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: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
Reviewed-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
Tested-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
Cc: intel-gfx@lists.freedesktop.org
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/1522222715-11814-1-git-send-email-andr2000@gmail.com

1 files changed, 11 insertions, 4 deletions

diff --git a/include/drm/drm_drv.h b/include/drm/drm_drv.h
index d32b688..ff7312c 100644
--- a/include/drm/drm_drv.h
+++ b/include/drm/drm_drv.h
@@ -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;
 }