linux-kernel - Re: [PATCH v2 1/2] kernfs: Make it possible to use RCU for kernfs

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Message-ID: <20241115173256.13IVHFNn@linutronix.de>
Date: Fri, 15 Nov 2024 18:32:56 +0100
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: Michal Koutný <mkoutny@...e.com>
Cc: cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
	"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>, Tejun Heo <tj@...nel.org>,
	Zefan Li <lizefan.x@...edance.com>, tglx@...utronix.de
Subject: Re: [PATCH v2 1/2] kernfs: Make it possible to use RCU for
 kernfs_node::name lookup.

On 2024-11-14 14:48:16 [+0100], Michal Koutný wrote:
> On Tue, Nov 12, 2024 at 04:52:38PM GMT, Sebastian Andrzej Siewior <bigeasy@...utronix.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		= 0x0008,
> > +
> > +	/*
> > +	 * Renames must not change the parent node.
> > +	 */
> > +	KERNFS_ROOT_SAME_PARENT			= 0x0010,
> 
> 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