linux-kernel - Re: [PATCH v4 6/6] kernfs: Use RCU to access kernfs

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Message-ID: <20250127161736.6aq3z3KP@linutronix.de>
Date: Mon, 27 Jan 2025 17:17:36 +0100
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: Tejun Heo <tj@...nel.org>
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 v4 6/6] kernfs: Use RCU to access kernfs_node::name.

On 2025-01-24 13:41:17 [-1000], Tejun Heo wrote:
> Hello,
> 
> On Fri, Jan 24, 2025 at 06:46:14PM +0100, Sebastian Andrzej Siewior wrote:
> > Using RCU lifetime rules to access kernfs_node::name can avoid the
> > trouble kernfs_rename_lock in kernfs_name() and kernfs_path_from_node()
> > if the fs was created with KERNFS_ROOT_INVARIANT_PARENT.
> 
> Maybe explain why we want to do this?
> 
> > +static inline const char *kernfs_rcu_get_name(const struct kernfs_node *kn)
> > +{
> > +	return rcu_dereference_check(kn->name, kernfs_root_is_locked(kn));
> > +}
> 
> Can you drop "get" from the accessors? Other accessors don't have it and it
> gets confusing with reference counting operations.

Sure.

> Thanks.

Sebastian