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=1794225195; b=Q50J2dIddDzjDGdRyzC122VnNJIlFUJEKCyjgirJBK932tfXDv5aScwPjuweWpzthvqf vLIh7g9ad0ZXUUaoFTUUQzM2R63u4WZYLjZgbwXlyRlirrrL/OYNsEVCMerwd1cb03sMw rgYy+6NKJOWPhOZWeTl8K3IS8BW8Aub6S7VilJMJHNY0X9Iei0PPjodEPA7MRxzwT0Ms8 GrfFCc/9kaqYW6wMkXr7UOBoiOb69pSU6XmWLXsxUdIMuJgB23aN7inoe8L8sDI2ygB7Y meSEN+tV0fsYNYuWwK1T885HVIsPybLQkpa+A2I07T0Ex+jdk8A73A/KV5JEt78iCQQ== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794225195; 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=JoZ3JKHOn0R0njHxsO6/Qrtb22qc0xZhgECNmIgLvRg=; b=235H4TeOFuT0J2oB97Doxw1ztksiQqLbJdrvHpL9QRymGKgCfeMUt6Y8SWvv2XluieEc vwb/G2Icxh/2qwG0s8tRPuX0x0I6EQNIEqWNdqBUVUmHBga7wirq+JORb9CWTb+UOMI+P aQaHcQsSfm3Snwz5g/trIr5hp/as3KtWQiAJCTVNmV0jHPL+WCSNAQZKbqP30js+zO1/E BlEwZPpnW9LSq1f+q5ixiIGvGzZVJ0qMZsZTF5gBkHRqe3a0tM/1NTC1xXYxfRHfgQ4L/ Ej4MGWT53AUOMpErFst3Ubu6ZttAxQVIaovuaxny5w0/mrRsxoo227oZBrt68+rb6nw== 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=V7BzJ8S0; 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 196BE606A31C; Mon, 9 Nov 2026 11:53:14 +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=V7BzJ8S0 Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8ACCB1F008A4; Mon, 9 Nov 2026 11:53:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794225194; bh=JoZ3JKHOn0R0njHxsO6/Qrtb22qc0xZhgECNmIgLvRg=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=V7BzJ8S07RSb3MVWSX5A3mbdbydBpHaRs75Gx8FoqdNI9rvRIUC/2Hhdy95BDtlLU 6A90zI4LH+N8rPi52yQTMi9HirA5d/lkjGiWD92nXjl9V3/CLq2UgbCSWkQNpXZzuB Cunq+r5k1AYrwWV18+paxZbnuL4SpjKS07Hs9v/JQLeUbF2Ucgpr6CSp9RdbOwHM08 WBF1Jjuz/y90oj6uKQvQUwCjhQ7BHkVaSU0rXqdI/CNNxlBFqwJ5jsjSsq0F4K1jIu eqFBvmGbIqxGkosJaV32QP2goyQtgAKf4lSlHEi9fkYzf9c46H2EaF3EwcNhI4pAW3 5NR3fA883aOTQ== Message-ID: <66590b61-6538-4200-8de9-68b2e1d2c697@kernel.org> Date: Mon, 9 Nov 2026 12:52:58 +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 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> <43fc45ff-8636-4961-a80a-29844c15d7a1@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 11/9/26 11:25, Jose A. Perez de Azpillaga wrote: > On 11/9/26 11:08 AM, David Hildenbrand (Arm) wrote: >> On 11/9/26 10:49, David Hildenbrand (Arm) wrote: >>> >>> 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) >> >> Yeah, the following should do I think, please double check: >> >> From 7ce030711737e8c26fb5500f2705940e93da0d44 Mon Sep 17 00:00:00 2001 >> From: "David Hildenbrand (Arm)" >> Date: Wed, 4 Nov 2026 19:02:48 +0100 >> Subject: [PATCH] mm: limit pagecache folio refcount when splicing into pipes >> >> 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 -ETOOMANYREFS 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..2fc1279628af5 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 == -ETOOMANYREFS) && in->f_op->read_iter) >> + ret = copy_splice_read(in, ppos, pipe, len, flags); >> + return ret; >> } >> >> /** >> diff --git a/include/linux/mm.h b/include/linux/mm.h >> index 3356f7a670d1e..dd50262a70758 100644 >> --- a/include/linux/mm.h >> +++ b/include/linux/mm.h >> @@ -2288,10 +2288,13 @@ static inline void get_page(struct page *page) >> >> static inline __must_check bool try_get_page(struct page *page) >> { >> - page = compound_head(page); >> - if (WARN_ON_ONCE(page_ref_count(page) <= 0)) >> + struct folio *folio = page_folio(page); >> + >> + if (WARN_ON_ONCE(folio_ref_count(folio) <= 0)) >> return false; >> - page_ref_inc(page); >> + if (unlikely(folio_ref_count_over_limit(folio))) >> + return false; >> + folio_ref_inc(folio); >> return true; >> } >> >> diff --git a/mm/filemap.c b/mm/filemap.c >> index 920bbf86dfdff..44b23c51ea45f 100644 >> --- a/mm/filemap.c >> +++ b/mm/filemap.c >> @@ -3094,9 +3094,10 @@ size_t splice_folio_into_pipe(struct pipe_inode_info *pipe, >> * Return: On success, the number of bytes read will be returned and *@ppos >> * will be updated if appropriate; 0 will be returned if there is no more data >> * to be read; -EAGAIN will be returned if the pipe had no space, and some >> - * other negative error code will be returned on error. A short read may occur >> - * if the pipe has insufficient space, we reach the end of the data or we hit a >> - * hole. >> + * other negative error code will be returned on error; -ETOOMANYREFS will be >> + * returned if the folio's refcount is too high and the caller can fall back to >> + * copying. A short read may occur if the pipe has insufficient space, we reach >> + * the end of the data or we hit a hole. >> */ >> ssize_t filemap_splice_read(struct file *in, loff_t *ppos, >> struct pipe_inode_info *pipe, >> @@ -3168,6 +3169,10 @@ ssize_t filemap_splice_read(struct file *in, loff_t *ppos, >> if (writably_mapped) >> flush_dcache_folio(folio); >> >> + if (unlikely(folio_ref_count_over_limit(folio))) { >> + error = -ETOOMANYREFS; >> + goto out; >> + } >> n = min_t(loff_t, len, isize - *ppos); >> n = splice_folio_into_pipe(pipe, folio, *ppos, n); >> if (!n) >> diff --git a/mm/shmem.c b/mm/shmem.c >> index be4ab228cf67c..0b30b1de81a7c 100644 >> --- a/mm/shmem.c >> +++ b/mm/shmem.c >> @@ -3830,6 +3830,10 @@ static ssize_t shmem_file_splice_read(struct file *in, loff_t *ppos, >> * Ok, we have the page, and it's up-to-date, so we can >> * now splice it into the pipe. >> */ >> + if (unlikely(folio_ref_count_over_limit(folio))) { >> + error = -ETOOMANYREFS; >> + break; >> + } >> n = splice_folio_into_pipe(pipe, folio, *ppos, part); >> folio_put(folio); >> folio = NULL; > > this LGTM :) Thanks! -- Cheers, David