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b=fjWm5zFmBi+HFOZUFT8lO339NLFh+VE9s/5khZImm3kWAU1wgPW9lvoDfTJuXgqOT uK6JswN6Ym0CLElSIPd8I6Bzjxn/nQ5B0qTUT44fW7nT4U+bXBJIdnEkB0qQiDAPrW ieP/quKnqWB88KmYr7JCaR/FEO/tiwIHPnQVKgPk= Date: Fri, 13 Feb 2026 08:58:42 -0800 From: Andrew Morton To: Arnd Bergmann Cc: Johannes Weiner , Axel Rasmussen , Yuanchu Xie , Arnd Bergmann , Wei Xu , David Hildenbrand , Michal Hocko , Qi Zheng , Shakeel Butt , Lorenzo Stoakes , Baolin Wang , Kairui Song , Davidlohr Bueso , Koichiro Den , Jiayuan Chen , Bertrand Wlodarczyk , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/vmscan: avoid false-positive -Wuninitialized warning Message-Id: <20260213085842.0654f70a73ec05d88908ec25@linux-foundation.org> In-Reply-To: <20260213123902.3466040-1-arnd@kernel.org> References: <20260213123902.3466040-1-arnd@kernel.org> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 51FC980005 X-Stat-Signature: 3nr5tpyer444y4yzad17oecnw77sbs5g X-Rspam-User: X-HE-Tag: 1771001924-671983 X-HE-Meta: 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 EKQr87MM GamvQliW93hmjJ/6pmaljjoJwCe3J/l3T6fVoLX8ko7dxL9zlx5M5Lb9tbrCkrPNhEzoVieYDUU8DZdQH7bFMZCnzq0MaWXes0vRgkqlloxrvmum/FCDzaNqq7/eWa/4Ney35r6dvSzrS9Ygp20hozlZppcPQWWR1i6cd5AL2gm5rWGKQRqqefbL/VmZi3CH98vhaUY1VlZ6TWiMfk65eiGTOM21qL80u3Avw9Q9bnoqv0Nh9Ur1cvrKqgdqZEJil8N5cCRZDLz4QqD7ijAZ+Qs7VfQ== 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, 13 Feb 2026 13:38:56 +0100 Arnd Bergmann wrote: > From: Arnd Bergmann > > When the -fsanitize=bounds sanitizer is enabled, Is this an option in current kernels? > gcc-16 sometimes runs > into a corner case in the read_ctrl_pos() pos function, where it sees > possible undefined behavior from the 'tier' index overflowing, presumably > in the case that this was called with a negative tier: > > In function 'get_tier_idx', > inlined from 'isolate_folios' at mm/vmscan.c:4671:14: > mm/vmscan.c: In function 'isolate_folios': > mm/vmscan.c:4645:29: error: 'pv.refaulted' is used uninitialized [-Werror=uninitialized] > > Part of the problem seems to be that read_ctrl_pos() has unusual calling > conventions since commit 37a260870f2c ("mm/mglru: rework type selection") > where passing MAX_NR_TIERS makes it accumulate all tiers but passing a > smaller positive number makes it read a single tier instead. > > Avoid this case by splitting read_ctrl_pos() into two separate helpers > that each only do one of the two cases. This avoids the warning as far > as I can tell, and seems a bit easier to understand to me. > > Signed-off-by: Arnd Bergmann > --- > This is currently the only such warning I get from gcc-16.0.1, and > none from any other version. > > I'm not overly happy about having to work around it with a random > code chance, but hopefully the version I ended up with makes > sense regardless. Seems a large change just to squish a compiler warning. People might prefer a simple - struct ctrl_pos sp, pv; + struct ctrl_pos sp, pv = {}; ?