From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ea0-f176.google.com (mail-ea0-f176.google.com [209.85.215.176]) by kanga.kvack.org (Postfix) with ESMTP id 7193E6B0035 for ; Wed, 15 Jan 2014 03:21:40 -0500 (EST) Received: by mail-ea0-f176.google.com with SMTP id h14so273249eaj.21 for ; Wed, 15 Jan 2014 00:21:39 -0800 (PST) Received: from mx2.suse.de (cantor2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id e2si6338340eeg.30.2014.01.15.00.21.39 for (version=TLSv1 cipher=RC4-SHA bits=128/128); Wed, 15 Jan 2014 00:21:39 -0800 (PST) Date: Wed, 15 Jan 2014 09:21:38 +0100 From: Michal Hocko Subject: Re: [PATCH 3/3] mm/memcg: iteration skip memcgs not yet fully initialized Message-ID: <20140115082138.GB8782@dhcp22.suse.cz> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Hugh Dickins Cc: Johannes Weiner , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org On Mon 13-01-14 17:54:04, Hugh Dickins wrote: > It is surprising that the mem_cgroup iterator can return memcgs which > have not yet been fully initialized. By accident (or trial and error?) > this appears not to present an actual problem; but it may be better to > prevent such surprises, by skipping memcgs not yet online. > > Signed-off-by: Hugh Dickins This makes a perfect sense now after Tejun pointed out that I was wrong assuming css_online is called before cgroup is made visible. Acked-by: Michal Hocko > --- > Decide for yourself whether to take this or not. I spent quite a while > digging into a mysterious "trying to register non-static key" issue from > lockdep, which originated from the iterator returning a vmalloc'ed memcg > a moment before the res_counter_init()s had done their spin_lock_init()s. > But the backtrace was an odd one of our own mis-devising, not a charge or > reclaim or stats trace, so probably it's never been a problem for vanilla. > > mm/memcontrol.c | 6 ++---- > 1 file changed, 2 insertions(+), 4 deletions(-) > > --- mmotm/mm/memcontrol.c 2014-01-10 18:25:02.236448954 -0800 > +++ linux/mm/memcontrol.c 2014-01-12 22:21:10.700570471 -0800 > @@ -1119,10 +1119,8 @@ skip_node: > * protected by css_get and the tree walk is rcu safe. > */ > if (next_css) { > - struct mem_cgroup *mem = mem_cgroup_from_css(next_css); > - > - if (css_tryget(&mem->css)) > - return mem; > + if ((next_css->flags & CSS_ONLINE) && css_tryget(next_css)) > + return mem_cgroup_from_css(next_css); > else { > prev_css = next_css; > goto skip_node; -- Michal Hocko SUSE Labs -- 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