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[209.85.167.54]) by smtp.gmail.com with ESMTPSA id v3sm1452432lfo.62.2020.04.07.13.07.05 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 07 Apr 2020 13:07:05 -0700 (PDT) Received: by mail-lf1-f54.google.com with SMTP id 131so3347425lfh.11 for ; Tue, 07 Apr 2020 13:07:05 -0700 (PDT) X-Received: by 2002:ac2:4466:: with SMTP id y6mr2462517lfl.125.1586290024968; Tue, 07 Apr 2020 13:07:04 -0700 (PDT) MIME-Version: 1.0 References: <20200406200254.a69ebd9e08c4074e41ddebaf@linux-foundation.org> <20200407031042.8o-fYMox-%akpm@linux-foundation.org> <158627540139.8918.10102358634447361335@build.alporthouse.com> <158628265081.8918.1825514020221532657@build.alporthouse.com> In-Reply-To: From: Linus Torvalds Date: Tue, 7 Apr 2020 13:06:48 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [patch 125/166] lib/list: prevent compiler reloads inside 'safe' list iteration To: Chris Wilson Cc: Andrew Morton , David Laight , Marco Elver , Linux-MM , Mark Rutland , mm-commits@vger.kernel.org, "Paul E. McKenney" , Randy Dunlap , stable Content-Type: text/plain; charset="UTF-8" X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Apr 7, 2020 at 1:04 PM Linus Torvalds wrote: > > You may be relying on some very subtle consistency guarantee that is > true on x86. For example, x86 does guarantee "causality". > > Not everybody else does that. It's worth noting that maybe for the i915 driver it makes sense to just assume x86 memory ordering. But even if that's the case, then it doesn't make sense to change list_prev_entry_safe() anywhere else. Linus