From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753052AbcAOU5g (ORCPT ); Fri, 15 Jan 2016 15:57:36 -0500 Received: from gum.cmpxchg.org ([85.214.110.215]:52994 "EHLO gum.cmpxchg.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751778AbcAOU5e (ORCPT ); Fri, 15 Jan 2016 15:57:34 -0500 Date: Fri, 15 Jan 2016 15:56:53 -0500 From: Johannes Weiner To: Martijn Coenen Cc: Michal Hocko , Vladimir Davydov , cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] memcg: Only free spare array when readers are done Message-ID: <20160115205653.GA26524@cmpxchg.org> References: <001a113abaa499606605294b5b17@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <001a113abaa499606605294b5b17@google.com> User-Agent: Mutt/1.5.24 (2015-08-30) 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: Johannes Weiner