From: Michal Hocko <mhocko@kernel.org>
To: Roman Gushchin <guro@fb.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
linux-mm@kvack.org, Johannes Weiner <hannes@cmpxchg.org>,
linux-kernel@vger.kernel.org, kernel-team@fb.com
Subject: Re: [PATCH] mm: memcontrol: switch to rcu protection in drain_all_stock()
Date: Fri, 2 Aug 2019 10:59:47 +0200 [thread overview]
Message-ID: <20190802085947.GC6461@dhcp22.suse.cz> (raw)
In-Reply-To: <20190802080422.GA6461@dhcp22.suse.cz>
On Fri 02-08-19 10:04:22, Michal Hocko wrote:
> On Thu 01-08-19 16:35:13, Roman Gushchin wrote:
> > Commit 72f0184c8a00 ("mm, memcg: remove hotplug locking from try_charge")
> > introduced css_tryget()/css_put() calls in drain_all_stock(),
> > which are supposed to protect the target memory cgroup from being
> > released during the mem_cgroup_is_descendant() call.
> >
> > However, it's not completely safe. In theory, memcg can go away
> > between reading stock->cached pointer and calling css_tryget().
>
> I have to remember how is this whole thing supposed to work, it's been
> some time since I've looked into that.
OK, I guess I remember now and I do not see how the race is possible.
Stock cache is keeping its memcg alive because it elevates the reference
counting for each cached charge. And that should keep the whole chain up
to the root (of draining) alive, no? Or do I miss something, could you
generate a sequence of events that would lead to use-after-free?
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2019-08-02 8:59 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-01 23:35 [PATCH] mm: memcontrol: switch to rcu protection in drain_all_stock() Roman Gushchin
2019-08-02 3:33 ` Hillf Danton
2019-08-02 8:04 ` Michal Hocko
2019-08-02 8:59 ` Michal Hocko [this message]
2019-08-02 17:00 ` Roman Gushchin
2019-08-02 17:14 ` Michal Hocko
2019-08-02 17:36 ` Roman Gushchin
2019-08-02 16:55 ` Roman Gushchin
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=20190802085947.GC6461@dhcp22.suse.cz \
--to=mhocko@kernel.org \
--cc=akpm@linux-foundation.org \
--cc=guro@fb.com \
--cc=hannes@cmpxchg.org \
--cc=kernel-team@fb.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
/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;
as well as URLs for NNTP newsgroup(s).