From mboxrd@z Thu Jan 1 00:00:00 1970 From: Johannes Weiner Subject: Re: [PATCH] memcg: Only free spare array when readers are done Date: Fri, 15 Jan 2016 15:56:53 -0500 Message-ID: <20160115205653.GA26524@cmpxchg.org> References: <001a113abaa499606605294b5b17@google.com> Mime-Version: 1.0 Return-path: Content-Disposition: inline In-Reply-To: <001a113abaa499606605294b5b17-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org> Sender: cgroups-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Martijn Coenen Cc: Michal Hocko , Vladimir Davydov , cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.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