linux-kernel - Re: [GIT PULL] RCU regression fix for v6.4

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Message-ID: <CAHk-=wiPA8d0z2K1huqP0jCKxfmjBG_VYnJtoADeQWsvWLv9UQ@mail.gmail.com>
Date:   Fri, 16 Jun 2023 11:50:31 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     paulmck@...nel.org
Cc:     linux-kernel@...r.kernel.org, kernel-team@...a.com,
        rcu@...r.kernel.org, jonathanh@...dia.com, wenst@...omium.org,
        angelogioacchino.delregno@...labora.com,
        rafael.j.wysocki@...el.com, mirq-linux@...e.qmqm.pl,
        dmitry.osipenko@...labora.com, sachinp@...ux.ibm.com,
        qiang.zhang1211@...il.com
Subject: Re: [GIT PULL] RCU regression fix for v6.4

On Fri, 16 Jun 2023 at 09:34, Paul E. McKenney <paulmck@...nel.org> wrote:
>
> Yes, it would be nice to abstract this somehow in order to hide it in
> SRCU, but I still don't see a good way of doing this.

Ehh - like we actually do spinlocks in general, perhaps?

Spinlocks always exist. On UP - with no spinlock debugging - it turns
into a zero-sized data structure, and the spin lock/unlock operations
are no-ops.

Why don't you just do the exact same thing with the "struct
srcu_usage". For Tiny SRCU, just make it an empty struct, with an
empty initializer.

IOW, don't "abstract it out". Abstract it IN. Make tiny-rcu still have
it, just as a no-op.

Anyway, I've pulled your fix, but maybe the above would have been the
cleaner solution?

          Linus