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b=tyVraxvY2BEJuhXBKZKHI/OF3kkdyJl/Besik/yWhboY3Gtj9Y8jeKsTTZO7eK7Qm XEM9TqDQTDt2C0X6uhfxm3eFgeLfGNxdOehskE8OFRF20DoEEc8dwC918SkB2fv90q KkQd66d38c+vJHjouWPX6sQQtq2IV4GB7vmBtabJbl6jmitpAdu6Gu104Azjr6Eeou /ZkpDTWlDPZ2WpgZpZ456gNPVb8IfBF7KpTr91lgpdp1ioc8DCL2e7pNA4ONHMARXN pj+QVYIn6fRD/EIy2YWAU3dpW0y0qWxZEV2VshBJdaQgTOi3wzODSO6Xb96wDq08Ds fntl/0Hqqz+FA== Received: by mail-pj1-f54.google.com with SMTP id 98e67ed59e1d1-28120aa1c24so3126143a91.0 for ; Mon, 20 Nov 2023 09:34:32 -0800 (PST) X-Gm-Message-State: AOJu0YwMNJbg/rWDP+qQHW1KU7Gr7xk7fa4W0w/FX3F+atrRgCb+SkMs S+Z+cNHRRzvdwRPYWsyCP5l6S1Yuky1ztKwZZ+F+eg== X-Google-Smtp-Source: AGHT+IGbynMZguQy1gy1l9Y2sMFDwbH47UZLvGUcle97Eq9G4RDIUluKrlugmvhWTvoAQYdOJDqFnBHVtYAVMpa4Brw= X-Received: by 2002:a17:90b:1b4f:b0:281:1c2e:9e6a with SMTP id nv15-20020a17090b1b4f00b002811c2e9e6amr5676311pjb.39.1700501671895; Mon, 20 Nov 2023 09:34:31 -0800 (PST) MIME-Version: 1.0 References: <20231119194740.94101-1-ryncsn@gmail.com> <20231119194740.94101-2-ryncsn@gmail.com> In-Reply-To: From: Chris Li Date: Mon, 20 Nov 2023 09:34:20 -0800 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH 01/24] mm/swap: fix a potential undefined behavior issue To: Kairui Song Cc: Matthew Wilcox , linux-mm , Andrew Morton , "Huang, Ying" , David Hildenbrand , Hugh Dickins , Johannes Weiner , Michal Hocko , LKML Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 9C39C40003 X-Stat-Signature: hkfqjkrd54hba3moi4cphm6np3p3m87s X-Rspam-User: X-HE-Tag: 1700501674-868130 X-HE-Meta: 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 RVa/6L7O 8eqLmtkVXQDz5zDvBTFFtFpWBeiURP2qXOFM0EP86z2goJYDz+ba99pCRH3l6qlMFDLdxjoaS8uHuiqffuVBXs2Alqrw3onTCVQg2xlNalfDpyasHuyYOXVzFtwLYiz5pLGSBNekEhhoda5YAI/sRtHxu24FBj+l5q7/ue9SI38HnntvHlRVADbp5cfZcRlnQIiimBpIwUU8fZG7ze5BB3E3dpg6E0mEUtW1TfIk7lmLq5Z3Wjz9bZ5CzVC86wSnScfKeUpcK6F6cjVE= 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: Hi Kairui, On Mon, Nov 20, 2023 at 3:15=E2=80=AFAM Kairui Song wrot= e: > > Chris > > Hi, Chris and Matthew. > > Thanks for the comments. > > Right, it's just a language syntax level thing, since "->" have a > higher priority, so in the syntax level it is doing a member access > first, then take the address. By C definition member access should > not happen if the object is invalid (NULL). Only a hypothesis problem > on paper... The dereference only shows up in the abstract syntax tree level. According to the C standard there are expansion and evaluation phases after that. At the evaluation phase the dereference will turn into pointer arithmetic. Per my understanding, the dereference never actually happens, due to the evaluation rules, not even in theory. > This is indeed not needed since in reality it's just pointer > arithmetic. I'm OK dropping this. Thanks Chris