From mboxrd@z Thu Jan  1 00:00:00 1970
From: Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
Subject: Re: [PATCH 3/5] cgroup: fix mount failure in a corner case
Date: Fri, 20 Jun 2014 15:10:25 -0400
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To: Li Zefan <lizefan-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>
Cc: LKML <linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, Cgroups <cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>

On Thu, Jun 12, 2014 at 02:32:13PM +0800, Li Zefan wrote:
> @@ -1677,6 +1679,22 @@ static struct dentry *cgroup_mount(struct file_system_type *fs_type,
>  		goto out_unlock;
>  	}
>  
> +	/*
> +	 * If some subsystems have been bound to existing cgroup hierarchies,
> +	 * but those hierachies are being destroyed, let's wait a little bit
> +	 * and retry.
> +	 */
> +	for_each_subsys(ss, i) {
> +		if (!(opts.subsys_mask & (1 << i)))
> +			continue;
> +		if (!percpu_ref_alive(&ss->root->cgrp.self.refcnt)) {

Can't we just do tryget_live() instead and then put before retrying?
It's not exactly a hot path and the operations are dirt cheap anyway.

Thanks.

-- 
tejun