Revert "drm/vkms: Fix race-condition between the hrtimer and the atomic commit"

This reverts commit a0e6a01.

Unlocking a mutex in the context of a hrtimer callback is violating mutex
locking rules, as mutex_unlock() from interrupt context is not permitted.

Link: https://lore.kernel.org/dri-devel/ZQLAc%2FFwkv%2FGiVoK@phenom.ffwll.local/T/#t
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Maíra Canal <mcanal@igalia.com>
Signed-off-by: Maíra Canal <mairacanal@riseup.net>
Link: https://patchwork.freedesktop.org/patch/msgid/20230914102024.1789154-1-mcanal@igalia.com

Author: mairacanal

drivers/gpu/drm/vkms/vkms_composer.c

@@ -408,15 +408,10 @@ void vkms_set_composer(struct vkms_output *out, bool enabled)
 	if (enabled)
 		drm_crtc_vblank_get(&out->crtc);
 
-	mutex_lock(&out->enabled_lock);
+	spin_lock_irq(&out->lock);
 	old_enabled = out->composer_enabled;
 	out->composer_enabled = enabled;
-
-	/* the composition wasn't enabled, so unlock the lock to make sure the lock
-	 * will be balanced even if we have a failed commit
-	 */
-	if (!out->composer_enabled)
-		mutex_unlock(&out->enabled_lock);
+	spin_unlock_irq(&out->lock);
 
 	if (old_enabled)
 		drm_crtc_vblank_put(&out->crtc);

drivers/gpu/drm/vkms/vkms_crtc.c

@@ -16,7 +16,7 @@ static enum hrtimer_restart vkms_vblank_simulate(struct hrtimer *timer)
 	struct drm_crtc *crtc = &output->crtc;
 	struct vkms_crtc_state *state;
 	u64 ret_overrun;
-	bool ret, fence_cookie, composer_enabled;
+	bool ret, fence_cookie;
 
 	fence_cookie = dma_fence_begin_signalling();
 
@@ -25,15 +25,15 @@ static enum hrtimer_restart vkms_vblank_simulate(struct hrtimer *timer)
 	if (ret_overrun != 1)
 		pr_warn("%s: vblank timer overrun\n", __func__);
 
+	spin_lock(&output->lock);
 	ret = drm_crtc_handle_vblank(crtc);
 	if (!ret)
 		DRM_ERROR("vkms failure on handling vblank");
 
 	state = output->composer_state;
-	composer_enabled = output->composer_enabled;
-	mutex_unlock(&output->enabled_lock);
+	spin_unlock(&output->lock);
 
-	if (state && composer_enabled) {
+	if (state && output->composer_enabled) {
 		u64 frame = drm_crtc_accurate_vblank_count(crtc);
 
 		/* update frame_start only if a queued vkms_composer_worker()
@@ -295,7 +295,6 @@ int vkms_crtc_init(struct drm_device *dev, struct drm_crtc *crtc,
 
 	spin_lock_init(&vkms_out->lock);
 	spin_lock_init(&vkms_out->composer_lock);
-	mutex_init(&vkms_out->enabled_lock);
 
 	vkms_out->composer_workq = alloc_ordered_workqueue("vkms_composer", 0);
 	if (!vkms_out->composer_workq)

drivers/gpu/drm/vkms/vkms_drv.h

@@ -108,10 +108,8 @@ struct vkms_output {
 	struct workqueue_struct *composer_workq;
 	/* protects concurrent access to composer */
 	spinlock_t lock;
-	/* guarantees that if the composer is enabled, a job will be queued */
-	struct mutex enabled_lock;
 
-	/* protected by @enabled_lock */
+	/* protected by @lock */
 	bool composer_enabled;
 	struct vkms_crtc_state *composer_state;