From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751431AbaJOSbx (ORCPT ); Wed, 15 Oct 2014 14:31:53 -0400 Received: from gum.cmpxchg.org ([85.214.110.215]:41969 "EHLO gum.cmpxchg.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750721AbaJOSbw (ORCPT ); Wed, 15 Oct 2014 14:31:52 -0400 Date: Wed, 15 Oct 2014 14:31:37 -0400 From: Johannes Weiner To: Michal Hocko Cc: Andrew Morton , Vladimir Davydov , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [patch 1/5] mm: memcontrol: convert reclaim iterator to simple css refcounting Message-ID: <20141015183137.GA6442@phnom.home.cmpxchg.org> References: <1413303637-23862-1-git-send-email-hannes@cmpxchg.org> <1413303637-23862-2-git-send-email-hannes@cmpxchg.org> <20141015150256.GF23547@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20141015150256.GF23547@dhcp22.suse.cz> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Oct 15, 2014 at 05:02:56PM +0200, Michal Hocko wrote: > On Tue 14-10-14 12:20:33, Johannes Weiner wrote: > > The memcg reclaim iterators use a complicated weak reference scheme to > > prevent pinning cgroups indefinitely in the absence of memory pressure. > > > > However, during the ongoing cgroup core rework, css lifetime has been > > decoupled such that a pinned css no longer interferes with removal of > > the user-visible cgroup, and all this complexity is now unnecessary. > > > > Signed-off-by: Johannes Weiner > > --- > > mm/memcontrol.c | 250 +++++++++++++++++--------------------------------------- > > 1 file changed, 76 insertions(+), 174 deletions(-) > > > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > > index b62972c80055..67dabe8b0aa6 100644 > > --- a/mm/memcontrol.c > > +++ b/mm/memcontrol.c > [...] > > + do { > > + pos = ACCESS_ONCE(iter->position); > > + /* > > + * A racing update may change the position and > > + * put the last reference, hence css_tryget(), > > + * or retry to see the updated position. > > + */ > > + } while (pos && !css_tryget(&pos->css)); > > + } > [...] > > + if (reclaim) { > > + if (cmpxchg(&iter->position, pos, memcg) == pos && memcg) > > + css_get(&memcg->css); > > + > > + if (pos) > > + css_put(&pos->css); > > This looks like a reference leak. css_put pairs with the above > css_tryget but no css_put pairs with css_get for the cached one. We > need: > --- > From 2810937ec6c16afc0bf924e761ff8305bd478a42 Mon Sep 17 00:00:00 2001 > From: Michal Hocko > Date: Wed, 15 Oct 2014 16:26:22 +0200 > Subject: [PATCH] > mm-memcontrol-convert-reclaim-iterator-to-simple-css-refcounting-fix > > Make sure that the cached reference is always released. > > Signed-off-by: Michal Hocko You're right, thanks for catching that. Acked-by: Johannes Weiner