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=1793995765; b=L9lApsakdUsF3VHRzWMnKrAS3zq83RBSiPBC3XymH9NQf1eqwxBIGN7NM0JdlfOA2wRa hqV/Cjrl/Uh2lXNksT6BIc0Uh1PAW5sppKTNnjbHFnekrdkGjF9AlSX9eOgAdC/US+w+i wKmD6CBmR6SdQ+HLPKyJ86jPj5F6nWWvQxN5c5/mnUtpeIdO264RZJG0hOB4qTqmP6UZ1 LmmQY4JCgM9WK3zP2n8WE2mZmrkTYkTA8aB+SfqIDoE7vQDvms2lXjH56zQhnWkuXsYry hf7VACSiABYX310vMDTs0hlzFxHx+n/tmT0Y5o0OKqBh5PaPjSX6+TxdfGNYTVELfEA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793995765; 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=QYKpj50QcPFYT5hlR28ZO7Qz7JK2NgENQ8jSUlp2pWU=; b=0/8whyqYFl82TwtRjbGLj8DbOlzcIB1a8NZyj1i+MOvNfa0RefDYQCjM/Cx3wlaY/qLf mgWc94m23nSP1quN2K9m3uQhg7o3ubFQkiz+wKkw7gg5FTfb/Rb52I6XGyTjTMkkGOvqH /dut6VjPu6NbV3+KXY71IQwe2m4zqH8RMOeu4OIPjoecoobILfNvfpXWcxsFEdD2ce3RI AkBp7AWrD9b0YkfxNDNQXYnQFTecKsOcR3HWpMns/oZ+56kWf86HxcJmnxhKi/qBArrw3 hp5bMVjuuqxk57mhN/yTOCj6eloDnVaPBpSXcYKrbFsnO4o31RVD2p3pL8LXmMHbPfQ== 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=YrVHuq3J; 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 D3496606A326; Fri, 6 Nov 2026 20:09:24 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=YrVHuq3J Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0EA0E1F0089F; Fri, 6 Nov 2026 20:09:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793995764; bh=QYKpj50QcPFYT5hlR28ZO7Qz7JK2NgENQ8jSUlp2pWU=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=YrVHuq3JuRIEd7tjBfUeT/Qk0DuNfXl4YVMThJcT80ptmZzANGzEFsALP5sxZlfys ZABuxRNId9i2ezwIzNGhupGpPTeG/+Ua0IrtHAZyldbRgEphdzF0p3FPQ7z2zoF1kn nnpyFnX40vBIUYmViW8+50dWaKQ2zK/tAClXS4kmgJtUsTS0KOxjpN86eOoHQVGSep mHAXwv6xOdHMx1KYuOPXddB6d1cGWA8dfX7t2r/bAOguAP/l+m6+jUWmmCYirJz51i p+FWCDRFD6IkmQ3s3PTHPzmFC44LSnKdiFht+QMqWssMW7YWrzR8NFKdbo6HzPrjQq e3DYi6gFzU+wg== Message-ID: <23f947e2-ff06-426d-adb7-396871304736@kernel.org> Date: Fri, 6 Nov 2026 21:09:10 +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 2/5] mm: limit pagecache folio refcount when splicing into pipes To: Josef Bacik Cc: Andrew Morton , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , "Matthew Wilcox (Oracle)" , Jan Kara , 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 , Hugh Dickins , Will Deacon , "Aneesh Kumar K.V" , Nick Piggin , Peter Zijlstra , Jason Gunthorpe , Kevin Tian , "Joerg Roedel (AMD)" , Robin Murphy , Steve Sistare , John Hubbard , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org, iommu@lists.linux.dev, stable@vger.kernel.org References: <20261105-refcount_overflow_stable-v1-0-70b9c655da3e@kernel.org> <20261105-refcount_overflow_stable-v1-2-70b9c655da3e@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 11/6/26 18:58, Josef Bacik wrote: > On Thu, Nov 05, 2026 at 02:10:11PM +0100, David Hildenbrand (Arm) wrote: >> Similar to mapping pagecache folios into page tables, let's reject splicing >> folios into a pipe if the refcount is at it's 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(). >> >> 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) >> --- >> include/linux/mm.h | 9 ++++++--- >> mm/filemap.c | 4 ++++ >> mm/shmem.c | 4 ++++ >> 3 files changed, 14 insertions(+), 3 deletions(-) >> >> diff --git a/include/linux/mm.h b/include/linux/mm.h >> index 79ae8fc0d6bb4..a82cfbce18215 100644 >> --- a/include/linux/mm.h >> +++ b/include/linux/mm.h >> @@ -2287,10 +2287,13 @@ 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)) > > Since you're here anyway can you change this to something other than > WARN_ON_ONCE, since that results in an OOPS with panic_on_warn set? > Thanks, If it actually turns negative (or 0) with out changes, we had an overflow and for sure want to know about it :) -- Cheers, David