From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 12D5FCAC5B0 for ; Thu, 2 Oct 2025 11:39:09 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 5BD208E0008; Thu, 2 Oct 2025 07:39:09 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 56D068E0002; Thu, 2 Oct 2025 07:39:09 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 434EC8E0008; Thu, 2 Oct 2025 07:39:09 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0014.hostedemail.com [216.40.44.14]) by kanga.kvack.org (Postfix) with ESMTP id 2CB838E0002 for ; Thu, 2 Oct 2025 07:39:09 -0400 (EDT) Received: from smtpin15.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay06.hostedemail.com (Postfix) with ESMTP id CD50311A0DB for ; Thu, 2 Oct 2025 11:39:08 +0000 (UTC) X-FDA: 83952977976.15.AB08E4F Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by imf28.hostedemail.com (Postfix) with ESMTP id 70381C0002 for ; Thu, 2 Oct 2025 11:39:06 +0000 (UTC) Authentication-Results: imf28.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=HyOBtIWb; spf=pass (imf28.hostedemail.com: domain of david@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=quarantine) header.from=redhat.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1759405146; h=from:from:sender: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:dkim-signature; bh=Qa8gIa0V21yaVB+/eCXge80xz63JZQgqa74/kUyfFBg=; b=Zip/Hjg8b8OregSnmae+rr8Rfw4ztH4fBTQrN78/mUqJtEsf5fCL8aJoOR0JQHfi3xyqxT NSFWU2Sk8kvE7pqtAl2geEGZy2SSCYsGRj8kFo2/aR25KsWkGjkcJFvnqSHduHt8E/0J2p eTG2iaPFH5mhE50yKBfU6OpqfxPQoCw= ARC-Authentication-Results: i=1; imf28.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=HyOBtIWb; spf=pass (imf28.hostedemail.com: domain of david@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=quarantine) header.from=redhat.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1759405146; a=rsa-sha256; cv=none; b=IePODxJcsSDu+DXD/onkp09wzQUrPRp5SY3JM6v+s2iAQLr61+lxbsdOvbPmRSzD7sGEha P5wdLvzGDbTMnBrNiWvGHmeiPgZ5PMTpC7kkGtVylinkS0/4vW0t8A0M+svauc96YqwW4K QHDT/hTuiKsxf6W+n4mnHltO61bwqkM= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1759405145; 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=Qa8gIa0V21yaVB+/eCXge80xz63JZQgqa74/kUyfFBg=; b=HyOBtIWblvEJEBXvN6GOv0umpXcHxwQEIoGzcslRPqiw46gCXoLZZjyvoBYMbJY8FwFPCs mDh511PF+GsG6ezaRTztqcNEttZwNfn1TVSDz1n61i1oDH2zeI0RGTu3LaYGmuCsVUIMIS /MnMz7kSRIzYfXjgWMFRfEkLsmPezbo= Received: from mail-wm1-f72.google.com (mail-wm1-f72.google.com [209.85.128.72]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-393-DhO7xu8fO2aj-rE8lLn2Cw-1; Thu, 02 Oct 2025 07:39:04 -0400 X-MC-Unique: DhO7xu8fO2aj-rE8lLn2Cw-1 X-Mimecast-MFC-AGG-ID: DhO7xu8fO2aj-rE8lLn2Cw_1759405143 Received: by mail-wm1-f72.google.com with SMTP id 5b1f17b1804b1-46e377d8c80so3030885e9.3 for ; Thu, 02 Oct 2025 04:39:04 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1759405143; x=1760009943; 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=Qa8gIa0V21yaVB+/eCXge80xz63JZQgqa74/kUyfFBg=; b=eW0WaUZyhEUAt3fK9PtNqngejM/CaneytO2a2AU/6IPznGsDnyct5lDIqz87LNxCuA 5Q0JuzyPO599qLrQUe9WURQlfRGIcIJicpcewDfi1uQWZupNLo/Znuvjw/gKrFz5ZMV2 f5jP68ipfoVMfgGujnEV/8Zdj3rjloZmhe4Cue8JcA8nelv68gTKAVE5rulX4cBYpNut G5EcJH+HoEijPPYy7+DkUC89aAnjpEcw6SddG96jqAurvizMFoRo8fqWAps2OoWiCpEw rFN7W1uxJkt2ywlTC72riYmDDa+CufpPul/UasVq8oXRIPxZtMV4K4+UWDJ88f6N2nng j7pQ== X-Forwarded-Encrypted: i=1; AJvYcCXsfDtPH8+lEGnNYC7fua52NQ58BjGlwC2lgkOAJ2jlVgdm+KZpxOzyy1NGCJhhH8enMRKw1n3OFw==@kvack.org X-Gm-Message-State: AOJu0YwMNAh3ePMCKAH59tC6A+L4Bg/uVkOtk0DonZGKZztSHPz7PgEL yp62fZAY61BYoerEBQzg/WLd3lL8I22zDa0eEp3hypYxUOSHa1ixdOtVyZXh6xOUcSGggtU8pLm bGyj7F4UHbUorKRnoq725hUx1a5Y0uYWaN+2JfLdhNf/R9Eu1AEmW X-Gm-Gg: ASbGncshC9Y9ak8AlTWjWxh5LTXcPC53twoOuLT+AYi2SARRBnk+SG7JA7Pa1fZRQzo RRMSSZrG1+5BVrosjw8qhhd71MNQVdZwzhT8eXrNGPmT1RKeNDD1JNvJJCnL4bH+duTY2YkUEEG CPVH12uezq1xH60PQabi4hkG+GKEBYjBiNbOWCZk1QxjqJqyrgngv1I5AQilsuPwDSRGA+Yi70G TLjR8rCwQg4oMtB5fFTBqOHWOjHHp2P/aP4Q8VfnjWjg3LNdkaaSG2ISXMaFyqGzlS/X5iCvI5K EXYWj/p+kh0krb4KnWrjAEx8TOoleiBgmfqUXVX3QDd0bErwJk/Q7DB6zsE5riq//QmDWEiYxNS uRjGBpbea X-Received: by 2002:a05:600c:3e10:b0:46e:5aca:3d26 with SMTP id 5b1f17b1804b1-46e653f84camr38704705e9.22.1759405143345; Thu, 02 Oct 2025 04:39:03 -0700 (PDT) X-Google-Smtp-Source: AGHT+IEyThTO2nCYVKvGrKXsprfkdDNwOhJqAGfAyefFwycoBiTM+WyfaA8y0YZWBdbXDJvOp6TQbQ== X-Received: by 2002:a05:600c:3e10:b0:46e:5aca:3d26 with SMTP id 5b1f17b1804b1-46e653f84camr38704395e9.22.1759405142936; Thu, 02 Oct 2025 04:39:02 -0700 (PDT) Received: from [192.168.3.141] (tmo-080-144.customers.d1-online.com. [80.187.80.144]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-46e5b69bc0bsm54311425e9.3.2025.10.02.04.39.00 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 02 Oct 2025 04:39:02 -0700 (PDT) Message-ID: <9a586b5b-c47f-45eb-83c8-1e86431fc83d@redhat.com> Date: Thu, 2 Oct 2025 13:38:59 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC] mm/migrate: make sure folio_unlock() before folio_wait_writeback() To: Byungchul Park , akpm@linux-foundation.org Cc: ziy@nvidia.com, matthew.brost@intel.com, joshua.hahnjy@gmail.com, rakie.kim@sk.com, gourry@gourry.net, ying.huang@linux.alibaba.com, apopple@nvidia.com, clameter@sgi.com, kravetz@us.ibm.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, max.byungchul.park@gmail.com, kernel_team@skhynix.com, harry.yoo@oracle.com, gwan-gyeong.mun@intel.com, yeoreum.yun@arm.com, syzkaller@googlegroups.com, ysk@kzalloc.com, Matthew Wilcox References: <20251002081612.53281-1-byungchul@sk.com> From: David Hildenbrand 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: <20251002081612.53281-1-byungchul@sk.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: aIN9dC05J8TMW1heWUuxVzxtSWWbc6f9kpMF1ssyWj4_1759405143 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 70381C0002 X-Stat-Signature: qnoxiobbc554htrkzrbrj7h43tzmhzn8 X-HE-Tag: 1759405146-4281 X-HE-Meta: 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 0ZMjtL69 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: > To simplify the scenario: > Just curious, where is the __folio_start_writeback() to complete the picture? > context X (wq worker) context Y (process context) > > migrate_pages_batch() > ext4_end_io_end() ... > ... migrate_folio_unmap() > ext4_get_inode_loc() ... > ... folio_lock() // hold the folio lock > bdev_getblk() ... > ... folio_wait_writeback() // wait forever > __find_get_block_slow() > ... ... > folio_lock() // wait forever > folio_unlock() migrate_folio_undo_src() > ... > ... folio_unlock() // never reachable > ext4_finish_bio() > ... > folio_end_writeback() // never reachable > But aren't you implying that it should from this point on be disallowed to call folio_wait_writeback() with the folio lock held? That sounds ... a bit wrong. Note that it is currently explicitly allowed: folio_wait_writeback() documents "If the folio is not locked, writeback may start again after writeback has finished.". So there is no way to prevent writeback from immediately starting again. In particular, wouldn't we have to fixup other callsites to make this consistent and then VM_WARN_ON_ONCE() assert that in folio_wait_writeback()? Of course, as we've never seen this deadlock before in practice, I do wonder if something else prevents it? If it's a real issue, I wonder if a trylock on the writeback path could be an option. -- Cheers David / dhildenb