From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 21A3E22F77B for ; Wed, 17 Sep 2025 14:52:50 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758120773; cv=none; b=AmXURZgEwAMfyoMtcC1Aky9hVggr+Z20jc1jfLxgkG6Jjo9I/U4zaYL+E32f855+ZDL8EceEuGzxjLPUZgv28xcL8+Jla2TD6tR+rP3sQuOIqBdQ9NUJ0pbcqWSlg94dUljXb8gwTgcgdtystQBK6rwcslX3H4fA4+R0/cxZzK8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758120773; c=relaxed/simple; bh=5epPT/yF5ySKt5yJiiDB0pyPwiJwOtudKK0nsTblkcQ=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=A8HlJuhhhlqTqTYBBatvzaWeN5ZdiW4vCr+wJb+mOUgn34A/ZOlNcRyXNDmYfgaZTws7GSSuRbkfA7YquF4i7zEioCjdSPA2o/C1hJBBOpnqY/axEYAe2w0gotro/4wzLhnKrSrCHAUe2Uyyu2rR9/ZSsMVXKVVdd1r5hQvFm7s= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=S6Dkz3LX; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="S6Dkz3LX" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1758120770; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:autocrypt:autocrypt; bh=gDs3CUgjimStalCZ6Y06kSWDcmRW5MkZeDVBa3itpks=; b=S6Dkz3LXgmThNV1KGKLbxrk8dDCTr/qYg30mv9vyF3qAZhCYeqcQExUSqaFyszHisV5rAN 76gOws2XJXaTQG3daBAMlMzHJfO3NXGCCMp+S4b5f+VS8U3pJO1SBhNM8S0kj2IkQqJjNl CGci2eNzc5W8i3OO1Izzu28xKjcC468= Received: from mail-wr1-f72.google.com (mail-wr1-f72.google.com [209.85.221.72]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-453-7-0HV-30PXKZ1hbb1UDzqg-1; Wed, 17 Sep 2025 10:52:48 -0400 X-MC-Unique: 7-0HV-30PXKZ1hbb1UDzqg-1 X-Mimecast-MFC-AGG-ID: 7-0HV-30PXKZ1hbb1UDzqg_1758120768 Received: by mail-wr1-f72.google.com with SMTP id ffacd0b85a97d-3eb8e43d556so443552f8f.1 for ; Wed, 17 Sep 2025 07:52:48 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1758120767; x=1758725567; h=content-transfer-encoding:in-reply-to:autocrypt:content-language :from:references:cc:to:subject:user-agent:mime-version:date :message-id:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=gDs3CUgjimStalCZ6Y06kSWDcmRW5MkZeDVBa3itpks=; b=W/Lb5KLEUHJITD4FuicI2HStWym/JKO8gsbt5DsRO1XVz5cwBHu7JZPO5TWJ9yvU/p +pHdMy61cb3d/rAQBunOVZGrmOi65YbPVU+iZfTd1k8pqN71Gf9s4B+nYo8mh+IiGKS9 d4wHLnkSA/sOwb23g2oAPYVOLFvri11T6MtMmaQtBd/ULRNsDznA5O0WsLxPbIeF+WVO GLNPVIQNOEK85BAqfElJET/Z8vZrUjueOtwm4JWVSURKLjVfDJjIidg9iJyQfdCuksao bPGt312dLXgGQdh655C8ZQKu8k8u8L0z82GL5RRh8SeWNG1zwaOupTrqOUeJ84af+H6b oRXg== X-Forwarded-Encrypted: i=1; AJvYcCXKgp7z+dB5CgX0sTK7HKG/sXju9z/RlHvzfHmvNzAaug2J8/Bi2vYagwiX30ce7CkrC+e5qrB236S1O6g=@vger.kernel.org X-Gm-Message-State: AOJu0YwZJdXtm7ZqsqXx9MKQtXRjnmKREID9FwLvczR/ld0ygSLMZLb0 8o+S2uKbcDFQuYzIjQx/IkeYzlxaNZRgebbn+aXh/faIj/ho3cowHUXGiWCqZk8A3QFER9P1GWQ wEE+CYMcjGs1kHTztvwUJA5MOk451liXVU0EXuPrVlfOHO9ONr0JUSo2NVp1aXOJy6Q== X-Gm-Gg: ASbGncvGny8v+Sdjb8xv0hUpOYym1ouN/ifCMxRLb0sY3EdhjM5l72HSrIeMKPrN9Fw nnnFZrYXm/r6O4FG5zGLSgzRLZmaVSeoNz0PZAlI6VjlagZVUvAqNRQqo9h4o6FC1bCfixEkl0R txQ+GRd5eOwmMRdrKlfwV/flK8nOORbTkyc5OxrpCv3XnOfb9CfIILO6+DllSP3qGBiZmKpejFP MRx0ugMWGHAnd6uMkYINAj+O7FPITzLvyJb7w06jKkoOPuOYABji3I9R4kREMjQwCA2w86nrRWh