Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <20210928211507.20335-1-mathieu.desnoyers@efficios.com>
 <87lf3f7eh6.fsf@oldenburg.str.redhat.com> <20210929174146.GF22689@gate.crashing.org>
 <2088260319.47978.1633104808220.JavaMail.zimbra@efficios.com> <871r54ww2k.fsf@oldenburg.str.redhat.com>
In-Reply-To: <871r54ww2k.fsf@oldenburg.str.redhat.com>
From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Fri, 1 Oct 2021 09:35:47 -0700
Message-ID: <CAHk-=wgexLqNnngLPts=wXrRcoP_XHO03iPJbsAg8HYuJbbAvw@mail.gmail.com>
Subject: Re: [RFC PATCH] LKMM: Add ctrl_dep() macro for control dependency
To:     Florian Weimer <fweimer@redhat.com>
Cc:     Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Segher Boessenkool <segher@kernel.crashing.org>,
        Will Deacon <will@kernel.org>, paulmck <paulmck@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Alan Stern <stern@rowland.harvard.edu>,
        Andrea Parri <parri.andrea@gmail.com>,
        Boqun Feng <boqun.feng@gmail.com>,
        Nicholas Piggin <npiggin@gmail.com>,
        David Howells <dhowells@redhat.com>,
        j alglave <j.alglave@ucl.ac.uk>,
        luc maranget <luc.maranget@inria.fr>,
        akiyks <akiyks@gmail.com>,
        linux-toolchains <linux-toolchains@vger.kernel.org>,
        linux-arch <linux-arch@vger.kernel.org>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Fri, Oct 1, 2021 at 9:26 AM Florian Weimer <fweimer@redhat.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