[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <20090317124031.GT16897@balbir.in.ibm.com>
Date: Tue, 17 Mar 2009 18:10:31 +0530
From: Balbir Singh <balbir@...ux.vnet.ibm.com>
To: Li Zefan <lizf@...fujitsu.com>
Cc: bharata@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org,
Dhaval Giani <dhaval@...ux.vnet.ibm.com>,
Paul Menage <menage@...gle.com>, Ingo Molnar <mingo@...e.hu>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>,
KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [PATCH -tip] cpuacct: Make cpuacct hierarchy walk in
cpuacct_charge() safe when rcupreempt is used.
* Li Zefan <lizf@...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
--
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/
Powered by blists - more mailing lists