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=1794217830; b=cCs4xqBGdO21vzg1k06vLOIBQpMLMeIbIHF8JGTIwJ+Z//M0W4Ee1x05z56/tnclEtos J1uNApD/XIlbo+jD3bm0bef85zIDD+iZ9MXYmFxFQi5kDAlU2C7wTyKcFxsQUvt6MoIXi E0r1WuEsRXz+rI/Iyxqm7Ni4DrvlxN+6jZjH8Nof/c4hsIrUk8TMAl5yfh0QCvxBZBK2A E4x4RVf5r8jNjo4mmtb8u5ozg2xxcuFi3Qdwi/82dCg/0E/OUMMEIZUmJdxqXEZXBznYC cxOeuCX9HKlhY8HA2BqJzyRR7ek29ADOYGIxT/BN+8CUrQ3WDPuAcyQtChAP7S7evuw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794217830; h=Received:DKIM-Signature:Message-ID:Date:MIME-Version:User-Agent: Subject:From:To:Cc:References:Content-Language:Autocrypt:In-Reply-To: Content-Type:Content-Transfer-Encoding; bh=8jQST5+SfU/stcEn1VOV+s+O2grX/AjdmKJu3mY8h/o=; b=Ej2fWZtB83gg5ecnot9hL7fjusmQvVPH4qbdBnpk+mTanNg/BT+xg+btl9BgAsHcfKqb DhXdrqkbU23WSnlQlXTyA0tg/RB1TBN8yTwoQkONBA1wr4rKKpYus9txgbcSdkcoPOOVP 1zhp5NiyqTw84T4AhLnI1KSsRhPXkrb6TjIA8UF+o698Cf9M9nM5hxo2v9cfqLvWTKWNh HfJnpSnjV3e/ZreZoUSKAxQCXtmQXfkW60jZ8HDvj4nWmCHWaGZQiMS0JukonmJuMsA/Q 5z+XfOGLkwVCh6KMnX1Q7GjGdkOvwNbkao1kukVfBoWc0aDVjdlNI+MkgnQ9l3a//0w== 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=OvHIGFuz; 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 60E19606A321; Mon, 9 Nov 2026 09:50:30 +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=OvHIGFuz Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9AB921F0089F; Mon, 9 Nov 2026 09:50:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794217829; bh=8jQST5+SfU/stcEn1VOV+s+O2grX/AjdmKJu3mY8h/o=; h=Date:Subject:From:To:Cc:References:In-Reply-To; b=OvHIGFuzeTrht0qsWVugipKYTrQLZcnvB6H9AoSgt/BfQa9OPyUvWqvJ8MOIsDadM GanFXxKFurEMX1AJqRVtXq3aRWMU3f5+WrFTpo5wgIB//RmeuK1DCmhhBP23ms4Q1h OxpyKGhtol4qDQfjdGC5xXV4KMT4/NcBlPfpG7uNWKEuNcRlrmaMThNfOOIhb6iqsV 6bvrPZ4Od2X8Yz8iIIBCfsyQcB4XJmpr+4JPhTB/o49dc/swkETYACw1k9TwnUEdPS i/WrVh9yir+LZOUj1ItLVGLUb1Oim+AfBYVUIRuwBzAMFlgA47kPNAltSH3lzQo+Vl sFPz+2VdU0FGg== Message-ID: <43fc45ff-8636-4961-a80a-29844c15d7a1@kernel.org> Date: Mon, 9 Nov 2026 10:49:08 +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 2/5] mm: limit pagecache folio refcount when splicing into pipes From: "David Hildenbrand (Arm)" To: "Jose A. Perez de Azpillaga" , 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-v2-2-c38f6809b106@kernel.org> <8d23b1eb-72aa-479d-9486-dbfd86d8414c@kernel.org> 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: <8d23b1eb-72aa-479d-9486-dbfd86d8414c@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 11/9/26 10:30, David Hildenbrand (Arm) wrote: > On 11/9/26 09:57, Jose A. Perez de Azpillaga wrote: >> On 11/7/26 11:23 PM, David Hildenbrand (Arm) wrote: >>> Similar to mapping pagecache folios into page tables, let's reject >>> additional references when splicing folios into a pipe if the refcount >>> is at its limit, similar to how we handle it during GUP. >>> >>> This will prevent more cases of possible folio refcount overflows with >>> large pagecache folios. >>> >>> Let's keep it simple and check in the two callers of >>> splice_folio_into_pipe(). Return -EOVERFLOW if the limit prevents any >>> progress, so do_splice_read() can fall back to copy_splice_read() when >>> read_iter is available. This keeps sendfile() and other splice users >>> working when ordinary reads would still succeed. >>> >>> Also fall back to copying in FUSE when taking another reference through >>> fuse_ref_folio() would exceed the limit. >>> >>> Also check in try_get_page() to cover pipe-buffer duplication by tee() >>> and partial pipe-to-pipe splicing. >>> >>> 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) >>> --- >>> fs/fuse/dev.c | 5 +++-- >>> fs/splice.c | 8 +++++++- >>> include/linux/mm.h | 9 ++++++--- >>> mm/filemap.c | 11 ++++++++--- >>> mm/shmem.c | 4 ++++ >>> 5 files changed, 28 insertions(+), 9 deletions(-) >>> >>> diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c >>> index 3641abb90d6bb..4f6b7b42bfd3e 100644 >>> --- a/fs/fuse/dev.c >>> +++ b/fs/fuse/dev.c >>> @@ -1265,9 +1265,10 @@ int fuse_copy_folio(struct fuse_copy_state *cs, struct folio **foliop, >>> if (cs->write && cs->pipebufs && folio) { >>> /* >>> * Can't control lifetime of pipe buffers, so always >>> - * copy user pages. >>> + * copy user pages. Also copy folios at their refcount limit. >>> */ >>> - if (cs->req->args->user_pages) { >>> + if (cs->req->args->user_pages || >>> + unlikely(folio_ref_count_over_limit(folio))) { >>> err = fuse_copy_fill(cs); >>> if (err) >>> return err; >>> diff --git a/fs/splice.c b/fs/splice.c >>> index e6d43329ed3f0..df73a4e65118b 100644 >>> --- a/fs/splice.c >>> +++ b/fs/splice.c >>> @@ -956,6 +956,7 @@ static ssize_t do_splice_read(struct file *in, loff_t *ppos, >>> unsigned int flags) >>> { >>> unsigned int p_space; >>> + ssize_t ret; >>> >>> if (unlikely(!(in->f_mode & FMODE_READ))) >>> return -EBADF; >>> @@ -977,7 +978,12 @@ static ssize_t do_splice_read(struct file *in, loff_t *ppos, >>> */ >>> if ((in->f_flags & O_DIRECT) || IS_DAX(in->f_mapping->host)) >>> return copy_splice_read(in, ppos, pipe, len, flags); >>> - return in->f_op->splice_read(in, ppos, pipe, len, flags); >>> + ret = in->f_op->splice_read(in, ppos, pipe, len, flags); >>> + >>> + /* Fallback to copying when hitting folio refcount limits. */ >>> + if (unlikely(ret == -EOVERFLOW) && in->f_op->read_iter) >>> + ret = copy_splice_read(in, ppos, pipe, len, flags); >> >> here it can't tell where the -EOVERFLOW came from, if another file >> returns -EOVERFLOW (i.e. tty_fops uses copy_splice_read, and >> n_hdlc_tty_read() returns -EOVERFLOW after dropping the frame), it now >> gets a second read. > > > That's what claude told me during review, and when asked whether that actually > happened in practice it said no ;) > > So is that actually a problem? Double checked, claude managed to confuse itself. n_hdlc_tty_read() can indeed return -EOVERFLOW. I should just have let splice keep failing, dealing with copy fallback starts to get annoying. I guess switching to -ETOOMANYREFS should work (and might be a better fitting error) -- Cheers, David