drm/msm: Protect obj->active_count under obj lock

Previously we only held obj lock in the _active_get() path, and relied
on atomic_dec_return() to not be racy in the _active_put() path where
obj lock was not held.

But this is a false sense of security.  Unlike obj lifetime refcnt,
where you do not expect to *increase* the refcnt after the last put
(which would mean that something has gone horribly wrong with the
object liveness reference counting), the active_count can increase
again from zero.  Racing _active_put()s and _active_get()s could leave
the obj on the wrong mm list.

But in the retire path, immediately after the _active_put(), the
_unpin_iova() would acquire obj lock.  So just move the locking earlier
and rely on that to protect obj->active_count.

Fixes: c5c1643cef7a ("drm/msm: Drop struct_mutex from the retire path")
Signed-off-by: Rob Clark <robdclark@chromium.org>

1 files changed, 6 insertions, 4 deletions

diff --git a/drivers/gpu/drm/msm/msm_gpu.c b/drivers/gpu/drm/msm/msm_gpu.c
index dfa3b5ad2099..ab7c167b0623 100644
--- a/drivers/gpu/drm/msm/msm_gpu.c
+++ b/drivers/gpu/drm/msm/msm_gpu.c
@@ -719,11 +719,13 @@ static void retire_submit(struct msm_gpu *gpu, struct msm_ringbuffer *ring,
 		stats->alwayson_start, stats->alwayson_end);
 
 	for (i = 0; i < submit->nr_bos; i++) {
-		struct msm_gem_object *msm_obj = submit->bos[i].obj;
+		struct drm_gem_object *obj = &submit->bos[i].obj->base;
 
-		msm_gem_active_put(&msm_obj->base);
-		msm_gem_unpin_iova(&msm_obj->base, submit->aspace);
-		drm_gem_object_put(&msm_obj->base);
+		msm_gem_lock(obj);
+		msm_gem_active_put(obj);
+		msm_gem_unpin_iova_locked(obj, submit->aspace);
+		msm_gem_unlock(obj);
+		drm_gem_object_put(obj);
 	}
 
 	pm_runtime_mark_last_busy(&gpu->pdev->dev);