linux-kernel - Re: [GIT PULL] RCU changes for v5.10

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Message-ID: <CAHk-=wiWowWNsrOh+Ye+b_x=7_4MQmvXq0cdmLwqr2=YYj-jgA@mail.gmail.com>
Date:   Mon, 12 Oct 2020 13:25:09 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [GIT PULL] RCU changes for v5.10

On Mon, Oct 12, 2020 at 7:14 AM Ingo Molnar <mingo@...nel.org> wrote:
>
> Please pull the latest core/rcu git tree from:
>
> RCU changes for v5.10:
>
>  - Debugging for smp_call_function()
>  - RT raw/non-raw lock ordering fixes
>  - Strict grace periods for KASAN
>  - New smp_call_function() torture test
>  - Torture-test updates
>  - Documentation updates
>  - Miscellaneous fixes

I am *very* unhappy with this pull request.

It doesn't even mention the big removal of CONFIR_PREEMPT, that I felt
was still under discussion.

I don't absolutely hate that code, and I'm willing to be convinced
about how little it matter for people who don't want to have the
counting overhead, but I refuse to pull it as some secret hidden thing
that isn't even mentioned in the pull request.

Honestly, I did not get any strong arguments for why making the
preempt count unconditional was such an important thing.

Yes, Thomas pointed me at a couple of uses that were garbage, but even
the people involved in those seemed to agree they were legacy garbage.

So why was this preempt-count thing then pushed through like this?

                 Linus