drm/ttm, drm/vmwgfx: Use RCU locking for object lookups v3

The mostly used lookup+get put+potential_destroy path of TTM objects
is converted to use RCU locks. This will substantially decrease the amount
of locked bus cycles during normal operation.
Since we use kfree_rcu to free the objects, no rcu synchronization is needed
at module unload time.

v2: Don't touch include/linux/kref.h
v3: Adapt to kref_get_unless_zero return value change

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

1 files changed, 11 insertions, 19 deletions

diff --git a/drivers/gpu/drm/ttm/ttm_object.c b/drivers/gpu/drm/ttm/ttm_object.c
index c7857874956a..f18eeb458139 100644
--- a/drivers/gpu/drm/ttm/ttm_object.c
+++ b/drivers/gpu/drm/ttm/ttm_object.c
@@ -80,7 +80,7 @@ struct ttm_object_file {
  */
 
 struct ttm_object_device {
-        rwlock_t object_lock;
+        spinlock_t object_lock;
         struct drm_open_hash object_hash;
         atomic_t object_count;
         struct ttm_mem_global *mem_glob;
@@ -157,12 +157,12 @@ int ttm_base_object_init(struct ttm_object_file *tfile,
         base->refcount_release = refcount_release;
         base->ref_obj_release = ref_obj_release;
         base->object_type = object_type;
-        write_lock(&tdev->object_lock);
+        spin_lock(&tdev->object_lock);
         kref_init(&base->refcount);
         ret = drm_ht_just_insert_please(&tdev->object_hash,
                                         &base->hash,
                                         (unsigned long)base, 31, 0, 0);
-        write_unlock(&tdev->object_lock);
+        spin_unlock(&tdev->object_lock);
         if (unlikely(ret != 0))
                 goto out_err0;
 
@@ -186,30 +186,22 @@ static void ttm_release_base(struct kref *kref)
             container_of(kref, struct ttm_base_object, refcount);
         struct ttm_object_device *tdev = base->tfile->tdev;
 
+        spin_lock(&tdev->object_lock);
         (void)drm_ht_remove_item(&tdev->object_hash, &base->hash);
-        write_unlock(&tdev->object_lock);
+        spin_unlock(&tdev->object_lock);
         if (base->refcount_release) {
                 ttm_object_file_unref(&base->tfile);
                 base->refcount_release(&base);
         }
-        write_lock(&tdev->object_lock);
 }
 
 void ttm_base_object_unref(struct ttm_base_object **p_base)
 {
         struct ttm_base_object *base = *p_base;
-        struct ttm_object_device *tdev = base->tfile->tdev;
 
         *p_base = NULL;
 
-        /*
-         * Need to take the lock here to avoid racing with
-         * users trying to look up the object.
-         */
-
-        write_lock(&tdev->object_lock);
         kref_put(&base->refcount, ttm_release_base);
-        write_unlock(&tdev->object_lock);
 }
 EXPORT_SYMBOL(ttm_base_object_unref);
 
@@ -221,14 +213,14 @@ struct ttm_base_object *ttm_base_object_lookup(struct ttm_object_file *tfile,
         struct drm_hash_item *hash;
         int ret;
 
-        read_lock(&tdev->object_lock);
+        rcu_read_lock();
         ret = drm_ht_find_item(&tdev->object_hash, key, &hash);
 
         if (likely(ret == 0)) {
                 base = drm_hash_entry(hash, struct ttm_base_object, hash);
-                kref_get(&base->refcount);
+                ret = kref_get_unless_zero(&base->refcount) ? 0 : -EINVAL;
         }
-        read_unlock(&tdev->object_lock);
+        rcu_read_unlock();
 
         if (unlikely(ret != 0))
                 return NULL;
@@ -426,7 +418,7 @@ struct ttm_object_device *ttm_object_device_init(struct ttm_mem_global
                 return NULL;
 
         tdev->mem_glob = mem_glob;
-        rwlock_init(&tdev->object_lock);
+        spin_lock_init(&tdev->object_lock);
         atomic_set(&tdev->object_count, 0);
         ret = drm_ht_create(&tdev->object_hash, hash_order);
 
@@ -444,9 +436,9 @@ void ttm_object_device_release(struct ttm_object_device **p_tdev)
 
         *p_tdev = NULL;
 
-        write_lock(&tdev->object_lock);
+        spin_lock(&tdev->object_lock);
         drm_ht_remove(&tdev->object_hash);
-        write_unlock(&tdev->object_lock);
+        spin_unlock(&tdev->object_lock);
 
         kfree(tdev);
 }