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McKenney" Cc: Andrea Parri , linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, Alan Stern , Will Deacon , Boqun Feng , Nicholas Piggin , David Howells , Jade Alglave , Luc Maranget , Akira Yokosawa , Daniel Lustig Subject: Re: [RFC PATCH] tools/memory-model: Remove (dep ; rfi) from ppo Message-ID: <20190220092604.GD32494@hirez.programming.kicks-ass.net> References: <1550617057-4911-1-git-send-email-andrea.parri@amarulasolutions.com> <20190220020117.GD11787@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190220020117.GD11787@linux.ibm.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Feb 19, 2019 at 06:01:17PM -0800, Paul E. McKenney wrote: > On Tue, Feb 19, 2019 at 11:57:37PM +0100, Andrea Parri wrote: > > Remove this subtle (and, AFAICT, unused) ordering: we can add it back, > > if necessary, but let us not encourage people to rely on this thing. > > > > For example, the following "exists" clause can be satisfied with this > > change: > > > > C dep-rfi > > > > { } > > > > P0(int *x, int *y) > > { > > WRITE_ONCE(*x, 1); > > smp_store_release(y, 1); > > } > > > > P1(int *x, int *y, int *z) > > { > > int r0; > > int r1; > > int r2; > > > > r0 = READ_ONCE(*y); > > WRITE_ONCE(*z, r0); > > r1 = smp_load_acquire(z); > > r2 = READ_ONCE(*x); > > } > > > > exists (1:r0=1 /\ 1:r2=0) > > Any objections? If I don't hear any in a couple days, I will apply this. IIUC you cannot build hardware that allows the above, so why would we allow it?