linux-kernel - Re: [PATCH v2 0/4] task: Making tasks on the runqueue rcu protected

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Message-ID: <CAHk-=whej3MMKJBHKWp66djfEP5=kyncX7FoqJacYtmBXB6v9w@mail.gmail.com>
Date:   Sat, 14 Sep 2019 10:43:59 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Oleg Nesterov <oleg@...hat.com>,
        Russell King - ARM Linux admin <linux@...linux.org.uk>,
        Chris Metcalf <cmetcalf@...hip.com>,
        Christoph Lameter <cl@...ux.com>,
        Kirill Tkhai <tkhai@...dex.ru>, Mike Galbraith <efault@....de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        Davidlohr Bueso <dave@...olabs.net>,
        "Paul E. McKenney" <paulmck@...nel.org>
Subject: Re: [PATCH v2 0/4] task: Making tasks on the runqueue rcu protected

On Sat, Sep 14, 2019 at 5:30 AM Eric W. Biederman <ebiederm@...ssion.com> wrote:
>
> I have reworked these patches one more time to make it clear that the
> first 3 patches only fix task_struct so that it experiences a rcu grace
> period after it leaves the runqueue for the last time.

I remain a fan of these patches, and the added comment on the last one
is I think a sufficient clarification of the issue.

But it's patch 3 that makes me go "yeah, this is the right approach",
because it just removes subtle code in favor of something that is
understandable.

Yes, most of the lines removed may be comments, and so it doesn't
actually remove a lot of _code_, but I think the comments are a result
of just how subtle and fragile our current approach is, and the new
model not needing them as much is I think a real issue (rather than
just Eric being less verbose in the new comments and removing lines of
code that way).

Can anybody see anything wrong with the series? Because I'd love to
have it for 5.4,

             Linus