linux-kernel - Re: [RFC PATCH 01/20] asm-generic/mmiowb: Add generic implementation of mmiowb() tracking

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Message-ID: <CAHk-=wjx89RpPw6EV4fwSDAPbQcs=-2a4oM9N94saa9hemNbmw@mail.gmail.com>
Date:   Tue, 26 Feb 2019 11:02:50 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Will Deacon <will.deacon@....com>,
        linux-arch <linux-arch@...r.kernel.org>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        "Paul E. McKenney" <paulmck@...ux.ibm.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Arnd Bergmann <arnd@...db.de>,
        Andrea Parri <andrea.parri@...rulasolutions.com>,
        Palmer Dabbelt <palmer@...ive.com>,
        Daniel Lustig <dlustig@...dia.com>,
        David Howells <dhowells@...hat.com>,
        Alan Stern <stern@...land.harvard.edu>,
        "Maciej W. Rozycki" <macro@...ux-mips.org>,
        Paul Burton <paul.burton@...s.com>,
        Ingo Molnar <mingo@...nel.org>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Rich Felker <dalias@...c.org>, Tony Luck <tony.luck@...el.com>
Subject: Re: [RFC PATCH 01/20] asm-generic/mmiowb: Add generic implementation
 of mmiowb() tracking

On Tue, Feb 26, 2019 at 10:33 AM Peter Zijlstra <peterz@...radead.org> wrote:
>
> Arguably we could fix that for __this_cpu_xchg(), which isn't IRQ-safe.

Yeah, I guess x86 _should_ really do __this_cpu_xchg() as just a
read-write pair.

In general, a read-write pair is probably always the right thing to
do, and the only reason we can't just do it in an
architecture-independent way is that we'd want to avoid doing the
address generation twice (for architectures where that is an issue).

                  Linus