From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757495AbcAOLQk (ORCPT ); Fri, 15 Jan 2016 06:16:40 -0500 Received: from relay.parallels.com ([195.214.232.42]:56902 "EHLO relay.parallels.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755441AbcAOLQi (ORCPT ); Fri, 15 Jan 2016 06:16:38 -0500 Date: Fri, 15 Jan 2016 14:16:23 +0300 From: Vladimir Davydov To: Martijn Coenen CC: Johannes Weiner , Michal Hocko , , , Subject: Re: [PATCH] memcg: Only free spare array when readers are done Message-ID: <20160115111623.GA13257@esperanza> References: <001a113abaa499606605294b5b17@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <001a113abaa499606605294b5b17@google.com> X-ClientProxiedBy: US-EXCH.sw.swsoft.com (10.255.249.47) To MSK-EXCH1.sw.swsoft.com (10.67.48.55) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jan 14, 2016 at 02:33:52PM +0100, Martijn Coenen wrote: > A spare array holding mem cgroup threshold events is kept around > to make sure we can always safely deregister an event and have an > array to store the new set of events in. > > In the scenario where we're going from 1 to 0 registered events, the > pointer to the primary array containing 1 event is copied to the spare > slot, and then the spare slot is freed because no events are left. > However, it is freed before calling synchronize_rcu(), which means > readers may still be accessing threshold->primary after it is freed. > > Fixed by only freeing after synchronize_rcu(). > > Signed-off-by: Martijn Coenen Acked-by: Vladimir Davydov