From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Glauber Costa <glommer@parallels.com>
Cc: linux-kernel@vger.kernel.org, paul@paulmenage.org,
lizf@cn.fujitsu.com, daniel.lezcano@free.fr,
jbottomley@parallels.com
Subject: Re: [PATCH 04/10] Display /proc/stat information per cgroup
Date: Wed, 05 Oct 2011 14:38:14 +0200 [thread overview]
Message-ID: <1317818294.6766.16.camel@twins> (raw)
In-Reply-To: <4E8C494F.8020804@parallels.com>
On Wed, 2011-10-05 at 16:10 +0400, Glauber Costa wrote:
> On 10/05/2011 12:56 PM, Peter Zijlstra wrote:
> > On Sun, 2011-10-02 at 23:21 +0400, Glauber Costa wrote:
> >> +struct kernel_stat *task_group_kstat(struct task_struct *p)
> >> +{
> >> + struct task_group *tg;
> >> + struct kernel_stat *kstat;
> >> +
> >> + rcu_read_lock();
> >> + tg = task_group(p);
> >> + kstat = tg->cpustat;
> >> + rcu_read_unlock();
> >> + return kstat;
> >> +}
> >
> > Who keeps tg alive and kicking while you poke at its (cpustat) member?
>
> * All calls to this function currently pass current as a parameter
> (Okay, maybe it is too generic and we should pass nothing at all, and
> grab current within it)
> * rcu_read_lock() guarantees that current will exist during this call,
> and task_group won't change. (right?)
The thing I worry about is:
A (pid n) B
kstat = task_group_kstat()
echo n > /cgroup/something-else/pid
rmdir /cgroup/group-that-had-A
<timer interrupt>
RCU complete
<softirq>
kfree(tg) etc..
kstat->foo++; <-- *BOOM*
The only way to avoid someone moving you around is by holding some
cgroup lock, task->alloc_lock, task->pi_lock or the rq->lock where task
runs. Alternatively keep rcu_read_lock() around the entire kstat usage.
next prev parent reply other threads:[~2011-10-05 12:38 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-10-02 19:21 [PATCH 00/10] Per-cgroup /proc/stat information Glauber Costa
2011-10-02 19:21 ` [PATCH 01/10] trivial: initialize root cgroup's sibling list Glauber Costa
2011-10-02 19:21 ` [PATCH 02/10] Change cpustat fields to an array Glauber Costa
2011-10-02 19:21 ` [PATCH 03/10] Move /proc/stat logic inside sched.c Glauber Costa
2011-10-02 19:21 ` [PATCH 04/10] Display /proc/stat information per cgroup Glauber Costa
2011-10-05 8:56 ` Peter Zijlstra
2011-10-05 12:10 ` Glauber Costa
2011-10-05 12:38 ` Peter Zijlstra [this message]
2011-10-05 12:43 ` Glauber Costa
2011-10-05 9:04 ` Peter Zijlstra
2011-10-05 12:11 ` Glauber Costa
2011-10-02 19:21 ` [PATCH 05/10] Make total_forks per-cgroup Glauber Costa
2011-10-05 9:05 ` Peter Zijlstra
2011-10-05 12:12 ` Glauber Costa
2011-10-11 23:45 ` Frederic Weisbecker
2011-10-12 7:35 ` Glauber Costa
2011-10-12 12:59 ` Frederic Weisbecker
2011-10-12 12:59 ` Glauber Costa
2011-10-12 13:03 ` Frederic Weisbecker
2011-10-12 13:03 ` Glauber Costa
2011-10-12 14:03 ` Frederic Weisbecker
2011-10-02 19:21 ` [PATCH 06/10] per-cgroup boot time Glauber Costa
2011-10-02 19:21 ` [PATCH 07/10] Report steal time for cgroup Glauber Costa
2011-10-02 19:21 ` [PATCH 08/10] provide a version of cpuacct statistics inside cpu cgroup Glauber Costa
2011-10-05 9:10 ` Peter Zijlstra
2011-10-05 12:16 ` Glauber Costa
2011-10-02 19:21 ` [PATCH 09/10] provide a version of cpuusage " Glauber Costa
2011-10-05 9:14 ` Peter Zijlstra
2011-10-05 12:17 ` Glauber Costa
2011-10-05 9:46 ` Peter Zijlstra
2011-10-05 12:22 ` Glauber Costa
2011-10-05 12:31 ` Peter Zijlstra
2011-10-05 15:05 ` Glauber Costa
2011-10-02 19:21 ` [PATCH 10/10] Change CPUACCT to default n Glauber Costa
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