drm/ttm: Add a ttm_ref_object_exists function

A function to be used to check whether a caller has put a ref object
(opened) a struct ttm_base_object

Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Reviewed-by: Brian Paul <brianp@vmware.com>

2 files changed, 50 insertions, 0 deletions

diff --git a/drivers/gpu/drm/ttm/ttm_object.c b/drivers/gpu/drm/ttm/ttm_object.c
index 53b51c4e671a..d2a053352789 100644
--- a/drivers/gpu/drm/ttm/ttm_object.c
+++ b/drivers/gpu/drm/ttm/ttm_object.c
@@ -270,6 +270,52 @@ ttm_base_object_lookup_for_ref(struct ttm_object_device *tdev, uint32_t key)
 }
 EXPORT_SYMBOL(ttm_base_object_lookup_for_ref);
 
+/**
+ * ttm_ref_object_exists - Check whether a caller has a valid ref object
+ * (has opened) a base object.
+ *
+ * @tfile: Pointer to a struct ttm_object_file identifying the caller.
+ * @base: Pointer to a struct base object.
+ *
+ * Checks wether the caller identified by @tfile has put a valid USAGE
+ * reference object on the base object identified by @base.
+ */
+bool ttm_ref_object_exists(struct ttm_object_file *tfile,
+                           struct ttm_base_object *base)
+{
+        struct drm_open_hash *ht = &tfile->ref_hash[TTM_REF_USAGE];
+        struct drm_hash_item *hash;
+        struct ttm_ref_object *ref;
+
+        rcu_read_lock();
+        if (unlikely(drm_ht_find_item_rcu(ht, base->hash.key, &hash) != 0))
+                goto out_false;
+
+        /*
+         * Verify that the ref object is really pointing to our base object.
+         * Our base object could actually be dead, and the ref object pointing
+         * to another base object with the same handle.
+         */
+        ref = drm_hash_entry(hash, struct ttm_ref_object, hash);
+        if (unlikely(base != ref->obj))
+                goto out_false;
+
+        /*
+         * Verify that the ref->obj pointer was actually valid!
+         */
+        rmb();
+        if (unlikely(atomic_read(&ref->kref.refcount) == 0))
+                goto out_false;
+
+        rcu_read_unlock();
+        return true;
+
+ out_false:
+        rcu_read_unlock();
+        return false;
+}
+EXPORT_SYMBOL(ttm_ref_object_exists);
+
 int ttm_ref_object_add(struct ttm_object_file *tfile,
                        struct ttm_base_object *base,
                        enum ttm_ref_type ref_type, bool *existed)
diff --git a/include/drm/ttm/ttm_object.h b/include/drm/ttm/ttm_object.h
index 0097cc03034e..ed953f98f0e1 100644
--- a/include/drm/ttm/ttm_object.h
+++ b/include/drm/ttm/ttm_object.h
@@ -244,6 +244,10 @@ extern void ttm_base_object_unref(struct ttm_base_object **p_base);
 extern int ttm_ref_object_add(struct ttm_object_file *tfile,
                               struct ttm_base_object *base,
                               enum ttm_ref_type ref_type, bool *existed);
+
+extern bool ttm_ref_object_exists(struct ttm_object_file *tfile,
+                                  struct ttm_base_object *base);
+
 /**
  * ttm_ref_object_base_unref
  *