drm/i915: Fix error checking/locking in perf/lookup_context()

1acfc104 missed to convert this one caller to be lockless. The side
effect of that was that the error check in lookup_context() became
incorrect. Convert now this caller too.

Fixes: 1acfc104 ("drm/i915: Enable rcu-only context lookups")
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170714151242.517-1-imre.deak@intel.com

drivers/gpu/drm/i915/i915_perf.c

@@ -2483,27 +2483,6 @@ static const struct file_operations fops = {
 };
 
 
-static struct i915_gem_context *
-lookup_context(struct drm_i915_private *dev_priv,
-	       struct drm_i915_file_private *file_priv,
-	       u32 ctx_user_handle)
-{
-	struct i915_gem_context *ctx;
-	int ret;
-
-	ret = i915_mutex_lock_interruptible(&dev_priv->drm);
-	if (ret)
-		return ERR_PTR(ret);
-
-	ctx = i915_gem_context_lookup(file_priv, ctx_user_handle);
-	if (!IS_ERR(ctx))
-		i915_gem_context_get(ctx);
-
-	mutex_unlock(&dev_priv->drm.struct_mutex);
-
-	return ctx;
-}
-
 /**
  * i915_perf_open_ioctl_locked - DRM ioctl() for userspace to open a stream FD
  * @dev_priv: i915 device instance
@@ -2545,12 +2524,11 @@ i915_perf_open_ioctl_locked(struct drm_i915_private *dev_priv,
 		u32 ctx_handle = props->ctx_handle;
 		struct drm_i915_file_private *file_priv = file->driver_priv;
 
-		specific_ctx = lookup_context(dev_priv, file_priv, ctx_handle);
-		if (IS_ERR(specific_ctx)) {
-			ret = PTR_ERR(specific_ctx);
-			if (ret != -EINTR)
+		specific_ctx = i915_gem_context_lookup(file_priv, ctx_handle);
+		if (!specific_ctx) {
 			DRM_DEBUG("Failed to look up context with ID %u for opening perf stream\n",
 				  ctx_handle);
+			ret = -ENOENT;
 			goto err;
 		}
 	}