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

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Message-ID: <u7h5zfjxz7yo6e2ukrlnznj4ug66pgu2cel4jqejjji4lzphv7@2b4ntlfl7q2g>
Date: Thu, 14 Nov 2024 14:48:16 +0100
From: Michal Koutný <mkoutny@...e.com>
To: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
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 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 for fixing this locking situation in general,
Michal

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