From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pb0-f50.google.com (mail-pb0-f50.google.com [209.85.160.50]) by kanga.kvack.org (Postfix) with ESMTP id AB1C36B0035 for ; Wed, 12 Feb 2014 20:27:38 -0500 (EST) Received: by mail-pb0-f50.google.com with SMTP id rq2so10137983pbb.9 for ; Wed, 12 Feb 2014 17:27:38 -0800 (PST) Received: from mail-pa0-x230.google.com (mail-pa0-x230.google.com [2607:f8b0:400e:c03::230]) by mx.google.com with ESMTPS id vw10si144006pbc.287.2014.02.12.17.27.37 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Wed, 12 Feb 2014 17:27:37 -0800 (PST) Received: by mail-pa0-f48.google.com with SMTP id kx10so9953003pab.21 for ; Wed, 12 Feb 2014 17:27:37 -0800 (PST) Date: Wed, 12 Feb 2014 17:26:46 -0800 (PST) From: Hugh Dickins Subject: [PATCH 1/2] memcg: fix endless loop in __mem_cgroup_iter_next Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: Andrew Morton , Johannes Weiner , Greg Thelen , Tejun Heo , linux-mm@kvack.org, 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; -- 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