eJiW59WC3kLd/55mo55F2CgliLJoxlzDGR8TVZ9xRn+4rRI+tE1qOR9S5X8U5R/goJhtjCCETa4 y/2/knGGKosP8LoaaPQPMvtaj117QZlVH6IHAxD7LOA3RyeD9rteqJrR8SfVCploT X-Received: by 2002:a5d:584d:0:b0:3ea:d634:1493 with SMTP id ffacd0b85a97d-3ec9d70e1aemr6331373f8f.3.1758120767174; Wed, 17 Sep 2025 07:52:47 -0700 (PDT) X-Google-Smtp-Source: AGHT+IHCVwA2whdJvJ6k0SNSXVgRVBCXXeS7K5H+4SZxMmaPtCI7Uv2obWcxbuvE8IbcU5jjC+Gugg== X-Received: by 2002:a5d:584d:0:b0:3ea:d634:1493 with SMTP id ffacd0b85a97d-3ec9d70e1aemr6331269f8f.3.1758120766367; Wed, 17 Sep 2025 07:52:46 -0700 (PDT) Received: from ?IPV6:2003:d8:2f27:6d00:7b96:afc9:83d0:5bd? (p200300d82f276d007b96afc983d005bd.dip0.t-ipconnect.de. [2003:d8:2f27:6d00:7b96:afc9:83d0:5bd]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4613f3c69d5sm39701795e9.24.2025.09.17.07.52.41 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 17 Sep 2025 07:52:45 -0700 (PDT) Message-ID: Date: Wed, 17 Sep 2025 16:52:40 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6 01/11] filemap: Pass address_space mapping to ->free_folio() To: Hugh Dickins , "Roy, Patrick" Cc: "Thomson, Jack" , "Kalyazin, Nikita" , "Cali, Marco" , "derekmn@amazon.co.uk" , Elliot Berman , "willy@infradead.org" , "corbet@lwn.net" , "pbonzini@redhat.com" , "maz@kernel.org" , "oliver.upton@linux.dev" , "joey.gouly@arm.com" , "suzuki.poulose@arm.com" , "yuzenghui@huawei.com" , "catalin.marinas@arm.com" , "will@kernel.org" , "chenhuacai@kernel.org" , "kernel@xen0n.name" , "paul.walmsley@sifive.com" , "palmer@dabbelt.com" , "aou@eecs.berkeley.edu" , "alex@ghiti.fr" , "agordeev@linux.ibm.com" , "gerald.schaefer@linux.ibm.com" , "hca@linux.ibm.com" , "gor@linux.ibm.com" , "borntraeger@linux.ibm.com" , "svens@linux.ibm.com" , "dave.hansen@linux.intel.com" , "luto@kernel.org" , "peterz@infradead.org" , "tglx@linutronix.de" , "mingo@redhat.com" , "bp@alien8.de" , "x86@kernel.org" , "hpa@zytor.com" , "trondmy@kernel.org" , "anna@kernel.org" , "hubcap@omnibond.com" , "martin@omnibond.com" , "viro@zeniv.linux.org.uk" , "brauner@kernel.org" , "jack@suse.cz" , "akpm@linux-foundation.org" , "lorenzo.stoakes@oracle.com" , "Liam.Howlett@oracle.com" , "vbabka@suse.cz" , "rppt@kernel.org" , "surenb@google.com" , "mhocko@suse.com" , "ast@kernel.org" , "daniel@iogearbox.net" , "andrii@kernel.org" , "martin.lau@linux.dev" , "eddyz87@gmail.com" , "song@kernel.org" , "yonghong.song@linux.dev" , "john.fastabend@gmail.com" , "kpsingh@kernel.org" , "sdf@fomichev.me" , "haoluo@google.com" , "jolsa@kernel.org" , "jgg@ziepe.ca" , "jhubbard@nvidia.com" , "peterx@redhat.com" , "jannh@google.com" , "pfalcato@suse.de" , "axelrasmussen@google.com" , "yuanchu@google.com" , "weixugc@google.com" , "hannes@cmpxchg.org" , "zhengqi.arch@bytedance.com" , "shakeel.butt@linux.dev" , "shuah@kernel.org" , "seanjc@google.com" , "linux-fsdevel@vger.kernel.org" , "linux-doc@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "kvm@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , "kvmarm@lists.linux.dev" , "loongarch@lists.linux.dev" , "linux-riscv@lists.infradead.org" , "linux-s390@vger.kernel.org" , "linux-nfs@vger.kernel.org" , "devel@lists.orangefs.org" , "linux-mm@kvack.org" , "bpf@vger.kernel.org" , "linux-kselftest@vger.kernel.org" References: <20250912091708.17502-1-roypat@amazon.co.uk> <20250912091708.17502-2-roypat@amazon.co.uk> <7c2677e1-daf7-3b49-0a04-1efdf451379a@google.com> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; 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 B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZoEEwEIAEQCGwMCF4ACGQEFCwkIBwICIgIG FQoJCAsCBBYCAwECHgcWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaJzangUJJlgIpAAKCRBN 3hD3AP+DWhAxD/9wcL0A+2rtaAmutaKTfxhTP0b4AAp1r/eLxjrbfbCCmh4pqzBhmSX/4z11 opn2KqcOsueRF1t2ENLOWzQu3Roiny2HOU7DajqB4dm1BVMaXQya5ae2ghzlJN9SIoopTWlR 0Af3hPj5E2PYvQhlcqeoehKlBo9rROJv/rjmr2x0yOM8qeTroH/ZzNlCtJ56AsE6Tvl+r7cW 3x7/Jq5WvWeudKrhFh7/yQ7eRvHCjd9bBrZTlgAfiHmX9AnCCPRPpNGNedV9Yty2Jnxhfmbv Pw37LA/jef8zlCDyUh2KCU1xVEOWqg15o1RtTyGV1nXV2O/mfuQJud5vIgzBvHhypc3p6VZJ lEf8YmT+Ol5P7SfCs5/uGdWUYQEMqOlg6w9R4Pe8d+mk8KGvfE9/zTwGg0nRgKqlQXrWRERv cuEwQbridlPAoQHrFWtwpgYMXx2TaZ3sihcIPo9uU5eBs0rf4mOERY75SK+Ekayv2ucTfjxr Kf014py2aoRJHuvy85ee/zIyLmve5hngZTTe3Wg3TInT9UTFzTPhItam6dZ1xqdTGHZYGU0O otRHcwLGt470grdiob6PfVTXoHlBvkWRadMhSuG4RORCDpq89vu5QralFNIf3EysNohoFy2A LYg2/D53xbU/aa4DDzBb5b1Rkg/udO1gZocVQWrDh6I2K3+cCs7BTQRVy5+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: <7c2677e1-daf7-3b49-0a04-1efdf451379a@google.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 16.09.25 08:23, Hugh Dickins wrote: > On Fri, 12 Sep 2025, Roy, Patrick wrote: > >> From: Elliot Berman >> >> When guest_memfd removes memory from the host kernel's direct map, >> direct map entries must be restored before the memory is freed again. To >> do so, ->free_folio() needs to know whether a gmem folio was direct map >> removed in the first place though. While possible to keep track of this >> information on each individual folio (e.g. via page flags), direct map >> removal is an all-or-nothing property of the entire guest_memfd, so it >> is less error prone to just check the flag stored in the gmem inode's >> private data. However, by the time ->free_folio() is called, >> folio->mapping might be cleared. To still allow access to the address >> space from which the folio was just removed, pass it in as an additional >> argument to ->free_folio, as the mapping is well-known to all callers. >> >> Link: https://lore.kernel.org/all/15f665b4-2d33-41ca-ac50-fafe24ade32f@redhat.com/ >> Suggested-by: David Hildenbrand >> Acked-by: David Hildenbrand >> Signed-off-by: Elliot Berman >> [patrick: rewrite shortlog for new usecase] >> Signed-off-by: Patrick Roy >> --- >> Documentation/filesystems/locking.rst | 2 +- >> fs/nfs/dir.c | 11 ++++++----- >> fs/orangefs/inode.c | 3 ++- >> include/linux/fs.h | 2 +- >> mm/filemap.c | 9 +++++---- >> mm/secretmem.c | 3 ++- >> mm/vmscan.c | 4 ++-- >> virt/kvm/guest_memfd.c | 3 ++- >> 8 files changed, 21 insertions(+), 16 deletions(-) >> >> diff --git a/Documentation/filesystems/locking.rst b/Documentation/filesystems/locking.rst >> index aa287ccdac2f..74c97287ec40 100644 >> --- a/Documentation/filesystems/locking.rst >> +++ b/Documentation/filesystems/locking.rst >> @@ -262,7 +262,7 @@ prototypes:: >> sector_t (*bmap)(struct address_space *, sector_t); >> void (*invalidate_folio) (struct folio *, size_t start, size_t len); >> bool (*release_folio)(struct folio *, gfp_t); >> - void (*free_folio)(struct folio *); >> + void (*free_folio)(struct address_space *, struct folio *); >> int (*direct_IO)(struct kiocb *, struct iov_iter *iter); >> int (*migrate_folio)(struct address_space *, struct folio *dst, >> struct folio *src, enum migrate_mode); > > Beware, that is against the intent of free_folio(). > > Since its 2.6.37 origin in 6072d13c4293 ("Call the filesystem back > whenever a page is removed from the page cache"), freepage() or > free_folio() has intentionally NOT taken a struct address_space *mapping, > because that structure may already be freed by the time free_folio() is > called, if the last folio holding it has now been freed. Thanks for noticing that Hugh, very good point! > > Maybe something has changed since then, or maybe it happens to be safe > just in the context in which you want to use it; but it is against the > principle of free_folio(). (Maybe an rcu_read_lock() could be added > in __remove_mapping() to make it safe nowadays? maybe not welcome.) Let me dig into the callers: 1) filemap_free_folio() filemap_free_folio() looks up the callback through mapping->a_ops->free_folio. Nothing happens in-between that lookup and the callback so we should be good. 2) replace_page_cache_folio() replace_page_cache_folio() similarly looks up the callback through mapping->a_ops->free_folio. We do some operations afterwards, but essentially store the new folio in the page cache and remove the old one. The only caller is fuse_try_move_folio(), and IIUC both folios are locked, preventing concurrent truncation and the mapping going away. 3) __remove_mapping() __remove_mapping() also looks up the callback through mapping->a_ops->free_folio. Before we call free_folio() we remove the folio from the pagecache (__filemap_remove_folio) to then drop locks and call free_folio(). We're only holding the folio lock at that point. So yes I agree, truncate_inode_pages_final() could be racing with __remove_mapping().c That's probably exactly what the docs describe regarding reclaim. rcu_read_lock() should indeed work, or some other mechanism that keeps truncate_inode_pages_final() from succeeding in this racy situation. Alternatively I guess we would have to use another callback. -- Cheers David / dhildenb