drm/i915/ppgtt: Fix ioctl errno for "no such context"

Without this fix the ioctls silently succeeded (but actually did
nothing).

It makes all the code which calls into this function way too confusing.

v2: Fix destroy IOCTL as well

v3: Clarify the other two callers of i915_gem_context_get() to never
check for NULL. (Mika)

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=72903
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Testcase: igt/gem_ctx_exec/basic
[danvet: Fix up the commit message and actually bother to mention the
testcase this fixes.]
Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_gem_context.c

@@ -526,10 +526,16 @@ void i915_gem_context_close(struct drm_device *dev, struct drm_file *file)
 struct i915_hw_context *
 i915_gem_context_get(struct drm_i915_file_private *file_priv, u32 id)
 {
+	struct i915_hw_context *ctx;
+
 	if (!HAS_HW_CONTEXTS(file_priv->dev_priv->dev))
 		return file_priv->private_default_ctx;
 
-	return (struct i915_hw_context *)idr_find(&file_priv->context_idr, id);
+	ctx = (struct i915_hw_context *)idr_find(&file_priv->context_idr, id);
+	if (!ctx)
+		return ERR_PTR(-ENOENT);
+
+	return ctx;
 }
 
 static inline int
@@ -776,9 +782,9 @@ int i915_gem_context_destroy_ioctl(struct drm_device *dev, void *data,
 		return ret;
 
 	ctx = i915_gem_context_get(file_priv, args->ctx_id);
-	if (!ctx) {
+	if (IS_ERR(ctx)) {
 		mutex_unlock(&dev->struct_mutex);
-		return -ENOENT;
+		return PTR_ERR(ctx);
 	}
 
 	idr_remove(&ctx->file_priv->context_idr, ctx->id);

drivers/gpu/drm/i915/i915_gem_execbuffer.c

@@ -904,7 +904,7 @@ i915_gem_validate_context(struct drm_device *dev, struct drm_file *file,
 		return ERR_PTR(-EINVAL);
 
 	ctx = i915_gem_context_get(file->driver_priv, ctx_id);
-	if (IS_ERR_OR_NULL(ctx))
+	if (IS_ERR(ctx))
 		return ctx;
 
 	hs = &ctx->hang_stats;
@@ -1112,7 +1112,7 @@ i915_gem_do_execbuffer(struct drm_device *dev, void *data,
 	}
 
 	ctx = i915_gem_validate_context(dev, file, ring, ctx_id);
-	if (IS_ERR_OR_NULL(ctx)) {
+	if (IS_ERR(ctx)) {
 		mutex_unlock(&dev->struct_mutex);
 		ret = PTR_ERR(ctx);
 		goto pre_mutex_err;