linux-kernel - Re: [PATCH v2 2/2] cgroup, kernfs: Move cgroup to the RCU interface for name lookups

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Message-ID: <ZzOlhANLYxFaIix2@slm.duckdns.org>
Date: Tue, 12 Nov 2024 08:59:16 -1000
From: Tejun Heo <tj@...nel.org>
To: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc: cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
	Michal Koutný <mkoutny@...e.com>,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Boqun Feng <boqun.feng@...il.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Hillf Danton <hdanton@...a.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Marco Elver <elver@...gle.com>, Zefan Li <lizefan.x@...edance.com>,
	tglx@...utronix.de,
	syzbot+6ea37e2e6ffccf41a7e6@...kaller.appspotmail.com
Subject: Re: [PATCH v2 2/2] cgroup, kernfs: Move cgroup to the RCU interface
 for name lookups

Hello,

On Tue, Nov 12, 2024 at 04:52:39PM +0100, Sebastian Andrzej Siewior wrote:
...
>  /**
> - * pr_cont_kernfs_name - pr_cont name of a kernfs_node
> + * pr_cont_kernfs_name_rcu - pr_cont name of a kernfs_node
>   * @kn: kernfs_node of interest
>   *
> - * This function can be called from any context.
> + * This function can be called from any context. The root node must be with
> + * KERNFS_ROOT_SAME_PARENT.
>   */
> -void pr_cont_kernfs_name(struct kernfs_node *kn)
> +void pr_cont_kernfs_name_rcu(struct kernfs_node *kn)

Having to split the interface all the way up isn't great. While there are
also downsides, I wonder whether a better approach here is just making the
backend function (kernfs_path_from_node()) automatically use RCU locking if
the flag is set rather than propagating the difference by splitting the
interface. The distinction doesn't mean anything to most users after all.

Thanks.

-- 
tejun