From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752305AbaBMB1j (ORCPT ); Wed, 12 Feb 2014 20:27:39 -0500 Received: from mail-pd0-f172.google.com ([209.85.192.172]:56956 "EHLO mail-pd0-f172.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751076AbaBMB1h (ORCPT ); Wed, 12 Feb 2014 20:27:37 -0500 Date: Wed, 12 Feb 2014 17:26:46 -0800 (PST) From: Hugh Dickins X-X-Sender: hugh@eggly.anvils To: Michal Hocko cc: Andrew Morton , Johannes Weiner , Greg Thelen , Tejun Heo , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: [PATCH 1/2] memcg: fix endless loop in __mem_cgroup_iter_next Message-ID: User-Agent: Alpine 2.11 (LSU 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit 0eef615665ed ("memcg: fix css reference leak and endless loop in mem_cgroup_iter") got the interaction with the commit a few before it d8ad30559715 ("mm/memcg: iteration skip memcgs not yet fully initialized") slightly wrong, and we didn't notice at the time. It's elusive, and harder to get than the original, but for a couple of days before rc1, I several times saw a endless loop similar to that supposedly being fixed. This time it was a tighter loop in __mem_cgroup_iter_next(): because we can get here when our root has already been offlined, and the ordering of conditions was such that we then just cycled around forever. Fixes: 0eef615665ed ("memcg: fix css reference leak and endless loop in mem_cgroup_iter") Signed-off-by: Hugh Dickins Cc: stable@vger.kernel.org # 3.12+ --- Of course I'd have preferred to send this before that commit went through to -stable, but priorities kept preempting; I did wonder whether to ask GregKH to delay it, but decided it's not serious enough to trouble him, just go with the flow of stable fixing stable. mm/memcontrol.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) --- 3.14-rc2/mm/memcontrol.c 2014-02-02 18:49:07.897302115 -0800 +++ linux/mm/memcontrol.c 2014-02-12 11:55:02.836035004 -0800 @@ -1127,8 +1127,8 @@ skip_node: * skipping css reference should be safe. */ if (next_css) { - if ((next_css->flags & CSS_ONLINE) && - (next_css == &root->css || css_tryget(next_css))) + if ((next_css == &root->css) || + ((next_css->flags & CSS_ONLINE) && css_tryget(next_css))) return mem_cgroup_from_css(next_css); prev_css = next_css;