linux-kernel - Re: [PATCH] provide arch_test_bit_acquire for architectures that define test

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Date:   Fri, 26 Aug 2022 16:10:01 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Mikulas Patocka <mpatocka@...hat.com>
Cc:     Brian Cain <bcain@...cinc.com>, linux-hexagon@...r.kernel.org,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Alan Stern <stern@...land.harvard.edu>,
        Andrea Parri <parri.andrea@...il.com>,
        Will Deacon <will@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Boqun Feng <boqun.feng@...il.com>,
        Nicholas Piggin <npiggin@...il.com>,
        David Howells <dhowells@...hat.com>,
        Jade Alglave <j.alglave@....ac.uk>,
        Luc Maranget <luc.maranget@...ia.fr>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Akira Yokosawa <akiyks@...il.com>,
        Daniel Lustig <dlustig@...dia.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux-Arch <linux-arch@...r.kernel.org>
Subject: Re: [PATCH] provide arch_test_bit_acquire for architectures that
 define test_bit

On Fri, Aug 26, 2022 at 1:43 PM Mikulas Patocka <mpatocka@...hat.com> wrote:
>
> I'm wondering why do the architectures redefine test_bit, if their
> definition is equivalent to the generic one? We could just delete
> arch_test_bit and use "#define arch_test_bit generic_test_bit" as well.

I think generic_test_bit() came after many of them, and when it
didn't, people copied earlier architectures where they had already
done their own.

> Another untested patch ... tomorrow, I'll try to compile it, at least for
> architectures where Debian provides cross-compiling gcc.

Looks good to me, except I'd just do

#define arch_test_bit_acquire arch_test_bit

on hexagon rather than duplicate that function.

>From my reading, Hexagon doesn't have any fancy memory ordering, it's
just the usual UP with barriers basically for instruction cache
coherence etc.

                 Linus