drm/ttm: change fence_lock to inner lock

This requires changing the order in ttm_bo_cleanup_refs_or_queue to
take the reservation first, as there is otherwise no race free way to
take lru lock before fence_lock.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@canonical.com>
Reviewed-by: Thomas Hellstrom <thellstrom@vmware.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

2 files changed, 13 insertions, 22 deletions

diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
index 2c54c3d414b3..b7781453bfd1 100644
--- a/drivers/gpu/drm/ttm/ttm_bo.c
+++ b/drivers/gpu/drm/ttm/ttm_bo.c
@@ -500,27 +500,17 @@ 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;
+        struct ttm_bo_driver *driver = bdev->driver;
         void *sync_obj = NULL;
         int put_count;
         int ret;
 
+        spin_lock(&glob->lru_lock);
+        ret = ttm_bo_reserve_locked(bo, false, true, false, 0);
+
         spin_lock(&bdev->fence_lock);
         (void) ttm_bo_wait(bo, false, false, true);
-        if (!bo->sync_obj) {
-
-                spin_lock(&glob->lru_lock);
-
-                /**
-                 * Lock inversion between bo:reserve and bdev::fence_lock here,
-                 * but that's OK, since we're only trylocking.
-                 */
-
-                ret = ttm_bo_reserve_locked(bo, false, true, false, 0);
-
-                if (unlikely(ret == -EBUSY))
-                        goto queue;
-
+        if (!ret && !bo->sync_obj) {
                 spin_unlock(&bdev->fence_lock);
                 put_count = ttm_bo_del_from_lru(bo);
 
@@ -530,18 +520,19 @@ static void ttm_bo_cleanup_refs_or_queue(struct ttm_buffer_object *bo)
                 ttm_bo_list_ref_sub(bo, put_count, true);
 
                 return;
-        } else {
-                spin_lock(&glob->lru_lock);
         }
-queue:
-        driver = bdev->driver;
         if (bo->sync_obj)
                 sync_obj = driver->sync_obj_ref(bo->sync_obj);
+        spin_unlock(&bdev->fence_lock);
+
+        if (!ret) {
+                atomic_set(&bo->reserved, 0);
+                wake_up_all(&bo->event_queue);
+        }
 
         kref_get(&bo->list_kref);
         list_add_tail(&bo->ddestroy, &bdev->ddestroy);
         spin_unlock(&glob->lru_lock);
-        spin_unlock(&bdev->fence_lock);
 
         if (sync_obj) {
                 driver->sync_obj_flush(sync_obj);
diff --git a/drivers/gpu/drm/ttm/ttm_execbuf_util.c b/drivers/gpu/drm/ttm/ttm_execbuf_util.c
index 1986d006c264..cd9e4523dc56 100644
--- a/drivers/gpu/drm/ttm/ttm_execbuf_util.c
+++ b/drivers/gpu/drm/ttm/ttm_execbuf_util.c
@@ -213,8 +213,8 @@ void ttm_eu_fence_buffer_objects(struct list_head *list, void *sync_obj)
         driver = bdev->driver;
         glob = bo->glob;
 
-        spin_lock(&bdev->fence_lock);
         spin_lock(&glob->lru_lock);
+        spin_lock(&bdev->fence_lock);
 
         list_for_each_entry(entry, list, head) {
                 bo = entry->bo;
@@ -223,8 +223,8 @@ void ttm_eu_fence_buffer_objects(struct list_head *list, void *sync_obj)
                 ttm_bo_unreserve_locked(bo);
                 entry->reserved = false;
         }
-        spin_unlock(&glob->lru_lock);
         spin_unlock(&bdev->fence_lock);
+        spin_unlock(&glob->lru_lock);
 
         list_for_each_entry(entry, list, head) {
                 if (entry->old_sync_obj)