Re: [driver-core PATCH v9 1/9] driver core: Establish order of operations for device_add and device_del via bitflag

[Greg KH <gregkh@linuxfoundation.org>]

On Wed, Dec 12, 2018 at 04:44:58PM -0800, Alexander Duyck wrote:
> Add an additional bit flag to the device struct named "dead".
> 
> This additional flag provides a guarantee that when a device_del is
> executed on a given interface an async worker will not attempt to attach
> the driver following the earlier device_del call. Previously this
> guarantee was not present and could result in the device_del call
> attempting to remove a driver from an interface only to have the async
> worker attempt to probe the driver later when it finally completes the
> asynchronous probe call.
> 
> One additional change added was that I pulled the check for dev->driver
> out of the __device_attach_driver call and instead placed it in the
> __device_attach_async_helper call. This was motivated by the fact that the
> only other caller of this, __device_attach, had already taken the
> device_lock() and checked for dev->driver. Instead of testing for this
> twice in this path it makes more sense to just consolidate the dev->dead
> and dev->driver checks together into one set of checks.
> 
> Reviewed-by: Dan Williams <dan.j.williams@intel.com>
> Signed-off-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
> Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> ---
>  drivers/base/core.c    |   11 +++++++++++
>  drivers/base/dd.c      |   22 +++++++++++-----------
>  include/linux/device.h |    5 +++++
>  3 files changed, 27 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/base/core.c b/drivers/base/core.c
> index 0073b09bb99f..950e25495726 100644
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -2080,6 +2080,17 @@ void device_del(struct device *dev)
>  	struct kobject *glue_dir = NULL;
>  	struct class_interface *class_intf;
>  
> +	/*
> +	 * Hold the device lock and set the "dead" flag to guarantee that
> +	 * the update behavior is consistent with the other bitfields near
> +	 * it and that we cannot have an asynchronous probe routine trying
> +	 * to run while we are tearing out the bus/class/sysfs from
> +	 * underneath the device.
> +	 */
> +	device_lock(dev);
> +	dev->dead = true;
> +	device_unlock(dev);
> +
>  	/* Notify clients of device removal.  This call must come
>  	 * before dpm_sysfs_remove().
>  	 */
> diff --git a/drivers/base/dd.c b/drivers/base/dd.c
> index 88713f182086..74c194ac99df 100644
> --- a/drivers/base/dd.c
> +++ b/drivers/base/dd.c
> @@ -731,15 +731,6 @@ static int __device_attach_driver(struct device_driver *drv, void *_data)
>  	bool async_allowed;
>  	int ret;
>  
> -	/*
> -	 * Check if device has already been claimed. This may
> -	 * happen with driver loading, device discovery/registration,
> -	 * and deferred probe processing happens all at once with
> -	 * multiple threads.
> -	 */
> -	if (dev->driver)
> -		return -EBUSY;
> -
>  	ret = driver_match_device(drv, dev);
>  	if (ret == 0) {
>  		/* no match */
> @@ -774,6 +765,15 @@ static void __device_attach_async_helper(void *_dev, async_cookie_t cookie)
>  
>  	device_lock(dev);
>  
> +	/*
> +	 * Check if device has already been removed or claimed. This may
> +	 * happen with driver loading, device discovery/registration,
> +	 * and deferred probe processing happens all at once with
> +	 * multiple threads.
> +	 */
> +	if (dev->dead || dev->driver)
> +		goto out_unlock;
> +
>  	if (dev->parent)
>  		pm_runtime_get_sync(dev->parent);
>  
> @@ -784,7 +784,7 @@ static void __device_attach_async_helper(void *_dev, async_cookie_t cookie)
>  
>  	if (dev->parent)
>  		pm_runtime_put(dev->parent);
> -
> +out_unlock:
>  	device_unlock(dev);
>  
>  	put_device(dev);
> @@ -897,7 +897,7 @@ static int __driver_attach(struct device *dev, void *data)
>  	if (dev->parent && dev->bus->need_parent_lock)
>  		device_lock(dev->parent);
>  	device_lock(dev);
> -	if (!dev->driver)
> +	if (!dev->dead && !dev->driver)
>  		driver_probe_device(drv, dev);
>  	device_unlock(dev);
>  	if (dev->parent && dev->bus->need_parent_lock)
> diff --git a/include/linux/device.h b/include/linux/device.h
> index 1b25c7a43f4c..f73dad81e811 100644
> --- a/include/linux/device.h
> +++ b/include/linux/device.h
> @@ -957,6 +957,10 @@ struct dev_links_info {
>   *              device.
>   * @dma_coherent: this particular device is dma coherent, even if the
>   *		architecture supports non-coherent devices.
> + * @dead:	This device is currently either in the process of or has
> + *		been removed from the system. Any asynchronous events
> + *		scheduled for this device should exit without taking any
> + *		action.
>   *
>   * At the lowest level, every device in a Linux system is represented by an
>   * instance of struct device. The device structure contains the information
> @@ -1051,6 +1055,7 @@ struct device {
>      defined(CONFIG_ARCH_HAS_SYNC_DMA_FOR_CPU_ALL)
>  	bool			dma_coherent:1;
>  #endif
> +	bool			dead:1;

This really should live in the struct device_private structure, as
nothing outside of the driver core should care about this, or touch it.

A number of other bitfields should also move there as well, your's isn't
the only one that I missed this for.

So can you make that quick change, and rebase (you needed to for patch 2
anyway), and resend so I can get this into my -next tree for people to
start testing and basing their work on?

sorry this has taken so long, and thanks for sticking with it.

greg k-h
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