[PATCH 14/17] prmem: llist, hlist, both plain and rcu

[Peter Zijlstra]

On Wed, Oct 24, 2018 at 12:35:01AM +0300, Igor Stoppa wrote:
> In some cases, all the data needing protection can be allocated from a pool
> in one go, as directly writable, then initialized and protected.
> The sequence is relatively short and it's acceptable to leave the entire
> data set unprotected.
> 
> In other cases, this is not possible, because the data will trickle over
> a relatively long period of time, in a non predictable way, possibly for
> the entire duration of the operations.
> 
> For these cases, the safe approach is to have the memory already write
> protected, when allocated. However, this will require replacing any
> direct assignment with calls to functions that can perform write rare.
> 
> Since lists are one of the most commonly used data structures in kernel,
> they are a the first candidate for receiving write rare extensions.
> 
> This patch implements basic functionality for altering said lists.
> 
> Signed-off-by: Igor Stoppa <igor.stoppa at huawei.com>
> CC: Thomas Gleixner <tglx at linutronix.de>
> CC: Kate Stewart <kstewart at linuxfoundation.org>
> CC: "David S. Miller" <davem at davemloft.net>
> CC: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
> CC: Philippe Ombredanne <pombredanne at nexb.com>
> CC: "Paul E. McKenney" <paulmck at linux.vnet.ibm.com>
> CC: Josh Triplett <josh at joshtriplett.org>
> CC: Steven Rostedt <rostedt at goodmis.org>
> CC: Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
> CC: Lai Jiangshan <jiangshanlai at gmail.com>
> CC: linux-kernel at vger.kernel.org
> ---
>  MAINTAINERS            |   1 +
>  include/linux/prlist.h | 934 +++++++++++++++++++++++++++++++++++++++++

I'm not at all sure I understand the Changelog, or how it justifies
duplicating almost 1k lines of code.

Sure lists aren't the most complicated thing we have, but duplicating
that much is still very _very_ bad form. Why are we doing this?