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=1794235583; b=FySArSkUFDR1rE6AO+XcQR2DEsQdcf2siHhKwB4jRb215GdP8HFlE0GhCrfNBYZgfnfN at6k+Gcpdirxr83tn3iKW6uBxyJFsjj5M6Xg93sw6hm+d3nbExACYS/7Wicx3hqYSzDA5 piMl/gTvpP9rFf39U2PS5WoQFi2UpcQXeHyLFCNPLotVxfAjZJzqfVO5g9zja+DR9NF8Z gTcr6lkw4Pa9CqdAsIcKQkxc5Cl4gMpF7lQFvh2sXNvA8ysN3i7tPIvvafy4t60VDD+RQ +Ksi+S/iT22QO2xRdeBqZeNmDr91myDLaCx8IdY7hSJp1eRJDCoS+r/njNEoN/8yPhw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794235583; 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=93AR0ixWRF7Xc+mKq42uEUHnh202mM0USTi6ybrtt/0=; b=o35LYz1AqkQzhto2HS+5NQVYY2RDCXLRYR6fsK2MWKc2aJaFW2eotNe30OwK9EsgtWlt MK0Ye0oSLFq5pdewRyJowS6YAJauuMA0RGZWCDSlPzv9VuxwynA7xILYfkwzc9Qeyx5MT lAVmtPG43We3Glpoe5+swmnaG5hdSITj1XkVjOYtWV7yKEh1vnHBbbEIpXQK7QtGzlLGn gITE9nAqRaWWqiY3/mDwWZgW0+h/8F+IosDg1M5LvtGYkyjK9+nCEs9aBsTAafelaP0xJ kmPvVuSs3VjIDHIg/H6/GfOxTfCCoDr4oeaIButXwh4lpHbuxO30QmTwvOxwFhoIbaQ== 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=R3j5M1Gt; 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 1A155606A31C; Mon, 9 Nov 2026 14:46:23 +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=R3j5M1Gt Received: by smtp.kernel.org (Postfix) with ESMTPSA id 620B81F0089F; Mon, 9 Nov 2026 14:46:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794235583; bh=93AR0ixWRF7Xc+mKq42uEUHnh202mM0USTi6ybrtt/0=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=R3j5M1GtbQ4HJLT7OhpTZEh2BryQV+uiLHfcysgIOQ1NFb5i4bak6X+eNkP0EAbZ9 IQ85enPQ15w1I2aklY5dL5f+9UPF1nB4OWrbOipMU1EhxsV2QyXRhRi7HD89zlVrf2 7dp+w/hxXIYXChRG6Ji8VoQrIx+r53F4pKdzVlHCKuMaMejkxQ+1tOSwdkAJ62sF6h C72/0kQZRLR+UgfMObni0YgD7P8W7VFoxpbK2xToMWavoQI7CPAdxeSX5jQMqY0cW2 bIXVv9cTXdaGNcAZah1PVqO7mgk/LZXCLJk1Xgn4u2atOJoobfxWL1KjRB9VY6Ej/t Oj1Qw5V5yi4vg== Message-ID: Date: Mon, 9 Nov 2026 15:46:10 +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: [RFC PATCH v2 03/18] fuse: don't move a folio with PG_rcu_free into a fuse file To: "Kiryl Shutsemau (Meta)" , Andrew Morton , Linus Torvalds , Matthew Wilcox , Vlastimil Babka , Lorenzo Stoakes , Jan Kara , Hugh Dickins , Christian Brauner , Alexander Viro , Harry Yoo Cc: Miklos Szeredi , Miaohe Lin , Naoya Horiguchi , Oscar Salvador , "Liam R. Howlett" , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Johannes Weiner , Zi Yan , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Kairui Song , Qi Zheng , Shakeel Butt , Axel Rasmussen , Yuanchu Xie , Wei Xu , Baoquan He , "Paul E. McKenney" , Pedro Falcato , Luis Chamberlain , Ilya Gladyshev , Jaegeuk Kim , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, fuse-devel@lists.linux.dev, kernel-team@meta.com References: <20261104130118.2507513-1-kas@kernel.org> <20261104130118.2507513-4-kas@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: <20261104130118.2507513-4-kas@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 11/4/26 14:00, Kiryl Shutsemau (Meta) wrote: > fuse_try_move_folio() takes the folio of a pipe buffer and puts it into > a fuse file, where writes change it. A folio with PG_rcu_free may still > be copied by a lockless page cache read that found it before it left > the page cache. > > Such a folio reaches fuse when a mapped file page is gifted with > vmsplice(SPLICE_F_GIFT) and its file is then truncated. > fuse_check_folio() refuses it only because the flag is not among those > it allows, and with a dump_page(). > > Copy such a folio instead, as fuse does whenever it cannot take one. > > Signed-off-by: Kiryl Shutsemau (Meta) > --- > fs/fuse/dev.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c > index 4fec31fc0b84..526929c7b3f1 100644 > --- a/fs/fuse/dev.c > +++ b/fs/fuse/dev.c > @@ -1152,6 +1152,10 @@ static int fuse_try_move_folio(struct fuse_copy_state *cs, struct folio **foliop > > newfolio = page_folio(buf->page); > > + /* A lockless page cache read may still be copying from it */ > + if (folio_test_rcu_free(newfolio)) > + goto out_fallback_unlock; > + > folio_clear_uptodate(newfolio); > folio_clear_mappedtodisk(newfolio); Talking to Zi, it would actually be nice if we could disallow converting ordinary pages to folios and the other way around. That will be required for some future changes where we identify folios with a distinct PG_folio. Could we get rid of fuse_try_move_folio() entirely? I think we'd just want to get rid of any such stealing if possible. -- Cheers, David