[PATCH 2/2] drm: get lock before accessing vblank refcount

[Yunxiang Li <Yunxiang.Li@amd.com>]

Acquire vbl_lock before accessing vblank refcount in drm_vblank_put,
just like everywhere else that access the refcount.

Signed-off-by: Yunxiang Li <Yunxiang.Li@amd.com>
---
 drivers/gpu/drm/drm_vblank.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
index 159d13b5d97b..77b8c40fc7ba 100644
--- a/drivers/gpu/drm/drm_vblank.c
+++ b/drivers/gpu/drm/drm_vblank.c
@@ -1203,15 +1203,22 @@ EXPORT_SYMBOL(drm_crtc_vblank_get);
 void drm_vblank_put(struct drm_device *dev, unsigned int pipe)
 {
 	struct drm_vblank_crtc *vblank = &dev->vblank[pipe];
+	unsigned long irqflags;
+	int ret;
 
 	if (drm_WARN_ON(dev, pipe >= dev->num_crtcs))
 		return;
 
-	if (drm_WARN_ON(dev, atomic_read(&vblank->refcount) == 0))
+	spin_lock_irqsave(&dev->vbl_lock, irqflags);
+	if (drm_WARN_ON(dev, atomic_read(&vblank->refcount) == 0)) {
+		spin_unlock_irqrestore(&dev->vbl_lock, irqflags);
 		return;
+	}
 
 	/* Last user schedules interrupt disable */
-	if (atomic_dec_and_test(&vblank->refcount)) {
+	ret = atomic_dec_and_test(&vblank->refcount);
+	spin_unlock_irqrestore(&dev->vbl_lock, irqflags);
+	if (ret) {
 		if (drm_vblank_offdelay == 0)
 			return;
 		else if (drm_vblank_offdelay < 0)
-- 
2.37.1