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b=J7dVm3oHxaqbESIAhtHy/bRJtU3jMAYnjBfyqsVKCpUV/oYma6wQBIy43T1apTF5d +oYJcB1kApd10QnaJnvJ70khNnecrLLls2qcuD1K85jNf6ub9QlRv6dxjx4crlmv5V w0oyR8ZjbbnX9dQ/51UFQKfcqL8FQHZEYc3h6LHM= Date: Wed, 25 Mar 2026 16:57:16 -0700 From: Andrew Morton To: Qi Zheng Cc: hannes@cmpxchg.org, hughd@google.com, mhocko@suse.com, roman.gushchin@linux.dev, shakeel.butt@linux.dev, muchun.song@linux.dev, david@kernel.org, ljs@kernel.org, ziy@nvidia.com, harry.yoo@oracle.com, yosry.ahmed@linux.dev, imran.f.khan@oracle.com, kamalesh.babulal@oracle.com, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, chenridong@huaweicloud.com, mkoutny@suse.com, hamzamahfooz@linux.microsoft.com, apais@linux.microsoft.com, lance.yang@linux.dev, bhe@redhat.com, usamaarif642@gmail.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Qi Zheng Subject: Re: [PATCH v2 0/4] fix unexpected type conversions and potential overflows Message-Id: <20260325165716.5d63522ba825f25a63e74e3e@linux-foundation.org> In-Reply-To: References: X-Mailer: Sylpheed 3.7.0 (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-Rspam-User: X-Rspamd-Queue-Id: A61514000A X-Stat-Signature: r1niie5tpaw18khfzj6uwk3mqag4i8af X-Rspamd-Server: rspam06 X-HE-Tag: 1774483038-669400 X-HE-Meta: U2FsdGVkX19RexlfuD3304Zy3kF9IwZWFKe1ajntXii9IGMVmoRyCkwTc1aDkxERmNHrIODTCXQjSQZ5J+4WpFehdWLqK1jJpOI/5NyLXhuI3RUw5qs/qvG4BQBS3f6f3LU23NDQKNpwD1uIDhRKAU/gt7oWM6CZUOjOWtEH0zKomF5unQOooiEBWiCEH8tOjeR6vxAXANBGWTkNtwJ3A4rw4TsFaVm0o8eAqGzqFbLqc7LTFmU9Yqe2wVeMIQjh6xlTDAGGAvUrNLZm78NNna5rTGYNp+9ZANq/nX99jny72fQnPzEUi1+DhtJJ4e5SMqsDLLJpTyi9GAfg3qokkccWmTf8wW8Vf/NACoIYlzcip63O+GymVe4If3Yfpp7Bc6Vm5B6NC+zbwiaAqs53WgwcTJnMMTm9ky+TchRU5AD6OhPYXYMVPxlDipz6r4ZGftnwCmE6GCaFwaQ34PUnNpghrpSkmsBKo6u+piaJriBo6wjARChX2woPY+ZpqapCcv8bLLHkqLYsV6yzefFPPVABO1ScqTINrv9YTLBg8jgFA9NrjgiV+mSWHEyFynURN6+2ScDvTnt+Y80VXIaqTEMxN7D05771rbh+vaEkcShO+O8Xz8XF/HykYoUjsPN8fLvPWPa7UybIn4EO/eM5PSRpmcEdnK0weTM/9T8nuqccYqZvluOc4J9RfJzb0SM38W18oYQUpVqXFEfuR8uhobxgFkCyz9VowcDNl+typ/e6m8u55AWflEHUXLcsrgUSR0L6DEVZKui1Og8NT+swxngRgPOPvkOf8o+/2dUgVQOD5gvM2xuwbpX0pxmye+IAe62VbL7UiUIET+Al7vP/MGkynxaD5ijPI4VOInisFrsckCr4MSo8qmVnzg48oRb4Wqi3CgJLmXMPf53Q7VVEb4vD1EXlntJdU6pO5LxkviuTXR0yniUzp4cleo1s4bjgwxj+ZvHjiL0R3BN9Py1 GfkDqhdg sh+R4Hc/8In9Xcr8IxHOsABRfKXVf4rADyAEUYDexaxtUyLNe2HnCqv2INiPpdIbs0IzEwtVh0cBdWylXZjAJpexc1oAGLrZm2oRg72+g0xkYohJH/fcgG2zOeW5s10m5SWmHNsMd/J9uHaFHrR+YAmfWNHJmC2MkS9GIx/hUngaHmSrqCzpJYxJog1WCWAE0v7TkiWuiR4+2Absm4hOG4HE+mrJrdx9S+qDcOvZPtZtDqgfUgG8lbSgR86Sw3WSNQ4h5Z2SwtDQdy7r6MGRDCCrIOuhkMABlKXC0f8sVJaSztCObEmyOk7A0ZmVUPb/CuXPHxRiMaY1huHR5EadPZ48JnYnKkcezhSOW3RNkeWuD2PI= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, 25 Mar 2026 22:13:21 +0800 Qi Zheng wrote: > As Harry Yoo pointed out [1], in scenarios where massive state updates occur > (e.g., during the reparenting of LRU folios), the values passed to memcg stat > update functions can accumulate and exceed the upper limit of a 32-bit integer. > > If the parameter types are not large enough (like 'int') or are handled > incorrectly, it can lead to severe truncation, potential overflow issues, > and unexpected type conversion bugs. > > This series aims to address these issues by correcting the parameter types > in the relevant functions, and fixing an implicit conversion bug in > memcg_state_val_in_pages(). Thanks. I'll add this to mm.git's mm-new branch. AI review (https://sashiko.dev/#/patchset/cover.1774447069.git.zhengqi.arch%40bytedance.com) still points at the problem in [2/4], now describing it as a bisection hole. In https://lkml.kernel.org/r/5fed0611-434c-4fd4-956c-39f23e0459a1@linux.dev you said you were going to address this by using abs(), and I see that being done in [4/4] so yup, runtime bisection hole. I'm inclined to mark this "don't care". But if we decide to backport [2/4] ("to prevent potential overflow issues") then we might have a problem. Also, if some downstream person decides to backport [2/4] into their kernel without [4/4] then they'll have a bad day. So perhaps this issue should be addressed within [2/4]?