linux-kernel - Re: [PATCH v10 4/4] cgroups: implement the PIDs subsystem

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Message-ID: <20150424152613.GB24029@htj.duckdns.org>
Date:	Fri, 24 Apr 2015 11:26:13 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Aleksa Sarai <cyphar@...har.com>
Cc:	lizefan@...wei.com, mingo@...hat.com, peterz@...radead.org,
	richard@....at,
	Frédéric Weisbecker <fweisbec@...il.com>,
	linux-kernel@...r.kernel.org, cgroups@...r.kernel.org
Subject: Re: [PATCH v10 4/4] cgroups: implement the PIDs subsystem

Hello, Aleksa.

On Sat, Apr 25, 2015 at 12:07:34AM +1000, Aleksa Sarai wrote:
> Would something like this suffice?
> 
> struct cgroup_subsys_state *task_get_css(struct task_struct *task, int
> subsys_id) {
>         bool have_ref = false;
>         struct cgroup_subsys_state *css;
> 
>         while(!have_ref) {
>                 rcu_read_lock();
>                 css = task_css(task, subsys_id);
>                 have_ref = !css_tryget(css);
>                 rcu_read_unlock();
>         }
> 
>         return css;
> }

I was thinking why this felt so familiar and realized that I have the
patch pending.

 http://lkml.kernel.org/g/1428350318-8215-8-git-send-email-tj@kernel.org

Please feel free to include it in the patch series.  I'll sort out the
merging later.

> Also, as a side note (in the same vein I guess), does a ref on a
> css_set give you an implicit ref on a css inside that css_set, or are
> those two orthogonal operations?

Yes, it does, but if you're gonna depend on that, please document that.

Thanks.

-- 
tejun
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