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]) by smtp.lore.kernel.org (Postfix) with ESMTP id D791FC54791 for ; Wed, 13 Mar 2024 09:20:54 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 6B7B180016; Wed, 13 Mar 2024 05:20:54 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 63FF2940010; Wed, 13 Mar 2024 05:20:54 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 4929180016; Wed, 13 Mar 2024 05:20:54 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0012.hostedemail.com [216.40.44.12]) by kanga.kvack.org (Postfix) with ESMTP id 3415F940010 for ; Wed, 13 Mar 2024 05:20:54 -0400 (EDT) Received: from smtpin20.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay10.hostedemail.com (Postfix) with ESMTP id 04DC0C05E4 for ; Wed, 13 Mar 2024 09:20:53 +0000 (UTC) X-FDA: 81891471228.20.AF96A5E Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by imf13.hostedemail.com (Postfix) with ESMTP id E503420011 for ; Wed, 13 Mar 2024 09:20:51 +0000 (UTC) Authentication-Results: imf13.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=a8vGs0dm; dmarc=pass (policy=none) header.from=redhat.com; spf=pass (imf13.hostedemail.com: domain of david@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=david@redhat.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1710321652; 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=c2M3LKMI7QfczGcDJAGI5KsDzIjqnnTlLNKwFzjNrpY=; b=5CO5a/pwW4opLjeUk6n4ZgKFa400yG5AtdZzqACDgKHkxEzOPaJrbugoJag/bGptWqpoYn 2qQFmAhbqN0RERcSpfZxtvf2rXXZIHiBtCzVARni8ZgYWEbwCXu/QeULnJCbuaKfUdIaOM E20xgptiJb5If2Tf9QFe9THmgqtc2Gw= ARC-Authentication-Results: i=1; imf13.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=a8vGs0dm; dmarc=pass (policy=none) header.from=redhat.com; spf=pass (imf13.hostedemail.com: domain of david@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=david@redhat.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1710321652; a=rsa-sha256; cv=none; b=o0Uvuk9kxzTyTIizwxNHUow8297/W6jf49hibs66FDUWmZuE4KJPFNEMth5Hb1FO3oxKJZ hFF0yPqvHJA4nDkegtz99HVhtaYNaAORGXuzuLDGIvkuuwboNRDGcLAuXaq9bpqTZI/TDU Atd0w5ROZQfzRMtwqL3xnmK1gLGIM5I= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1710321651; 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=c2M3LKMI7QfczGcDJAGI5KsDzIjqnnTlLNKwFzjNrpY=; b=a8vGs0dmaFsdiy1aD9UwdPmGt9KJc0SFU5LxP90ccnhozsk99w3tQ3FVPF6gOL4KJr4qUp aDLaByqrwUSk5RfAkj2TN24FgDa3gTIMcNmhBkGLm9P2pMHnoYAi/YtlAnqafL/zdePwNv Kn8E40PSPQejVACx8gfEnrpcAXna510= Received: from mail-wm1-f69.google.com (mail-wm1-f69.google.com [209.85.128.69]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-447-oNUpCjEmN5uzeGLdzYsNqg-1; Wed, 13 Mar 2024 05:20:49 -0400 X-MC-Unique: oNUpCjEmN5uzeGLdzYsNqg-1 Received: by mail-wm1-f69.google.com with SMTP id 5b1f17b1804b1-41312565bd4so4140965e9.2 for ; Wed, 13 Mar 2024 02:20:49 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1710321648; x=1710926448; h=content-transfer-encoding:in-reply-to:organization:autocrypt:from :content-language: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=c2M3LKMI7QfczGcDJAGI5KsDzIjqnnTlLNKwFzjNrpY=; b=oH9cE3cqzFAmi6QYDDMEPHIBwyiVShI28yhw5qHHK+S/psZfHx6lY8tyUEEm/jJEMu y4od2iKy9KejcywtJJ2u40FCMrcDBZn9K3fItc+O14e6yQXqTUQ/u29Mtyg2vBNK5WUm mNuUENJTyE7dsTNlAFxNL4i0BgVVrHw8avnzPdKxszgOkTyT4p5OIRgbouszfCsgjSH1 xPUxPKT5nAw0lyyuNw+SnPY/XDg9GlM7E7BFk3v4nVDO2vL6S+cOsskWWm4FIKutQxlJ lmif+zO6Arh7ySH8r/6gkUWzOBgDFszWlsOWgZOYDVzAjCRk4r3/aPwD8lryxOpVEir0 BJIw== X-Gm-Message-State: AOJu0YxPQyhjshdiMO+TyNtflI9FmKgM5fW3TZ7sKOLQmzxNhtxsAWl/ 7f04j88ZSmGkIscczt0xt56iaZMUodPKSfvAvL1owOI4e0vr01+JDOmOM1/ZBfDYq4LXHFUJGGa OLcaOcLJfLPhsxLiWWHfunZ3T3CIflYwwIKQeCz6GcxDy7F1j X-Received: by 2002:a05:600c:a001:b0:413:e84a:572d with SMTP id jg1-20020a05600ca00100b00413e84a572dmr1339746wmb.37.1710321648405; Wed, 13 Mar 2024 02:20:48 -0700 (PDT) X-Google-Smtp-Source: AGHT+IEZm1mRTk8AvXgGjP6KC+YKPpioKiqrg4rw2omoVMNGzZ3FYd05bag/ReG09aVPDCk1Dq4DYg== X-Received: by 2002:a05:600c:a001:b0:413:e84a:572d with SMTP id