drm/ttm: Make sure a sync object doesn't disappear while we use it

The sync object may disappear as soon as we release the bo::lock, so
take a reference on it while we use it.
One option would be to call sync_object_flush() before releasing the bo::lock,
but that would put an atomic requirement on that function.

Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

1 files changed, 7 insertions, 4 deletions

diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
index a32fe41e5e24..340dfb11959d 100644
--- a/drivers/gpu/drm/ttm/ttm_bo.c
+++ b/drivers/gpu/drm/ttm/ttm_bo.c
@@ -458,7 +458,7 @@ static void ttm_bo_cleanup_refs_or_queue(struct ttm_buffer_object *bo)
         struct ttm_bo_device *bdev = bo->bdev;
         struct ttm_bo_global *glob = bo->glob;
         struct ttm_bo_driver *driver;
-        void *sync_obj;
+        void *sync_obj = NULL;
         void *sync_obj_arg;
         int put_count;
         int ret;
@@ -493,17 +493,20 @@ static void ttm_bo_cleanup_refs_or_queue(struct ttm_buffer_object *bo)
                 spin_lock(&glob->lru_lock);
         }
 queue:
-        sync_obj = bo->sync_obj;
-        sync_obj_arg = bo->sync_obj_arg;
         driver = bdev->driver;
+        if (bo->sync_obj)
+                sync_obj = driver->sync_obj_ref(bo->sync_obj);
+        sync_obj_arg = bo->sync_obj_arg;
 
         kref_get(&bo->list_kref);
         list_add_tail(&bo->ddestroy, &bdev->ddestroy);
         spin_unlock(&glob->lru_lock);
         spin_unlock(&bo->lock);
 
-        if (sync_obj)
+        if (sync_obj) {
                 driver->sync_obj_flush(sync_obj, sync_obj_arg);
+                driver->sync_obj_unref(&sync_obj);
+        }
         schedule_delayed_work(&bdev->wq,
                               ((HZ / 100) < 1) ? 1 : HZ / 100);
 }