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Commit bee330f3 authored by Noralf Trønnes's avatar Noralf Trønnes Committed by Oleksandr Andrushchenko
Browse files

drm: Use srcu to protect drm_device.unplugged 



Use srcu to protect drm_device.unplugged in a race free manner.
Drivers can use drm_dev_enter()/drm_dev_exit() to protect and mark
sections preventing access to device resources that are not available
after the device is gone.

Suggested-by: default avatarDaniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: default avatarNoralf Trønnes <noralf@tronnes.org>
Signed-off-by: default avatarOleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
Reviewed-by: default avatarOleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
Tested-by: default avatarOleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
Cc: intel-gfx@lists.freedesktop.org
Reviewed-by: default avatarDaniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/1522222715-11814-1-git-send-email-andr2000@gmail.com
parent 790861cc

drivers/gpu/drm/drm_drv.c

+49 −5
Original line number Diff line number Diff line
@@ -32,6 +32,7 @@ 
#include <linux/moduleparam.h>

#include <linux/mount.h>

#include <linux/slab.h>

#include <linux/srcu.h>



#include <drm/drm_drv.h>

#include <drm/drmP.h>
@@ -75,6 +76,8 @@ static bool drm_core_init_complete = false; 


static struct dentry *drm_debugfs_root;



DEFINE_STATIC_SRCU(drm_unplug_srcu);



/*

 * DRM Minors

 * A DRM device can provide several char-dev interfaces on the DRM-Major. Each
@@ -318,18 +321,51 @@ void drm_put_dev(struct drm_device *dev) 
}

EXPORT_SYMBOL(drm_put_dev);



static void drm_device_set_unplugged(struct drm_device *dev)

/**

 * drm_dev_enter - Enter device critical section

 * @dev: DRM device

 * @idx: Pointer to index that will be passed to the matching drm_dev_exit()

 *

 * This function marks and protects the beginning of a section that should not

 * be entered after the device has been unplugged. The section end is marked

 * with drm_dev_exit(). Calls to this function can be nested.

 *

 * Returns:

 * True if it is OK to enter the section, false otherwise.

 */

bool drm_dev_enter(struct drm_device *dev, int *idx)

{

	*idx = srcu_read_lock(&drm_unplug_srcu);



	if (dev->unplugged) {

		srcu_read_unlock(&drm_unplug_srcu, *idx);

		return false;

	}



	return true;

}

EXPORT_SYMBOL(drm_dev_enter);



/**

 * drm_dev_exit - Exit device critical section

 * @idx: index returned from drm_dev_enter()

 *

 * This function marks the end of a section that should not be entered after

 * the device has been unplugged.

 */

void drm_dev_exit(int idx)

{

	smp_wmb();

	atomic_set(&dev->unplugged, 1);

	srcu_read_unlock(&drm_unplug_srcu, idx);

}

EXPORT_SYMBOL(drm_dev_exit);



/**

 * drm_dev_unplug - unplug a DRM device

 * @dev: DRM device

 *

 * This unplugs a hotpluggable DRM device, which makes it inaccessible to

 * userspace operations. Entry-points can use drm_dev_is_unplugged(). This

 * userspace operations. Entry-points can use drm_dev_enter() and

 * drm_dev_exit() to protect device resources in a race free manner. This

 * essentially unregisters the device like drm_dev_unregister(), but can be

 * called while there are still open users of @dev.

 */
@@ -338,10 +374,18 @@ void drm_dev_unplug(struct drm_device *dev) 
	drm_dev_unregister(dev);



	mutex_lock(&drm_global_mutex);

	drm_device_set_unplugged(dev);

	if (dev->open_count == 0)

		drm_dev_put(dev);

	mutex_unlock(&drm_global_mutex);



	/*

	 * After synchronizing any critical read section is guaranteed to see

	 * the new value of ->unplugged, and any critical section which might

	 * still have seen the old value of ->unplugged is guaranteed to have

	 * finished.

	 */

	dev->unplugged = true;

	synchronize_srcu(&drm_unplug_srcu);

}

EXPORT_SYMBOL(drm_dev_unplug);

include/drm/drm_device.h

+8 −1
Original line number Diff line number Diff line
@@ -46,7 +46,14 @@ struct drm_device { 
	/* currently active master for this device. Protected by master_mutex */

	struct drm_master *master;



	atomic_t unplugged;			/**< Flag whether dev is dead */

	/**

	 * @unplugged:

	 *

	 * Flag to tell if the device has been unplugged.

	 * See drm_dev_enter() and drm_dev_is_unplugged().

	 */

	bool unplugged;



	struct inode *anon_inode;		/**< inode for private address-space */

	char *unique;				/**< unique name of the device */

	/*@} */

include/drm/drm_drv.h

+11 −4
Original line number Diff line number Diff line
@@ -623,6 +623,8 @@ void drm_dev_get(struct drm_device *dev); 
void drm_dev_put(struct drm_device *dev);

void drm_dev_unref(struct drm_device *dev);

void drm_put_dev(struct drm_device *dev);

bool drm_dev_enter(struct drm_device *dev, int *idx);

void drm_dev_exit(int idx);

void drm_dev_unplug(struct drm_device *dev);



/**
@@ -634,11 +636,16 @@ void drm_dev_unplug(struct drm_device *dev); 
 * unplugged, these two functions guarantee that any store before calling

 * drm_dev_unplug() is visible to callers of this function after it completes

 */

static inline int drm_dev_is_unplugged(struct drm_device *dev)

static inline bool drm_dev_is_unplugged(struct drm_device *dev)

{

	int ret = atomic_read(&dev->unplugged);

	smp_rmb();

	return ret;

	int idx;



	if (drm_dev_enter(dev, &idx)) {

		drm_dev_exit(idx);

		return false;

	}



	return true;

}