From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794493914; b=nk6XsJv0RQXl6vKy3B2CBueG3HscdiK3OApOvkAGkTKfwXxWCg0Y+LjaX9AVKlXTC6NU DN4MSC3whYh63y+L7Dn7D0+n6381tYufVTTRJOEbOh/u/7Q4QRfrEI7M2T8StXOhlmOWE ihQSTdiIthMfg+9HAU0s7ViqHg2gcefBW2LCrip8UV+nOZrssGECAxJQ4rwOgLu4ZRDSo stxsljNumN0nrjFht8Eb3luO9a8msFyMWBShEnr0Xw1ANh1tSB90aTVPLmyP8vYJx/WcK 1HuOH7HCOJoYhDlaGJC676uwKYe2Y/UqiyHQo74ELY4l0kR4ua4NI5nBjYYiinLxGnQ== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794493914; h=Received:DKIM-Signature:Message-ID:Date:MIME-Version:User-Agent: Subject:To:Cc:References:From:Content-Language:Autocrypt:In-Reply-To: Content-Type:Content-Transfer-Encoding; bh=qL8uHuX3QnsZ5VDS6Dz7mGSNJ+Qw6vdd/slrMNoAIKA=; b=YJDJihalYIvWXQNLDQn4s3xl5ln/6xMB4DzLQAIA8V8GBKV1CstbqLFWBWtNYEa0Ph2p TE/n1uNSYmPkAHX//7W/Ea/Pp7ggnbpcJdb5XUIwV9wGcKXiPr37hB3LQ7SCbQL1RRp3V bvi7ji4QeGpsYY3BCwgMxpRP9wSePbGSl35fbM9fa0R3fwcuJlMWMa7CuiCbcBt16LkPu eUodpytMD0+cLOs2k6EuhVKF0k3/0uh8uNNMyjCQJX1BCal3wvJt2uM5Wy+gvGVvoREf9 PrIaPiBq8VEz5k+R3joJGjoFA6lfE8HfvRZ21rvoDXnuVWsRmBrqzZlDA9GHhO5LNsA== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=GPJGh0mQ; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9F572606A76B; Thu, 12 Nov 2026 14:31:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=GPJGh0mQ Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6ED0B1F00A07; Thu, 12 Nov 2026 14:31:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794493914; bh=qL8uHuX3QnsZ5VDS6Dz7mGSNJ+Qw6vdd/slrMNoAIKA=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=GPJGh0mQr0iIywi1xK6YGtM++LzH5gKmiwWRk/EnY73REob9IoY6kKD2kjRit5NuQ qpCKoyGF5evmVOqDiFdO/iBXzFsGJNLGlbHO3xqyGfKWmUja0mkc+JARlV67F/VS3m ED8MuOYLsOkzOwLBf6PijVRAwyXOxIrEDHRTccN8Sx/5xthxqNLDxaI+qVDumcKzXu HH1oLUtanfgtu8dIToH107vmYlhQRsztMYYGF4hLaV0DBLVBZCWZjkRgq/I+0Ad/k0 vZo0ZM0g2a9yHKmcZVucd0nDe9FvVQBR8Be5TI13/KkoP9N6fNDEN3H7l1nZd5V0p4 7FchAVT3ZPcjQ== Message-ID: <42373222-8e37-4658-bebd-dd27230a1dfa@kernel.org> Date: Thu, 12 Nov 2026 15:31:30 +0100 X-Mailing-List: netdev@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 v3 2/9] mm: limit pagecache folio refcount when splicing into pipes To: Pedro Falcato Cc: 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 , "Jose A. Perez de Azpillaga" , Josef Bacik , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Neal Cardwell , Kuniyuki Iwashima , Linus Torvalds , 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, netdev@vger.kernel.org, stable@vger.kernel.org References: <20261110-refcount_overflow_stable-v3-0-318625d63a98@kernel.org> <20261110-refcount_overflow_stable-v3-2-318625d63a98@kernel.org> <4ae22b7a-c160-4003-a029-8a20381d196f@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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 B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+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: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 11/12/26 15:00, Pedro Falcato wrote: > On Thu, Nov 12, 2026 at 02:24:09PM +0100, David Hildenbrand (Arm) wrote: >> On 11/12/26 14:09, Pedro Falcato wrote: >> >> [...] >>> >>> -EFAULT is a weird error code to return from splice, et al. >> >> We might be able to use ETOOMANYREFS (have to check if that could confuse >> callers), but IMHO EFAULT is good enough. >> >> What would be your suggestion? > > ETOOMANYREFS I think is good, also EBUSY, EMLINK (though this would be weird) > or even a generic -EIO. So I used EFAULT because that's also what we currently return when generic_pipe_buf_get() fails through pipe_buf_get() in splice_pipe_to_pipe() and link_pipe(). If we want to return ETOOMANYREFS we'd likely have to special-case "<= 0" ref count and things get more complicated, as we'd have to return two different error cases. And then we'd still have the inconsistency with the above cases. I'll mention that I do not expect that we can trigger overflows in any reasonable setup once we changed the way page table mappings are refcounted. So for consistency with the existing checks I'd leave it at -EFAULT for now. > >> >>> >>> return spliced ?: -EFAULT; >>> >>> I don't know if there's much kernel code out there doing this, but I like >>> the trick :) >> >> There are a couple of thousands, but yes, one doesn't encounter it that often. >> >>> >>> >>> I'm confused. Why does this need to be done here? >>> >> >> I have above: >> >> "stop filemap_splice_read() if we only spliced part of a folio, so we don't >> skip ahead to the next folio" > > Yes, but is this a separate fix? A folio could be partially spliced previously > as well, no? I think that wasn't possible because splice_folio_to_pipe() never returned early. So it's only possible now once we fail to splice halfway through. > >> >> Thanks a lot for the review! > > You're welcome! :) > > FWIW, you can add my > > Reviewed-by: Pedro Falcato > > to whatever comes out of these nits :) Thanks! :) -- Cheers, David