jg1-20020a05600ca00100b00413e84a572dmr1339729wmb.37.1710321647954; Wed, 13 Mar 2024 02:20:47 -0700 (PDT) Received: from [10.32.64.142] (nat-pool-muc-t.redhat.com. [149.14.88.26]) by smtp.gmail.com with ESMTPSA id d3-20020a05600c34c300b00413eac2e806sm1082049wmq.29.2024.03.13.02.20.47 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 13 Mar 2024 02:20:47 -0700 (PDT) Message-ID: <57c9e228-9aca-4da6-a714-f175f053ff50@redhat.com> Date: Wed, 13 Mar 2024 10:20:46 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: Splitting pinned folios To: Matthew Wilcox , Jane Chu Cc: linux-mm@kvack.org, John Hubbard References: 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 ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: E503420011 X-Stat-Signature: wxn3fykbuwkfw597bhozwseanybhuroy X-Rspam-User: X-HE-Tag: 1710321651-462482 X-HE-Meta: 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 M61xNay2 2wqA7L8sd3EhEbMGFmh9GaE2+iX+vP1jv/LHdK6Lcv+UqzElM+JBkqs6mOaNE3K1gZ4o67iRs9gtBbkRMfVPMsRUz02SLJvptzHBrKIT/gvj6cmxqLijUTeYZ6ph7vKpKUz3GN8cbCKseCdxsWbBbJxAW9SdvE5K2t++Z 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: On 13.03.24 04:16, Matthew Wilcox wrote: > On Tue, Mar 12, 2024 at 06:23:43PM -0700, Jane Chu wrote: >> I noticed this recently > > OK, this is entirely different, so I'm going to start a new thread ;-) > >>  * GUP pin and PG_locked transferred to @page. Rest subpages can be freed if >>  * they are not mapped. >>  * >>  * Returns 0 if the hugepage is split successfully. >>  * Returns -EBUSY if the page is pinned or if anon_vma disappeared from under >>  * us. >>  */ >> int split_huge_page_to_list(struct page *page, struct list_head *list) >> { >> >> I have a test case with poisoned shmem THP page that was mlocked and >> >> GUP pinned (FOLL_LONGTERM|FOLL_WRITE), but the split succeeded. > > I'm going to blame John for this! The description is wrong. Whoever calls split_huge_page_to_list() must hold a folio reference. That folio reference will be transferred to @page (not the head page) once split. So @page can be used by the caller after the split succeeded. > There's no reference to pincount > anywhere in huge_memory.c, so I have no clue how this comment is even Each pincount increment/decrement must be paired with a folio refcount increment. Therefore, no pincount checks are required. > close to true, nor do I understand how it could be done, since we don't > know which pages in a folio are pinned. As the description correctly says: "Returns -EBUSY if the page is pinned". If that is not true, we'd have a real issue. > > I think we have to prohibit splits of folios that are GUP pinned. > In split_huge_page_to_list(), we make sure there are no additional folio references of any kind (GUP pin, whatsoever). can_split_folio() is racy but catches most of that. Then, we do the folio_ref_freeze(). So I don't see how that could ever work with additional folio references (including GUP pins). Unless serious BUG somewhere else. In essence: we expect on a folio after completely unmapping it: * 1 reference from the caller of split_huge_page_to_list() * pagecache: 1 reference per subpage from the pagecache * anon: 1 reference per subage from the swapcache if in the swapcache Any additional reference would lead to a split failure. We're holding the folio lock, so for anon folios we cannot remove it from the swapcache concurrently. For pagecache folios ... dunno :) I expect some folio-lock magic as well. Reading "I have a test case with poisoned shmem THP page that was mlocked and GUP pinned (FOLL_LONGTERM|FOLL_WRITE), but the split succeeded." If that is indeed true, I assume that page poisoning might have done something very wrong with the large folio: for example, partially unmap it from the pagecache (if that's even possible?) or accidentally drop a folio reference. Then, we'd be missing to detecting the GUP pin when freezing the refcount. ... any chance we can get the reproducer? [reading this mail from Willy only] -- Cheers, David / dhildenb