linux-kernel - Re: [RFC PATCH] LKMM: Add ctrl_dep() macro for control dependency

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Message-ID: <CAHk-=wgexLqNnngLPts=wXrRcoP_XHO03iPJbsAg8HYuJbbAvw@mail.gmail.com>
Date:   Fri, 1 Oct 2021 09:35:47 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Florian Weimer <fweimer@...hat.com>
Cc:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Segher Boessenkool <segher@...nel.crashing.org>,
        Will Deacon <will@...nel.org>, paulmck <paulmck@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Alan Stern <stern@...land.harvard.edu>,
        Andrea Parri <parri.andrea@...il.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Nicholas Piggin <npiggin@...il.com>,
        David Howells <dhowells@...hat.com>,
        j alglave <j.alglave@....ac.uk>,
        luc maranget <luc.maranget@...ia.fr>,
        akiyks <akiyks@...il.com>,
        linux-toolchains <linux-toolchains@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>
Subject: Re: [RFC PATCH] LKMM: Add ctrl_dep() macro for control dependency

On Fri, Oct 1, 2021 at 9:26 AM Florian Weimer <fweimer@...hat.com> wrote:
>
> Will any conditional branch do, or is it necessary that it depends in
> some way on the data read?

The condition needs to be dependent on the read.

(Easy way to see it: if the read isn't related to the conditional or
write data/address, the read could just be delayed to after the
condition and the store had been done).

               Linus