On Wed, Nov 28, 2012 at 02:29:08AM -0800, Anton Vorontsov wrote:

+static int mpc_pre_destroy(struct cgroup *cg)
+{
+	struct mpc_state *mpc = cg2mpc(cg);
+	int ret = 0;
+
+	mutex_lock(&mpc->lock);
+
+	if (mpc->eventfd)
+		ret = -EBUSY;

cgroup_rmdir() will unregister all events for you. No need to handle it
here.

+
+	mutex_unlock(&mpc->lock);
+
+	return ret;
+}

+static int mpc_register_level_event(struct cgroup *cg, struct cftype *cft,
+				    struct eventfd_ctx *eventfd,
+				    const char *args)
+{
+	struct mpc_state *mpc = cg2mpc(cg);
+	int i;
+	int ret;
+
+	mutex_lock(&mpc->lock);
+
+	/*
+	 * It's easy to implement multiple thresholds, but so far we don't
+	 * need it.
+	 */
+	if (mpc->eventfd) {
+		ret = -EBUSY;
+		goto out_unlock;
+	}

One user which listen for one threashold per cgroup?
I think it's wrong. It's essensial for API to serve multiple users.

+
+	ret = -EINVAL;
+	for (i = 0; i < VMPRESSURE_NUM_LEVELS; i++) {
+		if (strcmp(vmpressure_str_levels[i], args))
+			continue;
+		mpc->eventfd = eventfd;
+		mpc->thres = i;
+		ret = 0;
+		break;
+	}
+out_unlock:
+	mutex_unlock(&mpc->lock);
+
+	return ret;
+}

-- 
 Kirill A. Shutemov

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