drm/i915: don't set unpin_work if vblank_get fails

This fixes a race where we may try to finish a page flip and decrement
the refcount even if our vblank_get failed and we ended up with a
spurious flip pending interrupt.

Fixes https://bugs.freedesktop.org/show_bug.cgi?id=34211.

Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Keith Packard <keithp@keithp.com>

1 files changed, 7 insertions, 5 deletions

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index d544de9e663..91b5f8707a6 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -7189,11 +7189,16 @@ static int intel_crtc_page_flip(struct drm_crtc *crtc,
         work->old_fb_obj = intel_fb->obj;
         INIT_WORK(&work->work, intel_unpin_work_fn);
 
+        ret = drm_vblank_get(dev, intel_crtc->pipe);
+        if (ret)
+                goto free_work;
+
         /* We borrow the event spin lock for protecting unpin_work */
         spin_lock_irqsave(&dev->event_lock, flags);
         if (intel_crtc->unpin_work) {
                 spin_unlock_irqrestore(&dev->event_lock, flags);
                 kfree(work);
+                drm_vblank_put(dev, intel_crtc->pipe);
 
                 DRM_DEBUG_DRIVER("flip queue: crtc already busy\n");
                 return -EBUSY;
@@ -7212,10 +7217,6 @@ static int intel_crtc_page_flip(struct drm_crtc *crtc,
 
         crtc->fb = fb;
 
-        ret = drm_vblank_get(dev, intel_crtc->pipe);
-        if (ret)
-                goto cleanup_objs;
-
         work->pending_flip_obj = obj;
 
         work->enable_stall_check = true;
@@ -7238,7 +7239,6 @@ static int intel_crtc_page_flip(struct drm_crtc *crtc,
 
 cleanup_pending:
         atomic_sub(1 << intel_crtc->plane, &work->old_fb_obj->pending_flip);
-cleanup_objs:
         drm_gem_object_unreference(&work->old_fb_obj->base);
         drm_gem_object_unreference(&obj->base);
         mutex_unlock(&dev->struct_mutex);
@@ -7247,6 +7247,8 @@ cleanup_objs:
         intel_crtc->unpin_work = NULL;
         spin_unlock_irqrestore(&dev->event_lock, flags);
 
+        drm_vblank_put(dev, intel_crtc->pipe);
+free_work:
         kfree(work);
 
         return ret;