linux-kernel - Re: [PATCH 2/2] mountinfo: implement show

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Message-ID: <20160502163441.GV7822@mtj.duckdns.org>
Date:	Mon, 2 May 2016 12:34:41 -0400
From:	Tejun Heo <tj@...nel.org>
To:	serge.hallyn@...ntu.com
Cc:	linux-kernel@...r.kernel.org, adityakali@...gle.com,
	linux-api@...r.kernel.org, containers@...ts.linux-foundation.org,
	cgroups@...r.kernel.org, akpm@...ux-foundation.org,
	ebiederm@...ssion.com, gregkh@...uxfoundation.org,
	lizefan@...wei.com, hannes@...xchg.org
Subject: Re: [PATCH 2/2] mountinfo: implement show_path for kernfs and cgroup

Hello,

On Sun, Apr 17, 2016 at 03:04:32PM -0500, serge.hallyn@...ntu.com wrote:
> +static int cgroup_show_path(struct seq_file *sf, struct kernfs_node *kf_node,
> +			    struct kernfs_root *kf_root)
> +{
> +	int len = 0, ret = 0;
> +	char *buf = NULL;
> +	struct cgroup_namespace *ns = current->nsproxy->cgroup_ns;
> +	struct cgroup_root *kf_cgroot = cgroup_root_from_kf(kf_root);
> +	struct cgroup *ns_cgroup;
> +
> +	mutex_lock(&cgroup_mutex);
> +	spin_lock_bh(&css_set_lock);
> +	ns_cgroup = cset_cgroup_from_root(ns->root_cset, kf_cgroot);
> +	len = kernfs_path_from_node(kf_node, ns_cgroup->kn, NULL, 0);
> +	if (len > 0)
> +		buf = kmalloc(len + 1, GFP_ATOMIC);

Ugh... What's up with GFP_ATOMIC?  Just allocate maximum sized buffer
before grabbing any locks.

Thanks.

-- 
tejun