[PATCH 5.11 074/120] drm/ttm: make ttm_bo_unpin more defensive

[Greg Kroah-Hartman]

From: Christian König <christian.koenig@xxxxxxx>

[ Upstream commit 6c5403173a13a08ff61dbdafa4c0ed4a9dedbfe0 ]

We seem to have some more driver bugs than thought.

Signed-off-by: Christian König <christian.koenig@xxxxxxx>
Fixes: deb0814b43f3 ("drm/ttm: add ttm_bo_pin()/ttm_bo_unpin() v2")
Acked-by: Matthew Auld <matthew.auld@xxxxxxxxx>
Link: https://patchwork.freedesktop.org/patch/msgid/20210312093810.2202-1-christian.koenig@xxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 include/drm/ttm/ttm_bo_api.h | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/include/drm/ttm/ttm_bo_api.h b/include/drm/ttm/ttm_bo_api.h
index 79b9367e0ffd..b5bef3199196 100644
--- a/include/drm/ttm/ttm_bo_api.h
+++ b/include/drm/ttm/ttm_bo_api.h
@@ -613,9 +613,11 @@ static inline void ttm_bo_pin(struct ttm_buffer_object *bo)
 static inline void ttm_bo_unpin(struct ttm_buffer_object *bo)
 {
 	dma_resv_assert_held(bo->base.resv);
-	WARN_ON_ONCE(!bo->pin_count);
 	WARN_ON_ONCE(!kref_read(&bo->kref));
-	--bo->pin_count;
+	if (bo->pin_count)
+		--bo->pin_count;
+	else
+		WARN_ON_ONCE(true);
 }
 
 int ttm_mem_evict_first(struct ttm_bo_device *bdev,
-- 
2.30.1