drm/radeon: fix oops in ttm reserve when pageflipping (v2)

We need to take a reference to this object, pinning doesn't take a reference
so if userspace deletes the object it can disappear even if pinned.

v2: fix error paths to unreference properly also.

should fix:
https://bugzilla.kernel.org/show_bug.cgi?id=32402
and
https://bugzilla.redhat.com/show_bug.cgi?id=680651

Acked-By: Alex Deucher <alexdeucher@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

1 files changed, 8 insertions, 5 deletions

diff --git a/drivers/gpu/drm/radeon/radeon_display.c b/drivers/gpu/drm/radeon/radeon_display.c
index ae247eec87c0..292f73f0ddbd 100644
--- a/drivers/gpu/drm/radeon/radeon_display.c
+++ b/drivers/gpu/drm/radeon/radeon_display.c
@@ -264,6 +264,8 @@ static void radeon_unpin_work_func(struct work_struct *__work)
                 radeon_bo_unreserve(work->old_rbo);
         } else
                 DRM_ERROR("failed to reserve buffer after flip\n");
+
+        drm_gem_object_unreference_unlocked(&work->old_rbo->gem_base);
         kfree(work);
 }
 
@@ -371,6 +373,8 @@ static int radeon_crtc_page_flip(struct drm_crtc *crtc,
         new_radeon_fb = to_radeon_framebuffer(fb);
         /* schedule unpin of the old buffer */
         obj = old_radeon_fb->obj;
+        /* take a reference to the old object */
+        drm_gem_object_reference(obj);
         rbo = gem_to_radeon_bo(obj);
         work->old_rbo = rbo;
         INIT_WORK(&work->work, radeon_unpin_work_func);
@@ -378,12 +382,9 @@ static int radeon_crtc_page_flip(struct drm_crtc *crtc,
         /* We borrow the event spin lock for protecting unpin_work */
         spin_lock_irqsave(&dev->event_lock, flags);
         if (radeon_crtc->unpin_work) {
-                spin_unlock_irqrestore(&dev->event_lock, flags);
-                kfree(work);
-                radeon_fence_unref(&fence);
-
                 DRM_DEBUG_DRIVER("flip queue: crtc already busy\n");
-                return -EBUSY;
+                r = -EBUSY;
+                goto unlock_free;
         }
         radeon_crtc->unpin_work = work;
         radeon_crtc->deferred_flip_completion = 0;
@@ -497,6 +498,8 @@ pflip_cleanup1:
 pflip_cleanup:
         spin_lock_irqsave(&dev->event_lock, flags);
         radeon_crtc->unpin_work = NULL;
+unlock_free:
+        drm_gem_object_unreference_unlocked(old_radeon_fb->obj);
         spin_unlock_irqrestore(&dev->event_lock, flags);
         radeon_fence_unref(&fence);
         kfree(work);