drm/i915/gvt: fix lock not released bug for dispatch_workload() err path

Need to be careful to release struct_mutext when request alloc
failed and take consistent handling for return status as with
normal go out path. Ensure to check correct workload request in
complete path too.

v2: Add Fixes note

Fixes: 90d27a1b ("drm/i915/gvt: fix deadlock in workload_thread")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Pei Zhang <pei.zhang@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>

drivers/gpu/drm/i915/gvt/scheduler.c

@@ -177,8 +177,8 @@ static int dispatch_workload(struct intel_vgpu_workload *workload)
 	rq = i915_gem_request_alloc(dev_priv->engine[ring_id], shadow_ctx);
 	if (IS_ERR(rq)) {
 		gvt_err("fail to allocate gem request\n");
-		workload->status = PTR_ERR(rq);
-		return workload->status;
+		ret = PTR_ERR(rq);
+		goto out;
 	}
 
 	gvt_dbg_sched("ring id %d get i915 gem request %p\n", ring_id, rq);
@@ -212,6 +212,7 @@ static int dispatch_workload(struct intel_vgpu_workload *workload)
 	if (ret)
 		workload->status = ret;
 
+	if (!IS_ERR_OR_NULL(rq))
 		i915_add_request_no_flush(rq);
 	mutex_unlock(&dev_priv->drm.struct_mutex);
 	return ret;
@@ -460,6 +461,7 @@ static int workload_thread(void *priv)
 
 		complete_current_workload(gvt, ring_id);
 
+		if (workload->req)
 			i915_gem_request_put(fetch_and_zero(&workload->req));
 
 		if (need_force_wake)