Commit 43dc7fe2 authored by Chris Wilson's avatar Chris Wilson Committed by Ville Syrjälä
Browse files

drm: Mark up accesses of vblank->enabled outside of its spinlock 



Order the update to vblank->enabled after the timestamp is primed so
that a concurrent unlocked reader will only see the vblank->enabled with
the current timestamp.

v2: vblank->enable is guarded by dev->vbl_lock not
dev->vblank_time_lock, update the READ_ONCE accordingly.

Do not add a READ_ONCE(vblank->enabled) inside the interrupt handler to
avoid missing an interrupt whilst racing with enable_vblank()

Signed-off-by: default avatarChris Wilson <chris@chris-wilson.co.uk>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20170317202030.24410-1-chris@chris-wilson.co.uk


Reviewed-by: default avatarVille Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: default avatarVille Syrjälä <ville.syrjala@linux.intel.com>
parent 75cff083

drivers/gpu/drm/drm_irq.c

+14 −9
Original line number Diff line number Diff line
@@ -325,6 +325,8 @@ static void vblank_disable_and_save(struct drm_device *dev, unsigned int pipe) 
	struct drm_vblank_crtc *vblank = &dev->vblank[pipe];

	unsigned long irqflags;



	assert_spin_locked(&dev->vbl_lock);



	/* Prevent vblank irq processing while disabling vblank irqs,

	 * so no updates of timestamps or count can happen after we've

	 * disabled. Needed to prevent races in case of delayed irq's.
@@ -336,10 +338,8 @@ static void vblank_disable_and_save(struct drm_device *dev, unsigned int pipe) 
	 * calling the ->disable_vblank() operation in atomic context with the

	 * hardware potentially runtime suspended.

	 */

	if (vblank->enabled) {

	if (cmpxchg_relaxed(&vblank->enabled, true, false))

		__disable_vblank(dev, pipe);

		vblank->enabled = false;

	}



	/*

	 * Always update the count and timestamp to maintain the
@@ -384,7 +384,7 @@ void drm_vblank_cleanup(struct drm_device *dev) 
	for (pipe = 0; pipe < dev->num_crtcs; pipe++) {

		struct drm_vblank_crtc *vblank = &dev->vblank[pipe];



		WARN_ON(vblank->enabled &&

		WARN_ON(READ_ONCE(vblank->enabled) &&

			drm_core_check_feature(dev, DRIVER_MODESET));



		del_timer_sync(&vblank->disable_timer);
@@ -1097,11 +1097,16 @@ static int drm_vblank_enable(struct drm_device *dev, unsigned int pipe) 
		 */

		ret = __enable_vblank(dev, pipe);

		DRM_DEBUG("enabling vblank on crtc %u, ret: %d\n", pipe, ret);

		if (ret)

		if (ret) {

			atomic_dec(&vblank->refcount);

		else {

			vblank->enabled = true;

		} else {

			drm_update_vblank_count(dev, pipe, 0);

			/* drm_update_vblank_count() includes a wmb so we just

			 * need to ensure that the compiler emits the write

			 * to mark the vblank as enabled after the call

			 * to drm_update_vblank_count().

			 */

			WRITE_ONCE(vblank->enabled, true);

		}

	}
@@ -1509,7 +1514,7 @@ static int drm_queue_vblank_event(struct drm_device *dev, unsigned int pipe, 
	 * vblank disable, so no need for further locking.  The reference from

	 * drm_vblank_get() protects against vblank disable from another source.

	 */

	if (!vblank->enabled) {

	if (!READ_ONCE(vblank->enabled)) {

		ret = -EINVAL;

		goto err_unlock;

	}
@@ -1636,7 +1641,7 @@ int drm_wait_vblank(struct drm_device *dev, void *data, 
		DRM_WAIT_ON(ret, vblank->queue, 3 * HZ,

			    (((drm_vblank_count(dev, pipe) -

			       vblwait->request.sequence) <= (1 << 23)) ||

			     !vblank->enabled ||

			     !READ_ONCE(vblank->enabled) ||

			     !dev->irq_enabled));

	}

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