From: Vladimir Davydov <vdavydov@parallels.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>,
Andrew Morton <akpm@linux-foundation.org>,
Tejun Heo <tj@kernel.org>, Oleg Nesterov <oleg@redhat.com>,
Greg Thelen <gthelen@google.com>,
KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 8/8] memcg: get rid of mem_cgroup_from_task
Date: Thu, 9 Jul 2015 17:32:47 +0300 [thread overview]
Message-ID: <20150709143246.GL2436@esperanza> (raw)
In-Reply-To: <20150709141320.GH13872@dhcp22.suse.cz>
On Thu, Jul 09, 2015 at 04:13:21PM +0200, Michal Hocko wrote:
> On Wed 08-07-15 20:43:31, Vladimir Davydov wrote:
> > On Wed, Jul 08, 2015 at 02:27:52PM +0200, Michal Hocko wrote:
> [...]
> > > @@ -1091,12 +1079,14 @@ bool task_in_mem_cgroup(struct task_struct *task, struct mem_cgroup *memcg)
> > > task_unlock(p);
> > > } else {
> > > /*
> > > - * All threads may have already detached their mm's, but the oom
> > > - * killer still needs to detect if they have already been oom
> > > - * killed to prevent needlessly killing additional tasks.
> > > + * All threads have already detached their mm's but we should
> > > + * still be able to at least guess the original memcg from the
> > > + * task_css. These two will match most of the time but there are
> > > + * corner cases where task->mm and task_css refer to a different
> > > + * cgroups.
> > > */
> > > rcu_read_lock();
> > > - task_memcg = mem_cgroup_from_task(task);
> > > + task_memcg = mem_cgroup_from_css(task_css(task, memory_cgrp_id));
> > > css_get(&task_memcg->css);
> >
> > I wonder why it's safe to call css_get here.
>
> What do you mean by safe? Memcg cannot go away because we are under rcu
> lock.
No, it can't, but css->refcnt can reach zero while we are here, can't
it? If it happens, css->refcnt.release will be called twice, which will
have very bad consequences. I think it's OK to call css_tryget{_online}
from an RCU read-side section, but not css_get. Am I missing something?
Thanks,
Vladimir
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next prev parent reply other threads:[~2015-07-09 14:33 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-07-08 12:27 [PATCH 0/8 -v3] memcg cleanups + get rid of mm_struct::owner Michal Hocko
2015-07-08 12:27 ` [PATCH 1/8] memcg: export struct mem_cgroup Michal Hocko
2015-07-08 15:39 ` Vladimir Davydov
2015-07-09 11:22 ` Michal Hocko
2015-07-09 11:51 ` Vladimir Davydov
2015-07-08 12:27 ` [PATCH 2/8] memcg: get rid of mem_cgroup_root_css for !CONFIG_MEMCG Michal Hocko
2015-07-08 15:41 ` Vladimir Davydov
2015-07-08 12:27 ` [PATCH 3/8] memcg: get rid of extern for functions in memcontrol.h Michal Hocko
2015-07-08 15:43 ` Vladimir Davydov
2015-07-08 12:27 ` [PATCH 4/8] memcg, mm: move mem_cgroup_select_victim_node into vmscan Michal Hocko
2015-07-08 16:01 ` Vladimir Davydov
2015-07-09 12:08 ` Michal Hocko
2015-07-08 12:27 ` [PATCH 5/8] memcg: restructure mem_cgroup_can_attach() Michal Hocko
2015-07-08 16:05 ` Vladimir Davydov
2015-07-08 12:27 ` [PATCH 6/8] memcg, tcp_kmem: check for cg_proto in sock_update_memcg Michal Hocko
2015-07-08 16:11 ` Vladimir Davydov
2015-07-08 12:27 ` [PATCH 7/8] memcg: get rid of mm_struct::owner Michal Hocko
2015-07-08 17:32 ` Vladimir Davydov
2015-07-09 14:09 ` Michal Hocko
2015-07-10 7:54 ` Vladimir Davydov
2015-07-10 12:45 ` Michal Hocko
2015-07-11 7:09 ` Vladimir Davydov
2015-07-14 15:32 ` Michal Hocko
2015-07-10 14:05 ` Michal Hocko
2015-07-14 15:18 ` Michal Hocko
2015-07-29 11:58 ` Michal Hocko
2015-07-29 13:14 ` Johannes Weiner
2015-07-29 15:05 ` Michal Hocko
2015-07-29 16:42 ` Johannes Weiner
2015-07-08 12:27 ` [PATCH 8/8] memcg: get rid of mem_cgroup_from_task Michal Hocko
2015-07-08 17:43 ` Vladimir Davydov
2015-07-09 14:13 ` Michal Hocko
2015-07-09 14:32 ` Vladimir Davydov [this message]
2015-07-09 16:33 ` Michal Hocko
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