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Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Jann Horn , Pedro Falcato , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20250903232437.1454293-1-kaleshsingh@google.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZoEEwEIAEQCGwMCF4ACGQEFCwkIBwICIgIG FQoJCAsCBBYCAwECHgcWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaJzangUJJlgIpAAKCRBN 3hD3AP+DWhAxD/9wcL0A+2rtaAmutaKTfxhTP0b4AAp1r/eLxjrbfbCCmh4pqzBhmSX/4z11 opn2KqcOsueRF1t2ENLOWzQu3Roiny2HOU7DajqB4dm1BVMaXQya5ae2ghzlJN9SIoopTWlR 0Af3hPj5E2PYvQhlcqeoehKlBo9rROJv/rjmr2x0yOM8qeTroH/ZzNlCtJ56AsE6Tvl+r7cW 3x7/Jq5WvWeudKrhFh7/yQ7eRvHCjd9bBrZTlgAfiHmX9AnCCPRPpNGNedV9Yty2Jnxhfmbv Pw37LA/jef8zlCDyUh2KCU1xVEOWqg15o1RtTyGV1nXV2O/mfuQJud5vIgzBvHhypc3p6VZJ lEf8YmT+Ol5P7SfCs5/uGdWUYQEMqOlg6w9R4Pe8d+mk8KGvfE9/zTwGg0nRgKqlQXrWRERv cuEwQbridlPAoQHrFWtwpgYMXx2TaZ3sihcIPo9uU5eBs0rf4mOERY75SK+Ekayv2ucTfjxr Kf014py2aoRJHuvy85ee/zIyLmve5hngZTTe3Wg3TInT9UTFzTPhItam6dZ1xqdTGHZYGU0O otRHcwLGt470grdiob6PfVTXoHlBvkWRadMhSuG4RORCDpq89vu5QralFNIf3EysNohoFy2A LYg2/D53xbU/aa4DDzBb5b1Rkg/udO1gZocVQWrDh6I2K3+cCs7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <20250903232437.1454293-1-kaleshsingh@google.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: pXC_11AYEUKDbxOlRPmB9ifts783DENIdrKSPRUjHt8_1756980886 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: F31EAC0004 X-Stat-Signature: ttwy7q31gx3wg5bj4k8abzw668djhfxw X-Rspam-User: X-HE-Tag: 1756980888-146702 X-HE-Meta: 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 8RWKWzZI 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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 04.09.25 01:24, Kalesh Singh wrote: > The check against the max map count (sysctl_max_map_count) was > open-coded in several places. This led to inconsistent enforcement > and subtle bugs where the limit could be exceeded. > > For example, some paths would check map_count > sysctl_max_map_count > before allocating a new VMA and incrementing the count, allowing the > process to reach sysctl_max_map_count + 1: > > int do_brk_flags(...) > { > if (mm->map_count > sysctl_max_map_count) > return -ENOMEM; > > /* We can get here with mm->map_count == sysctl_max_map_count */ > > vma = vm_area_alloc(mm); > ... > mm->map_count++ /* We've now exceeded the threshold. */ > } > > To fix this and unify the logic, introduce a new function, > exceeds_max_map_count(), to consolidate the check. All open-coded > checks are replaced with calls to this new function, ensuring the > limit is applied uniformly and correctly. > > To improve encapsulation, sysctl_max_map_count is now static to > mm/mmap.c. The new helper also adds a rate-limited warning to make > debugging applications that exhaust their VMA limit easier. > > Cc: Andrew Morton > Cc: Minchan Kim > Cc: Lorenzo Stoakes > Signed-off-by: Kalesh Singh > --- > include/linux/mm.h | 11 ++++++++++- > mm/mmap.c | 15 ++++++++++++++- > mm/mremap.c | 7 ++++--- > mm/nommu.c | 2 +- > mm/util.c | 1 - > mm/vma.c | 6 +++--- > 6 files changed, 32 insertions(+), 10 deletions(-) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index 1ae97a0b8ec7..d4e64e6a9814 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -192,7 +192,16 @@ static inline void __mm_zero_struct_page(struct page *page) > #define MAPCOUNT_ELF_CORE_MARGIN (5) > #define DEFAULT_MAX_MAP_COUNT (USHRT_MAX - MAPCOUNT_ELF_CORE_MARGIN) > > -extern int sysctl_max_map_count; > +/** > + * exceeds_max_map_count - check if a VMA operation would exceed max_map_count > + * @mm: The memory descriptor for the process. > + * @new_vmas: The number of new VMAs the operation will create. It's not always a "will" right? At least I remember that this was the worst case scenario in some ("may split"). "The number of new VMAs the operation may create in the worst case. -- Cheers David / dhildenb