From: Andrew Morton <akpm@linux-foundation.org>
To: Michal Hocko <mhocko@suse.cz>
Cc: Hugh Dickins <hughd@google.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Greg Thelen <gthelen@google.com>,
linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH -mm 2/2] memcg: fix css reference leak and endless loop in mem_cgroup_iter
Date: Tue, 21 Jan 2014 11:42:19 -0800 [thread overview]
Message-ID: <20140121114219.8c34256dfbe7c2470b36ced8@linux-foundation.org> (raw)
In-Reply-To: <1390301143-9541-2-git-send-email-mhocko@suse.cz>
On Tue, 21 Jan 2014 11:45:43 +0100 Michal Hocko <mhocko@suse.cz> wrote:
> 19f39402864e (memcg: simplify mem_cgroup_iter) has reorganized
> mem_cgroup_iter code in order to simplify it. A part of that change was
> dropping an optimization which didn't call css_tryget on the root of
> the walked tree. The patch however didn't change the css_put part in
> mem_cgroup_iter which excludes root.
> This wasn't an issue at the time because __mem_cgroup_iter_next bailed
> out for root early without taking a reference as cgroup iterators
> (css_next_descendant_pre) didn't visit root themselves.
>
> Nevertheless cgroup iterators have been reworked to visit root by
> bd8815a6d802 (cgroup: make css_for_each_descendant() and friends include
> the origin css in the iteration) when the root bypass have been dropped
> in __mem_cgroup_iter_next. This means that css_put is not called for
> root and so css along with mem_cgroup and other cgroup internal object
> tied by css lifetime are never freed.
>
> Fix the issue by reintroducing root check in __mem_cgroup_iter_next
> and do not take css reference for it.
>
> This reference counting magic protects us also from another issue, an
> endless loop reported by Hugh Dickins when reclaim races with root
> removal and css_tryget called by iterator internally would fail. There
> would be no other nodes to visit so __mem_cgroup_iter_next would return
> NULL and mem_cgroup_iter would interpret it as "start looping from root
> again" and so mem_cgroup_iter would loop forever internally.
I grabbed these two patches but I will sit on them for a week or so,
pending review-n-test.
> Cc: stable@vger.kernel.org # mem_leak part 3.12+
What does this mean?
--
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: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
next prev parent reply other threads:[~2014-01-21 19:42 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-01-14 1:50 [PATCH 1/3] mm/memcg: fix last_dead_count memory wastage Hugh Dickins
2014-01-14 1:52 ` [PATCH 2/3] mm/memcg: fix endless iteration in reclaim Hugh Dickins
2014-01-14 13:27 ` Michal Hocko
2014-01-14 13:34 ` Michal Hocko
2014-01-14 14:26 ` Michal Hocko
2014-01-14 20:42 ` Hugh Dickins
2014-01-15 9:58 ` Michal Hocko
2014-01-15 12:17 ` Michal Hocko
2014-01-15 21:24 ` Hugh Dickins
2014-01-16 8:17 ` Michal Hocko
2014-01-16 15:22 ` Michal Hocko
2014-01-16 19:15 ` Hugh Dickins
2014-01-17 15:41 ` Michal Hocko
2014-01-21 5:16 ` Hugh Dickins
2014-01-21 8:34 ` Michal Hocko
2014-01-21 10:45 ` [PATCH -mm 1/2] memcg: fix endless loop caused by mem_cgroup_iter Michal Hocko
2014-01-21 10:45 ` [PATCH -mm 2/2] memcg: fix css reference leak and endless loop in mem_cgroup_iter Michal Hocko
2014-01-21 19:42 ` Andrew Morton [this message]
2014-01-21 21:18 ` Hugh Dickins
2014-01-22 8:27 ` Michal Hocko
2014-01-23 10:42 ` Hugh Dickins
2014-01-23 11:09 ` Michal Hocko
2014-01-23 12:53 ` Hugh Dickins
2014-01-22 8:12 ` Michal Hocko
2014-01-14 1:54 ` [PATCH 3/3] mm/memcg: iteration skip memcgs not yet fully initialized Hugh Dickins
2014-01-14 13:30 ` Michal Hocko
2014-01-14 14:29 ` Tejun Heo
2014-01-15 8:20 ` Michal Hocko
2014-01-15 8:21 ` Michal Hocko
2014-01-14 13:03 ` [PATCH 1/3] mm/memcg: fix last_dead_count memory wastage Michal Hocko
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20140121114219.8c34256dfbe7c2470b36ced8@linux-foundation.org \
--to=akpm@linux-foundation.org \
--cc=gthelen@google.com \
--cc=hannes@cmpxchg.org \
--cc=hughd@google.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=mhocko@suse.cz \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox