drm/v3d: Take a lock across GPU scheduler job creation and queuing.

Between creation and queueing of a job, you need to prevent any other
job from being created and queued.  Otherwise the scheduler's fences
may be signaled out of seqno order.

v2: move mutex unlock to the error label.

Signed-off-by: Eric Anholt <eric@anholt.net>
Fixes: 57692c94dcbe ("drm/v3d: Introduce a new DRM driver for Broadcom V3D V3.x+")
Link: https://patchwork.freedesktop.org/patch/msgid/20180606174851.12433-1-eric@anholt.net
Reviewed-by: Lucas Stach <l.stach@pengutronix.de>

drivers/gpu/drm/v3d/v3d_drv.h

@@ -85,6 +85,11 @@ struct v3d_dev {
 	 */
 	struct mutex reset_lock;
 
+	/* Lock taken when creating and pushing the GPU scheduler
+	 * jobs, to keep the sched-fence seqnos in order.
+	 */
+	struct mutex sched_lock;
+
 	struct {
 		u32 num_allocated;
 		u32 pages_allocated;

drivers/gpu/drm/v3d/v3d_gem.c

@@ -550,6 +550,7 @@ v3d_submit_cl_ioctl(struct drm_device *dev, void *data,
 	if (ret)
 		goto fail;
 
+	mutex_lock(&v3d->sched_lock);
 	if (exec->bin.start != exec->bin.end) {
 		ret = drm_sched_job_init(&exec->bin.base,
 					 &v3d->queue[V3D_BIN].sched,
@@ -576,6 +577,7 @@ v3d_submit_cl_ioctl(struct drm_device *dev, void *data,
 	kref_get(&exec->refcount); /* put by scheduler job completion */
 	drm_sched_entity_push_job(&exec->render.base,
 				  &v3d_priv->sched_entity[V3D_RENDER]);
+	mutex_unlock(&v3d->sched_lock);
 
 	v3d_attach_object_fences(exec);
 
@@ -594,6 +596,7 @@ v3d_submit_cl_ioctl(struct drm_device *dev, void *data,
 	return 0;
 
 fail_unreserve:
+	mutex_unlock(&v3d->sched_lock);
 	v3d_unlock_bo_reservations(dev, exec, &acquire_ctx);
 fail:
 	v3d_exec_put(exec);
@@ -615,6 +618,7 @@ v3d_gem_init(struct drm_device *dev)
 	spin_lock_init(&v3d->job_lock);
 	mutex_init(&v3d->bo_lock);
 	mutex_init(&v3d->reset_lock);
+	mutex_init(&v3d->sched_lock);
 
 	/* Note: We don't allocate address 0.  Various bits of HW
 	 * treat 0 as special, such as the occlusion query counters