From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f46.google.com (mail-wm0-f46.google.com [74.125.82.46]) by kanga.kvack.org (Postfix) with ESMTP id 1D30F828DF for ; Fri, 15 Jan 2016 15:57:36 -0500 (EST) Received: by mail-wm0-f46.google.com with SMTP id b14so42760101wmb.1 for ; Fri, 15 Jan 2016 12:57:36 -0800 (PST) Received: from gum.cmpxchg.org (gum.cmpxchg.org. [85.214.110.215]) by mx.google.com with ESMTPS id uw9si19973046wjc.111.2016.01.15.12.57.34 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 15 Jan 2016 12:57:34 -0800 (PST) Date: Fri, 15 Jan 2016 15:56:53 -0500 From: Johannes Weiner 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> Sender: owner-linux-mm@kvack.org List-ID: To: Martijn Coenen Cc: Michal Hocko , Vladimir Davydov , cgroups@vger.kernel.org, linux-mm@kvack.org, 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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org