netdev - Re: [PATCH 2/3] don't take cgroup

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Message-ID: <20120419225704.GE10553@google.com>
Date:	Thu, 19 Apr 2012 15:57:04 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Glauber Costa <glommer@...allels.com>
Cc:	netdev@...r.kernel.org, cgroups@...r.kernel.org,
	Li Zefan <lizefan@...wei.com>, kamezawa.hiroyu@...fujitsu.com,
	David Miller <davem@...emloft.net>, devel@...nvz.org,
	Vivek Goyal <vgoyal@...hat.com>
Subject: Re: [PATCH 2/3] don't take cgroup_mutex in destroy()

On Thu, Apr 19, 2012 at 07:49:17PM -0300, Glauber Costa wrote:
> Most of the destroy functions are only doing very simple things
> like freeing memory.
> 
> The ones who goes through lists and such, already use its own
> locking for those.
> 
> * The cgroup itself won't go away until we free it, (after destroy)
> * The parent won't go away because we hold a reference count
> * There are no more tasks in the cgroup, and the cgroup is declared
>   dead (cgroup_is_removed() == true)
> 
> For the blk-cgroup and the cpusets, I got the impression that the mutex
> is still necessary.
> 
> For those, I grabbed it from within the destroy function itself.
> 
> If the maintainer for those subsystems consider it safe to remove
> it, we can discuss it separately.

I really don't like cgroup_lock() usage spreading more.  It's
something which should be contained in cgroup.c proper.  I looked at
the existing users a while ago and they seemed to be compensating
deficencies in API, so, if at all possible, let's not spread the
disease.

Thanks.

-- 
tejun
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