock(dev->parent);
> +		device_driver_detach(dev);
>  		err = count;
>  	}
>  	put_device(dev);
> @@ -211,13 +207,7 @@ static ssize_t bind_store(struct device_driver *drv, const char *buf,
>  
>  	dev = bus_find_device_by_name(bus, NULL, buf);
>  	if (dev && dev->driver == NULL && driver_match_device(drv, dev)) {
> -		if (dev->parent && bus->need_parent_lock)
> -			device_lock(dev->parent);
> -		device_lock(dev);
> -		err = driver_probe_device(drv, dev);
> -		device_unlock(dev);
> -		if (dev->parent && bus->need_parent_lock)
> -			device_unlock(dev->parent);
> +		err = device_driver_attach(drv, dev);
>  
>  		if (err > 0) {
>  			/* success */
> @@ -769,13 +759,8 @@ EXPORT_SYMBOL_GPL(bus_rescan_devices);
>   */
>  int device_reprobe(struct device *dev)
>  {
> -	if (dev->driver) {
> -		if (dev->parent && dev->bus->need_parent_lock)
> -			device_lock(dev->parent);
> -		device_release_driver(dev);
> -		if (dev->parent && dev->bus->need_parent_lock)
> -			device_unlock(dev->parent);
> -	}
> +	if (dev->driver)
> +		device_driver_detach(dev);
>  	return bus_rescan_devices_helper(dev, NULL);
>  }
>  EXPORT_SYMBOL_GPL(device_reprobe);
> diff --git a/drivers/base/dd.c b/drivers/base/dd.c
> index ef3f70a7cb5a..d2515520569e 100644
> --- a/drivers/base/dd.c
> +++ b/drivers/base/dd.c
> @@ -875,6 +875,60 @@ void device_initial_probe(struct device *dev)
>  	__device_attach(dev, true);
>  }
>  
> +/*
> + * __device_driver_lock - acquire locks needed to manipulate dev->drv
> + * @dev: Device we will update driver info for
> + * @parent: Parent device. Needed if the bus requires parent lock
> + *
> + * This function will take the required locks for manipulating dev->drv.
> + * Normally this will just be the @dev lock, but when called for a USB
> + * interface, @parent lock will be held as well.
> + */
> +static void __device_driver_lock(struct device *dev, struct device *parent)
> +{
> +	if (parent && dev->bus->need_parent_lock)
> +		device_lock(parent);
> +	device_lock(dev);
> +}
> +
> +/*
> + * __device_driver_unlock - release locks needed to manipulate dev->drv
> + * @dev: Device we will update driver info for
> + * @parent: Parent device. Needed if the bus requires parent lock
> + *
> + * This function will release the required locks for manipulating dev->drv.
> + * Normally this will just be the the @dev lock, but when called for a
> + * USB interface, @parent lock will be released as well.
> + */
> +static void __device_driver_unlock(struct device *dev, struct device *parent)
> +{
> +	device_unlock(dev);
> +	if (parent && dev->bus->need_parent_lock)
> +		device_unlock(parent);
> +}
> +
> +/**
> + * device_driver_attach - attach a specific driver to a specific device
> + * @drv: Driver to attach
> + * @dev: Device to attach it to
> + *
> + * Manually attach driver to a device. Will acquire both @dev lock and
> + * @dev->parent lock if needed.
> + */
> +int device_driver_attach(struct device_driver *drv, struct device *dev)
> +{
> +	int ret = 0;
> +
> +	__device_driver_lock(dev, dev->parent);
> +
> +	if (!dev->driver)
> +		ret = driver_probe_device(drv, dev);
> +
> +	__device_driver_unlock(dev, dev->parent);
> +
> +	return ret;
> +}
> +
>  static int __driver_attach(struct device *dev, void *data)
>  {
>  	struct device_driver *drv = data;
> @@ -902,14 +956,7 @@ static int __driver_attach(struct device *dev, void *data)
>  		return ret;
>  	} /* ret > 0 means positive match */
>  
> -	if (dev->parent && dev->bus->need_parent_lock)
> -		device_lock(dev->parent);
> -	device_lock(dev);
> -	if (!dev->driver)
> -		driver_probe_device(drv, dev);
> -	device_unlock(dev);
> -	if (dev->parent && dev->bus->need_parent_lock)
> -		device_unlock(dev->parent);
> +	device_driver_attach(drv, dev);
>  
>  	return 0;
>  }
> @@ -948,15 +995,11 @@ static void __device_release_driver(struct device *dev, struct device *parent)
>  	drv = dev->driver;
>  	if (drv) {
>  		while (device_links_busy(dev)) {
> -			device_unlock(dev);
> -			if (parent)
> -				device_unlock(parent);
> +			__device_driver_unlock(dev, parent);
>  
>  			device_links_unbind_consumers(dev);
> -			if (parent)
> -				device_lock(parent);
>  
> -			device_lock(dev);
> +			__device_driver_lock(dev, parent);
>  			/*
>  			 * A concurrent invocation of the same function might
>  			 * have released the driver successfully while this one
> @@ -1009,16 +1052,12 @@ void device_release_driver_internal(struct device *dev,
>  				    struct device_driver *drv,
>  				    struct device *parent)
>  {
> -	if (parent && dev->bus->need_parent_lock)
> -		device_lock(parent);
> +	__device_driver_lock(dev, parent);
>  
> -	device_lock(dev);
>  	if (!drv || drv == dev->driver)
>  		__device_release_driver(dev, parent);
>  
> -	device_unlock(dev);
> -	if (parent && dev->bus->need_parent_lock)
> -		device_unlock(parent);
> +	__device_driver_unlock(dev, parent);
>  }
>  
>  /**
> @@ -1043,6 +1082,18 @@ void device_release_driver(struct device *dev)
>  }
>  EXPORT_SYMBOL_GPL(device_release_driver);
>  
> +/**
> + * device_driver_detach - detach driver from a specific device
> + * @dev: device to detach driver from
> + *
> + * Detach driver from device. Will acquire both @dev lock and @dev->parent
> + * lock if needed.
> + */
> +void device_driver_detach(struct device *dev)
> +{
> +	device_release_driver_internal(dev, NULL, dev->parent);
> +}
> +
>  /**
>   * driver_detach - detach driver from all devices it controls.
>   * @drv: driver.
>