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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Michal =?utf-8?Q?Koutn=C3=BD?= <mkoutny@suse.com>
Cc: cgroups@vger.kernel.org, linux-kernel@vger.kernel.org,
	"Paul E. McKenney" <paulmck@kernel.org>,
	Boqun Feng <boqun.feng@gmail.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Hillf Danton <hdanton@sina.com>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Marco Elver <elver@google.com>, Tejun Heo <tj@kernel.org>,
	Zefan Li <lizefan.x@bytedance.com>, tglx@linutronix.de
Subject: Re: [PATCH v2 1/2] kernfs: Make it possible to use RCU for
 kernfs_node::name lookup.
Message-ID: <20241115173256.13IVHFNn@linutronix.de>
References: <20241112155713.269214-1-bigeasy@linutronix.de>
 <20241112155713.269214-2-bigeasy@linutronix.de>
 <u7h5zfjxz7yo6e2ukrlnznj4ug66pgu2cel4jqejjji4lzphv7@2b4ntlfl7q2g>
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In-Reply-To: <u7h5zfjxz7yo6e2ukrlnznj4ug66pgu2cel4jqejjji4lzphv7@2b4ntlfl7q2g>

On 2024-11-14 14:48:16 [+0100], Michal Koutn=C3=BD wrote:
> On Tue, Nov 12, 2024 at 04:52:38PM GMT, Sebastian Andrzej Siewior <bigeas=
y@linutronix.de> wrote:
> > --- a/include/linux/kernfs.h
> > +++ b/include/linux/kernfs.h
> > @@ -147,6 +147,11 @@ enum kernfs_root_flag {
> >  	 * Support user xattrs to be written to nodes rooted at this root.
> >  	 */
> >  	KERNFS_ROOT_SUPPORT_USER_XATTR		=3D 0x0008,
> > +
> > +	/*
> > +	 * Renames must not change the parent node.
> > +	 */
> > +	KERNFS_ROOT_SAME_PARENT			=3D 0x0010,
>=20
> FTR, cgroup v2 doesn't even define renames and the full rename
> (different parent) is only used by resctrl filesystem AFAICS.
> I'm only mentioning it in the case you wanted to replace the flag with
> two different rename methods in kernfs_syscall_ops.

Thanks. I think I have enough clues for a v3 now. I wanted to do
something today but didn't manage it yet.

> Thanks for fixing this locking situation in general,
> Michal

Sebastian