linux-kernel - Re: [PATCH 14/17] prmem: llist, hlist, both plain and rcu

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Date:   Fri, 26 Oct 2018 11:38:04 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Igor Stoppa <igor.stoppa@...il.com>
Cc:     Mimi Zohar <zohar@...ux.vnet.ibm.com>,
        Kees Cook <keescook@...omium.org>,
        Matthew Wilcox <willy@...radead.org>,
        Dave Chinner <david@...morbit.com>,
        James Morris <jmorris@...ei.org>,
        Michal Hocko <mhocko@...nel.org>,
        kernel-hardening@...ts.openwall.com,
        linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org, igor.stoppa@...wei.com,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Jonathan Corbet <corbet@....net>,
        Laura Abbott <labbott@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        "David S. Miller" <davem@...emloft.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Philippe Ombredanne <pombredanne@...b.com>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Josh Triplett <josh@...htriplett.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 14/17] prmem: llist, hlist, both plain and rcu

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@...wei.com>
> CC: Thomas Gleixner <tglx@...utronix.de>
> CC: Kate Stewart <kstewart@...uxfoundation.org>
> CC: "David S. Miller" <davem@...emloft.net>
> CC: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> CC: Philippe Ombredanne <pombredanne@...b.com>
> CC: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
> CC: Josh Triplett <josh@...htriplett.org>
> CC: Steven Rostedt <rostedt@...dmis.org>
> CC: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
> CC: Lai Jiangshan <jiangshanlai@...il.com>
> CC: linux-kernel@...r.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?