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Fri, 25 Oct 2024 06:15:55 -0700 (PDT) Received: from andrea ([2a01:5a8:300:22d3:a281:3d89:19cb:ed96]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-5cbb62580b1sm618645a12.15.2024.10.25.06.15.54 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 25 Oct 2024 06:15:55 -0700 (PDT) Date: Fri, 25 Oct 2024 16:15:51 +0300 From: Andrea Parri To: Hernan Ponce de Leon Cc: puranjay@kernel.org, paulmck@kernel.org, bpf@vger.kernel.org, lkmm@lists.linux.dev, linux-kernel@vger.kernel.org Subject: Re: Some observations (results) on BPF acquire and release Message-ID: References: Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: > > BPF R+release+fence > > { > > 0:r2=x; 0:r4=y; > > 1:r2=y; 1:r4=x; 1:r6=l; > > } > > P0 | P1 ; > > r1 = 1 | r1 = 2 ; > > *(u32 *)(r2 + 0) = r1 | *(u32 *)(r2 + 0) = r1 ; > > r3 = 1 | r5 = atomic_fetch_add((u32 *)(r6 + 0), r5) ; > > store_release((u32 *)(r4 + 0), r3) | r3 = *(u32 *)(r4 + 0) ; > > exists ([y]=2 /\ 1:r3=0) > > > > This "exists" condition is not satisfiable according to the BPF model; > > however, if we adopt the "natural"/intended(?) PowerPC implementations > > of the synchronization primitives above (aka, with store_release() --> > > LWSYNC and atomic_fetch_add() --> SYNC ; [...] ), then we see that the > > condition in question becomes (architecturally) satisfiable on PowerPC > > (although I'm not aware of actual observations on PowerPC hardware). > > Are the resulting PPC tests available somewhere? My data go back to the LKMM paper, cf. e.g. the R+pooncerelease+fencembonceonce entry at https://diy.inria.fr/linux/hard.html#unseen . Andrea