linux-kernel - Re: [PATCH v1 2/3] cgroup: allow for unprivileged subtree management

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Message-ID: <20160720154557.GF4574@htj.duckdns.org>
Date:	Wed, 20 Jul 2016 11:45:57 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Aleksa Sarai <asarai@...e.de>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Li Zefan <lizefan@...wei.com>,
	Johannes Weiner <hannes@...xchg.org>,
	"Serge E. Hallyn" <serge.hallyn@...ntu.com>,
	Aditya Kali <adityakali@...gle.com>,
	Chris Wilson <chris@...is-wilson.co.uk>,
	linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
	Christian Brauner <cbrauner@...e.de>, dev@...ncontainers.org
Subject: Re: [PATCH v1 2/3] cgroup: allow for unprivileged subtree management

Hello, Aleksa.

On Tue, Jul 19, 2016 at 02:18:15AM +1000, Aleksa Sarai wrote:
> +static int cgroup_permission(struct inode *inode, struct kernfs_node *kn,
> +			     int mask)
> +{
> +	int ret;
> +	struct cgroup *cgroup;
> +	struct cgroup_namespace *cgroupns;
> +
> +	/*
> +	 * First, compute the generic_permission return value. In most cases
> +	 * this will succeed and we can also avoid duplicating this code.
> +	 */
> +
> +	cgroup = kn->priv;
> +	cgroup_get(cgroup);

This pattern which is repated for cgroupns doesn't make sense.  The
code is already assuming that the cgroup is safe to deref.  Getting
its reference doesn't do anything.  Getting it here would only make
sense if the pointer is passed to an asynchronous context.

Thanks.

-- 
tejun