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Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1r4opV-0032da-18; Sun, 19 Nov 2023 20:55:45 +0000 Date: Sun, 19 Nov 2023 20:55:44 +0000 From: Matthew Wilcox To: Kairui Song Cc: linux-mm@kvack.org, Andrew Morton , "Huang, Ying" , David Hildenbrand , Hugh Dickins , Johannes Weiner , Michal Hocko , linux-kernel@vger.kernel.org Subject: Re: [PATCH 01/24] mm/swap: fix a potential undefined behavior issue Message-ID: References: <20231119194740.94101-1-ryncsn@gmail.com> <20231119194740.94101-2-ryncsn@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20231119194740.94101-2-ryncsn@gmail.com> X-Stat-Signature: bkba8d7znbc5pb46pntoderw4boijky1 X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: E766C20009 X-Rspam-User: X-HE-Tag: 1700427354-264292 X-HE-Meta: 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 OQno0bwq PiCSDgHW+QVK9EYN+zDg6Fp9QGa8vIhc6wE3EDqWUjZWBmfBxQZn5UihyAtbr/NdvNGbBruV/MmPfQmqQB4n+3bgHmVd04ZeBdhkr+NzxkTAo8k7uCoWMxToVRV+7SmGtQLwuTvHZdr8R+So4cOTind2800XYrszTuSqWEdMeZgO1Hr+l6Oj/1TbFVB9+yn71KOBM 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 Mon, Nov 20, 2023 at 03:47:17AM +0800, Kairui Song wrote: > From: Kairui Song > > When folio is NULL, taking the address of its struct member is an > undefined behavior, the UB is caused by applying -> operator > to a pointer not pointing to any object. Although in practice this > won't lead to a real issue, still better to fix it, also makes the > code less error-prone, when folio is NULL, page is also NULL, > instead of a meanless offset value. Um, &folio->page is NULL if folio is NULL. The offset of 'page' within 'folio' is 0. By definition; and this will never change.