linux-kernel - Re: 3.13-rc breaks MEMCG

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Message-ID: <20131217122926.GC29989@htj.dyndns.org>
Date:	Tue, 17 Dec 2013 07:29:26 -0500
From:	Tejun Heo <tj@...nel.org>
To:	Li Zefan <lizefan@...wei.com>
Cc:	Hugh Dickins <hughd@...gle.com>, Michal Hocko <mhocko@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	linux-mm@...ck.org, cgroups@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: 3.13-rc breaks MEMCG_SWAP

Hello, Li.

On Tue, Dec 17, 2013 at 11:13:39AM +0800, Li Zefan wrote:
> diff --git a/kernel/cgroup.c b/kernel/cgroup.c
> index c36d906..769b5bb 100644
> --- a/kernel/cgroup.c
> +++ b/kernel/cgroup.c
> @@ -868,6 +868,15 @@ static void cgroup_diput(struct dentry *dentry, struct inode *inode)
>  		struct cgroup *cgrp = dentry->d_fsdata;
>  
>  		BUG_ON(!(cgroup_is_dead(cgrp)));
> +
> +		/*
> +		 * We should remove the cgroup object from idr before its
> +		 * grace period starts, so we won't be looking up a cgroup
> +		 * while the cgroup is being freed.
> +		 */

Let's remove this comment and instead comment that this is to be made
per-css.  I mixed up the lifetime rules of the cgroup and css and
thought css_from_id() should fail once css is confirmed to be offline,
so the above comment.  It looks like we'll eventually have to move
cgrp->id to css->id (just simple per-ss idr) as the two objects'
lifetime rules will be completely separate.  Other than that, looks
good to me.

Thanks.

-- 
tejun
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