From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-yh0-f51.google.com (mail-yh0-f51.google.com [209.85.213.51]) by kanga.kvack.org (Postfix) with ESMTP id 6440D6B0031 for ; Wed, 11 Dec 2013 17:23:23 -0500 (EST) Received: by mail-yh0-f51.google.com with SMTP id c41so5611419yho.24 for ; Wed, 11 Dec 2013 14:23:23 -0800 (PST) Received: from mail-yh0-x22e.google.com (mail-yh0-x22e.google.com [2607:f8b0:4002:c01::22e]) by mx.google.com with ESMTPS id v3si19370635yhd.13.2013.12.11.14.23.22 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Wed, 11 Dec 2013 14:23:22 -0800 (PST) Received: by mail-yh0-f46.google.com with SMTP id l109so5624727yhq.5 for ; Wed, 11 Dec 2013 14:23:22 -0800 (PST) Date: Wed, 11 Dec 2013 14:23:18 -0800 (PST) From: David Rientjes Subject: Re: [PATCH] memcg, oom: lock mem_cgroup_print_oom_info In-Reply-To: <1386776545-24916-1-git-send-email-mhocko@suse.cz> Message-ID: References: <1386776545-24916-1-git-send-email-mhocko@suse.cz> 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 , KOSAKI Motohiro , KAMEZAWA Hiroyuki , linux-mm@kvack.org, LKML On Wed, 11 Dec 2013, Michal Hocko wrote: > mem_cgroup_print_oom_info uses a static buffer (memcg_name) to store the > name of the cgroup. This is not safe as pointed out by David Rientjes > because memcg oom is locked only for its hierarchy and nothing prevents > another parallel hierarchy to trigger oom as well and overwrite the > already in-use buffer. > > This patch introduces oom_info_lock hidden inside mem_cgroup_print_oom_info > which is held throughout the function. It make access to memcg_name safe > and as a bonus it also prevents parallel memcg ooms to interleave their > statistics which would make the printed data hard to analyze otherwise. > > Signed-off-by: Michal Hocko Acked-by: David Rientjes > --- > mm/memcontrol.c | 12 +++++++----- > 1 file changed, 7 insertions(+), 5 deletions(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 28c9221b74ea..c72b03bf9679 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -1647,13 +1647,13 @@ static void move_unlock_mem_cgroup(struct mem_cgroup *memcg, > */ > void mem_cgroup_print_oom_info(struct mem_cgroup *memcg, struct task_struct *p) > { > - struct cgroup *task_cgrp; > - struct cgroup *mem_cgrp; > /* > - * Need a buffer in BSS, can't rely on allocations. The code relies > - * on the assumption that OOM is serialized for memory controller. > - * If this assumption is broken, revisit this code. > + * protects memcg_name and makes sure that parallel ooms do not > + * interleave Parallel memcg oom kills can happen in disjoint memcg hierarchies, this just prevents the printing of the statistics from interleaving. I'm not sure if that's clear from this comment. -- 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