[PATCH] drm/msm: move submit fence wait out of struct_mutex

[Rob Clark]

Probably a symptom of needing finer grained locking, but if we wait on
the incoming fence-fd (which could come from a different context) while
holding struct_mutex, that blocks retire_worker so gpu fences cannot get
scheduled.

This causes a problem if userspace manages to get more than a frame
ahead, leaving the atomic-commit worker blocked waiting on fences that
cannot be signaled because submit is blocked waiting for a fence
signalled from vblank (after the atomic commit which is blocked).

If we start having multiple fence ctxs for the gpu, submit_fence_sync()
would probably need to move outside of struct_mutex as well.

Signed-off-by: Rob Clark <robdclark at gmail.com>
---
 drivers/gpu/drm/msm/msm_gem_submit.c | 39 +++++++++++++++++-------------------
 1 file changed, 18 insertions(+), 21 deletions(-)

diff --git a/drivers/gpu/drm/msm/msm_gem_submit.c b/drivers/gpu/drm/msm/msm_gem_submit.c
index 1172fe7..1c545eb 100644
--- a/drivers/gpu/drm/msm/msm_gem_submit.c
+++ b/drivers/gpu/drm/msm/msm_gem_submit.c
@@ -404,6 +404,24 @@ int msm_ioctl_gem_submit(struct drm_device *dev, void *data,
 	if (MSM_PIPE_FLAGS(args->flags) & ~MSM_SUBMIT_FLAGS)
 		return -EINVAL;
 
+	if (args->flags & MSM_SUBMIT_FENCE_FD_IN) {
+		in_fence = sync_file_get_fence(args->fence_fd);
+
+		if (!in_fence)
+			return -EINVAL;
+
+		/* TODO if we get an array-fence due to userspace merging multiple
+		 * fences, we need a way to determine if all the backing fences
+		 * are from our own context..
+		 */
+
+		if (in_fence->context != gpu->fctx->context) {
+			ret = dma_fence_wait(in_fence, true);
+			if (ret)
+				return ret;
+		}
+	}
+
 	ret = mutex_lock_interruptible(&dev->struct_mutex);
 	if (ret)
 		return ret;
@@ -431,27 +449,6 @@ int msm_ioctl_gem_submit(struct drm_device *dev, void *data,
 	if (ret)
 		goto out;
 
-	if (args->flags & MSM_SUBMIT_FENCE_FD_IN) {
-		in_fence = sync_file_get_fence(args->fence_fd);
-
-		if (!in_fence) {
-			ret = -EINVAL;
-			goto out;
-		}
-
-		/* TODO if we get an array-fence due to userspace merging multiple
-		 * fences, we need a way to determine if all the backing fences
-		 * are from our own context..
-		 */
-
-		if (in_fence->context != gpu->fctx->context) {
-			ret = dma_fence_wait(in_fence, true);
-			if (ret)
-				goto out;
-		}
-
-	}
-
 	if (!(args->fence & MSM_SUBMIT_NO_IMPLICIT)) {
 		ret = submit_fence_sync(submit);
 		if (ret)
-- 
2.9.3