From: Balbir Singh <balbir@linux.vnet.ibm.com>
To: Li Zefan <lizf@cn.fujitsu.com>
Cc: bharata@linux.vnet.ibm.com, linux-kernel@vger.kernel.org,
Dhaval Giani <dhaval@linux.vnet.ibm.com>,
Paul Menage <menage@google.com>, Ingo Molnar <mingo@elte.hu>,
Peter Zijlstra <a.p.zijlstra@chello.nl>,
KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Subject: Re: [PATCH -tip] cpuacct: Make cpuacct hierarchy walk in cpuacct_charge() safe when rcupreempt is used.
Date: Tue, 17 Mar 2009 18:10:31 +0530 [thread overview]
Message-ID: <20090317124031.GT16897@balbir.in.ibm.com> (raw)
In-Reply-To: <49BF42FB.4030103@cn.fujitsu.com>
* Li Zefan <lizf@cn.fujitsu.com> [2009-03-17 14:28:11]:
> Bharata B Rao wrote:
> > cpuacct: Make cpuacct hierarchy walk in cpuacct_charge() safe when
> > rcupreempt is used.
> >
> > cpuacct_charge() obtains task's ca and does a hierarchy walk upwards.
> > This can race with the task's movement between cgroups. This race
> > can cause an access to freed ca pointer in cpuacct_charge(). This will not
>
> Actually it can also end up access invalid tsk->cgroups. ;)
>
> get tsk->cgroups (cg)
> (move tsk to another cgroup) or (tsk exiting)
> -> kfree(tsk->cgroups)
> get cg->subsys[..]
>
That problem should only occur if we dereference tsk->cgroups
separately and then use that to dereference cg->subsys. Since we use
task_subsys_state() and that is RCU safe, we should be OK.
--
Balbir
next prev parent reply other threads:[~2009-03-17 12:40 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-03-17 6:17 Bharata B Rao
2009-03-17 6:28 ` Li Zefan
2009-03-17 7:36 ` Bharata B Rao
2009-03-17 13:12 ` Balbir Singh
2009-03-17 13:26 ` Peter Zijlstra
2009-03-17 13:59 ` Balbir Singh
2009-03-17 14:04 ` Peter Zijlstra
2009-03-18 3:25 ` Bharata B Rao
2009-03-18 3:54 ` KAMEZAWA Hiroyuki
2009-03-18 4:48 ` Bharata B Rao
2009-03-18 7:08 ` KAMEZAWA Hiroyuki
2009-03-18 8:05 ` Bharata B Rao
2009-03-17 23:59 ` KAMEZAWA Hiroyuki
2009-03-18 3:18 ` Bharata B Rao
2009-03-18 9:36 ` Balbir Singh
2009-03-19 9:20 ` Peter Zijlstra
2009-03-19 9:43 ` Bharata B Rao
2009-03-17 12:40 ` Balbir Singh [this message]
2009-03-18 1:40 ` Li Zefan
2009-03-18 2:59 ` Balbir Singh
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