[bug report] drm/i915/gvt: fix deadlock in workload_thread

[Dan Carpenter <dan.carpenter@oracle.com>]

Hello Pei Zhang,

The patch 90d27a1b180e: "drm/i915/gvt: fix deadlock in
workload_thread" from Nov 14, 2016, leads to the following static
checker warning:

	drivers/gpu/drm/i915/gvt/scheduler.c:217 dispatch_workload()
	warn: inconsistent returns 'mutex:&dev_priv->drm.struct_mutex'.

drivers/gpu/drm/i915/gvt/scheduler.c
   161  static int dispatch_workload(struct intel_vgpu_workload *workload)
   162  {
   163          int ring_id = workload->ring_id;
   164          struct i915_gem_context *shadow_ctx = workload->vgpu->shadow_ctx;
   165          struct drm_i915_private *dev_priv = workload->vgpu->gvt->dev_priv;
   166          struct drm_i915_gem_request *rq;
   167          int ret;
   168  
   169          gvt_dbg_sched("ring id %d prepare to dispatch workload %p\n",
   170                  ring_id, workload);
   171  
   172          shadow_ctx->desc_template = workload->ctx_desc.addressing_mode <<
   173                                      GEN8_CTX_ADDRESSING_MODE_SHIFT;
   174  
   175          mutex_lock(&dev_priv->drm.struct_mutex);
   176  
   177          rq = i915_gem_request_alloc(dev_priv->engine[ring_id], shadow_ctx);
   178          if (IS_ERR(rq)) {
   179                  gvt_err("fail to allocate gem request\n");
   180                  workload->status = PTR_ERR(rq);
   181                  return workload->status;

We're holding the lock here, which is obviously a bug.  But also should
we goto out?  I always thought that functions with an "out" label were
future proof?

   182          }
   183  
   184          gvt_dbg_sched("ring id %d get i915 gem request %p\n", ring_id, rq);
   185  
   186          workload->req = i915_gem_request_get(rq);
   187  
   188          ret = intel_gvt_scan_and_shadow_workload(workload);
   189          if (ret)
   190                  goto out;
   191  
   192          ret = intel_gvt_scan_and_shadow_wa_ctx(&workload->wa_ctx);
   193          if (ret)
   194                  goto out;
   195  

regards,
dan carpenter
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