openwrt/target/linux/brcm2708/patches-4.4/0096-drm-vc4-Drop-struct_mutex-around-CL-validation.patch

From 08d3b4a8535a142d79c30fe6a558ac8c97de11f1 Mon Sep 17 00:00:00 2001
From: Eric Anholt <eric@anholt.net>
Date: Mon, 19 Oct 2015 08:44:35 -0700
Subject: [PATCH] drm/vc4: Drop struct_mutex around CL validation.

We were using it so that we could make sure that shader validation
state didn't change while we were validating, but now shader
validation state is immutable.  The bcl/rcl generation doesn't do any
other BO dereferencing, and seems to have no other global state
dependency not covered by job_lock / bo_lock.  We only need to hold
struct_mutex for object unreferencing.

Fixes a lock order reversal between mmap_sem and struct_mutex.

Signed-off-by: Eric Anholt <eric@anholt.net>
---
 drivers/gpu/drm/vc4/vc4_gem.c | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

--- a/drivers/gpu/drm/vc4/vc4_gem.c
+++ b/drivers/gpu/drm/vc4/vc4_gem.c
@@ -439,10 +439,12 @@ fail:
 }
 
 static void
-vc4_complete_exec(struct vc4_exec_info *exec)
+vc4_complete_exec(struct drm_device *dev, struct vc4_exec_info *exec)
 {
 	unsigned i;
 
+	/* Need the struct lock for drm_gem_object_unreference(). */
+	mutex_lock(&dev->struct_mutex);
 	if (exec->bo) {
 		for (i = 0; i < exec->bo_count; i++)
 			drm_gem_object_unreference(&exec->bo[i].bo->base);
@@ -455,6 +457,7 @@ vc4_complete_exec(struct vc4_exec_info *
 		list_del(&bo->unref_head);
 		drm_gem_object_unreference(&bo->base.base);
 	}
+	mutex_unlock(&dev->struct_mutex);
 
 	kfree(exec);
 }
@@ -473,7 +476,7 @@ vc4_job_handle_completed(struct vc4_dev
 		list_del(&exec->head);
 
 		spin_unlock_irqrestore(&vc4->job_lock, irqflags);
-		vc4_complete_exec(exec);
+		vc4_complete_exec(vc4->dev, exec);
 		spin_lock_irqsave(&vc4->job_lock, irqflags);
 	}
 
@@ -525,12 +528,8 @@ vc4_job_done_work(struct work_struct *wo
 {
 	struct vc4_dev *vc4 =
 		container_of(work, struct vc4_dev, job_done_work);
-	struct drm_device *dev = vc4->dev;
 
-	/* Need the struct lock for drm_gem_object_unreference(). */
-	mutex_lock(&dev->struct_mutex);
 	vc4_job_handle_completed(vc4);
-	mutex_unlock(&dev->struct_mutex);
 }
 
 static int
@@ -639,7 +638,7 @@ vc4_submit_cl_ioctl(struct drm_device *d
 	return 0;
 
 fail:
-	vc4_complete_exec(exec);
+	vc4_complete_exec(vc4->dev, exec);
 
 	return ret;
 }