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[209.85.208.51]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-a93c2776d92sm165232166b.29.2024.09.27.12.28.57 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 27 Sep 2024 12:28:57 -0700 (PDT) Received: by mail-ed1-f51.google.com with SMTP id 4fb4d7f45d1cf-5c4146c7d5dso2719578a12.3 for ; Fri, 27 Sep 2024 12:28:57 -0700 (PDT) X-Forwarded-Encrypted: i=1; AJvYcCWEx8eIi2UxP7POb6NLGmk5/veL/a8ReyDw/qiqmoIknxdpVxAbRgkF6dfEP6+mZpACH164lhJbew==@kvack.org X-Received: by 2002:a17:907:36c5:b0:a86:7514:e649 with SMTP id a640c23a62f3a-a93c4a69d42mr423065966b.52.1727465337418; Fri, 27 Sep 2024 12:28:57 -0700 (PDT) MIME-Version: 1.0 References: <4167e6f5-4ff9-4aaa-915e-c1e692ac785a@efficios.com> <48992c9f-6c61-4716-977c-66e946adb399@efficios.com> <2b2aea37-06fe-40cb-8458-9408406ebda6@efficios.com> <55633835-242c-4d7f-875b-24b16f17939c@huaweicloud.com> <54487a36-f74c-46c3-aed7-fc86eaaa9ca2@huaweicloud.com> <0b262fe5-2fc5-478d-bf66-f208723238d5@efficios.com> <7e1c8a5e-c110-414c-8fb2-022eacc2bd4a@efficios.com> <34ec590c-b109-44a0-8bfe-8aafc6e7ad64@efficios.com> <1b04e35c-8994-48d9-907a-966bb4dfabaf@huaweicloud.com> In-Reply-To: <1b04e35c-8994-48d9-907a-966bb4dfabaf@huaweicloud.com> From: Linus Torvalds Date: Fri, 27 Sep 2024 12:28:40 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [RFC PATCH 1/4] hazptr: Add initial implementation of hazard pointers To: Jonas Oberhauser Cc: Mathieu Desnoyers , Boqun Feng , linux-kernel@vger.kernel.org, rcu@vger.kernel.org, linux-mm@kvack.org, lkmm@lists.linux.dev, "Paul E. McKenney" , Frederic Weisbecker , Neeraj Upadhyay , Joel Fernandes , Josh Triplett , "Uladzislau Rezki (Sony)" , rostedt , Lai Jiangshan , Zqiang , Peter Zijlstra , Ingo Molnar , Will Deacon , Waiman Long , Mark Rutland , Thomas Gleixner , Kent Overstreet , Vlastimil Babka , maged.michael@gmail.com, Neeraj Upadhyay , Greg Kroah-Hartman Content-Type: text/plain; charset="UTF-8" X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: E98FE80003 X-Stat-Signature: ns9yeg51t7bsojqj1qq1at93p96p81cq X-HE-Tag: 1727465340-523068 X-HE-Meta: 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 1xt02gwE 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 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: List-Subscribe: List-Unsubscribe: On Fri, 27 Sept 2024 at 12:12, Jonas Oberhauser wrote: > > I think it depends on which one you hide. No. Dammit, people, read the code I posted. > But for > > z = a; > hide(z); > if (z==b) { *b; } No. I *intentionally* made it an inline function, and only hid the arguments to the equality comparison. So the "hide(z)" hides the argument to the inline function - NOT THE ORIGINAL. > then it would still know that b == z, and could replace *b with *z > (which really is *a). No. The hiding is literally *ONLY* for the comparison. It's inside the helper function. It doesn't affect the originals at all. Which means that the compiler CANNOT KNOW anything about the original pointers when it compares for equality (or inequality). Basically, the comparison is now a black box to the compiler, and the compiler cannot use the result of the comparison to make ANY judgment on whether the two original pointers were related or not. Linus