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Mon, 09 Nov 2026 01:05:34 -0800 (PST) Received: from [192.168.1.22] ([83.231.69.9]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-49596ea51cbsm9541323f8f.27.2026.11.09.01.05.31 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 09 Nov 2026 01:05:33 -0800 (PST) Message-ID: <8ff83fbf-2ecb-4f9b-ac8f-ee88fece67cb@gmail.com> Date: Mon, 9 Nov 2026 10:05:30 +0100 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 5/5] mm/gup: limit pagecache folio refcount when grabbing references To: "David Hildenbrand (Arm)" , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , "Matthew Wilcox (Oracle)" , Jan Kara , Andrew Morton , Zi Yan , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Kiryl Shutsemau , Matthew Brost , Joshua Hahn , Byungchul Park , Gregory Price , Ying Huang , Alistair Popple , Peter Xu , Johannes Weiner , Song Liu , Rik van Riel , Miklos Szeredi , Alexander Viro , Christian Brauner , Hugh Dickins , Will Deacon , "Aneesh Kumar K.V" , Nick Piggin , Peter Zijlstra , Arnd Bergmann , Jason Gunthorpe , Kevin Tian , "Joerg Roedel (AMD)" , Robin Murphy , Steve Sistare , John Hubbard , Josef Bacik Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, fuse-devel@lists.linux.dev, linux-arch@vger.kernel.org, iommu@lists.linux.dev, stable@vger.kernel.org References: <20261107-refcount_overflow_stable-v2-0-c38f6809b106@kernel.org> <20261107-refcount_overflow_stable-v2-5-c38f6809b106@kernel.org> Content-Language: en-US From: "Jose A. Perez de Azpillaga" In-Reply-To: <20261107-refcount_overflow_stable-v2-5-c38f6809b106@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 11/7/26 11:23 PM, David Hildenbrand (Arm) wrote: > Let's add a folio_ref_count_over_limit() check in fast and slow GUP > before acquiring additional references or pins. > > Keep it simple and use the check for all folio types. > > Don't check capabilities with IRQs disabled, as even unaudited capability > checks can take locks. Refuse access to the admin reserve, so GUP-fast will > fail and fall back to GUP-slow if possible. > > Also propagate try_grab_folio() errors when grabbing additional > references in __get_user_pages() and in memfd_pin_folios(), so hitting > the limit returns -ENOMEM instead of -EFAULT and -EINVAL, respectively. nice! > Keep the existing invalid-refcount warnings. > > Fixes: 800d8c63b2e9 ("shmem: add huge pages support") > Fixes: 99cb0dbd47a1 ("mm,thp: add read-only THP support for (non-shmem) FS") > Fixes: 793917d997df ("mm/readahead: Add large folio readahead") > Cc: stable@vger.kernel.org > Signed-off-by: David Hildenbrand (Arm) Reviewed-by: Jose A. Perez de Azpillaga -- cheers, jose a. p-a