linux-kernel - Re: [PATCH 1/2] memcg: reparent charges of children before processing parent

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Wed, 12 Feb 2014 19:25:38 -0500
From:	Tejun Heo <tj@...nel.org>
To:	Hugh Dickins <hughd@...gle.com>
Cc:	Michal Hocko <mhocko@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>,
	Filipe Brandenburger <filbranden@...gle.com>,
	Li Zefan <lizefan@...wei.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Greg Thelen <gthelen@...gle.com>,
	Michel Lespinasse <walken@...gle.com>,
	Markus Blank-Burian <burian@...nster.de>,
	Shawn Bohrer <shawn.bohrer@...il.com>, cgroups@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 1/2] memcg: reparent charges of children before
 processing parent

Hello,

On Wed, Feb 12, 2014 at 03:03:31PM -0800, Hugh Dickins wrote:
> From: Filipe Brandenburger <filbranden@...gle.com>
> 
> Sometimes the cleanup after memcg hierarchy testing gets stuck in
> mem_cgroup_reparent_charges(), unable to bring non-kmem usage down to 0.
> 
> There may turn out to be several causes, but a major cause is this: the
> workitem to offline parent can get run before workitem to offline child;
> parent's mem_cgroup_reparent_charges() circles around waiting for the
> child's pages to be reparented to its lrus, but it's holding cgroup_mutex
> which prevents the child from reaching its mem_cgroup_reparent_charges().
> 
> Further testing showed that an ordered workqueue for cgroup_destroy_wq
> is not always good enough: percpu_ref_kill_and_confirm's call_rcu_sched
> stage on the way can mess up the order before reaching the workqueue.
> 
> Instead, when offlining a memcg, call mem_cgroup_reparent_charges() on
> all its children (and grandchildren, in the correct order) to have their
> charges reparented first.
> 
> Fixes: e5fca243abae ("cgroup: use a dedicated workqueue for cgroup destruction")
> Signed-off-by: Filipe Brandenburger <filbranden@...gle.com>
> Signed-off-by: Hugh Dickins <hughd@...gle.com>
> Cc: stable@...r.kernel.org # v3.10+ (but will need extra care)
> ---
> Or, you may prefer my alternative cgroup.c approach in 2/2:
> there's no need for both.  Please note that neither of these patches
> attempts to handle the unlikely case of racy charges made to child
> after its offline, but parent's offline coming before child's free:
> mem_cgroup_css_free()'s backstop call to mem_cgroup_reparent_charges()
> cannot help in that case, with or without these patches.  Fixing that
> would have to be a separate effort - Michal's?

I've changed my mind several times now but I think it'd be a better
idea to stick to this patch, at least for now.  This one is easier for
-stable backport and it looks like the requirements for ordering
->css_offline() might go away depending on how reparenting changes
work out.

 Reviewed-by: Tejun Heo <tj@...nel.org>

Michal, Johannes, can you guys please ack this one if you guys agree?

Thanks.

-- 
tejun
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/