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 B7765C54E41 for ; Tue, 5 Mar 2024 22:05:19 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 4145D6B0098; Tue, 5 Mar 2024 17:05:19 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 3C4136B0096; Tue, 5 Mar 2024 17:05:19 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 217726B0098; Tue, 5 Mar 2024 17:05:19 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) by kanga.kvack.org (Postfix) with ESMTP id 0C8086B0095 for ; Tue, 5 Mar 2024 17:05:19 -0500 (EST) Received: from smtpin14.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay05.hostedemail.com (Postfix) with ESMTP id CDFBD401CD for ; Tue, 5 Mar 2024 22:05:18 +0000 (UTC) X-FDA: 81864367116.14.AFEDF34 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by imf14.hostedemail.com (Postfix) with ESMTP id 96362100003 for ; Tue, 5 Mar 2024 22:05:16 +0000 (UTC) Authentication-Results: imf14.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=ZgaZDZ0r; spf=pass (imf14.hostedemail.com: domain of david@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=none) header.from=redhat.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1709676316; 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=DzluRZS8Cm/GFP3w8cOcmLM2pAOUgthF701QClSkUA4=; b=TcLW0Q76Wip0HT+zTd/k/+dOtV3LsXd5q9wXuUN8sNS/iGSKfcAS7Vj9Di+E/OsqVFsJLE 4srjX4DK+pCDgR9MHqWXM6TooVE1UI5Xhkp+gAkkDw1UAkWYilisT+19D+72wi6dlWDHdD 3ZPA6hdX2zwtHH78ZfkoKzc3SDqLHD0= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1709676316; a=rsa-sha256; cv=none; b=obZCWxd5qiaZkGAHuiAzPJKby5M+KJZQ0MN+PKUBmIT4dyGzvCACOK7zobzeWqxnr/wr61 RVoeVhG++lVdz8lEzGnFqRqRuz45MtHDr1fvLRRbJyGRGfWBb0rswq5XIuszXbUdwZ5Jm8 fvUIc8TiTDiw5pzUnePLVkwAWKkFAf0= ARC-Authentication-Results: i=1; imf14.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=ZgaZDZ0r; spf=pass (imf14.hostedemail.com: domain of david@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=none) header.from=redhat.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1709676315; 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=DzluRZS8Cm/GFP3w8cOcmLM2pAOUgthF701QClSkUA4=; b=ZgaZDZ0rZP185/iaXi0Uo2NWfzDaCwekTEuOg8Tzt+QwR6ZzrNBPF/ZHlrEpIFX3HlYqt4 V1nj0RijXsXSvlGw9BQDIKUF0r9EZiRULvI6Ko3guQKXEN6ftQcjwldVi0n8FMIeyJ6hwr L40iThRnchcmH9sBA59zFF0J93G4vvc= Received: from mail-wm1-f71.google.com (mail-wm1-f71.google.com [209.85.128.71]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-600-uLgURKHTN4Se0vvkoNHawA-1; Tue, 05 Mar 2024 17:05:14 -0500 X-MC-Unique: uLgURKHTN4Se0vvkoNHawA-1 Received: by mail-wm1-f71.google.com with SMTP id 5b1f17b1804b1-412f483851fso372145e9.1 for ; Tue, 05 Mar 2024 14:05:14 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1709676313; x=1710281113; h=content-transfer-encoding:in-reply-to:organization:autocrypt:from :references:cc:to:content-language:subject:user-agent:mime-version :date:message-id:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=DzluRZS8Cm/GFP3w8cOcmLM2pAOUgthF701QClSkUA4=; b=ockVpHgkv567ruaZjRAPp8rifoUWB3sV/oMRTTZLJpYEVXHSmD7mKkKeq6zBQ+bkHI 9oJuxI1BXjGXj9dYwYHtYrplU+900qvJWh7mMqhSqp2xyjXyWizRYzXUYjQsjsBzSKAq /5ox62v8AK7BFBNtx/RG6zjSOPSk5ONj8/WknNUucJk8yu+MsVOfdOzTZUbP6GOFPS5e 0SHP2KXo8/pmhmTqzRpkoyo4cnu80zhNthhc/THmpbXzrZ1izlIUfLLX5dNPPEuBDNdS 2DXuvc4g+8SAs/Y3zF7+yO51lzRf+b0EAjFuax+FQyBgKm4zSNhtnfyKtNOjcnEfkQyC RsPQ== X-Gm-Message-State: AOJu0YxNwvAyVywmKQhoZIl5FnF2w7Qhy2c+vKSyt4wei7gsWWVB0y7/ U0W4MhmNSMBnf2/G6nCGQVCOiz59WWuHFCyhByU4+RXhUA1MgZPBX6ikNZzpvZwsXi+Qwp6W114 WBPfXBCif3quqzu7Om6lN1EcXbqPj177uUgaKUcmIvHqRa6pmbRb6TeM7 X-Received: by 2002:a05:600c:1550:b0:412:eef2:f972 with SMTP id f16-20020a05600c155000b00412eef2f972mr1680279wmg.36.1709676313189; Tue, 05 Mar 2024 14:05:13 -0800 (PST) X-Google-Smtp-Source: AGHT+IEccOZTzYunDsM+vNXuQrx4USnVo5MJLdF/Q+aVrijQcyOt2IUcUE3EnE4NNRPsZaaw4tgwTg== X-Received: by 2002:a05:600c:1550:b0:412:eef2:f972 with SMTP id f16-20020a05600c155000b00412eef2f972mr1680267wmg.36.1709676312793; Tue, 05 Mar 2024 14:05:12 -0800 (PST) Received: from ?IPV6:2003:cb:c73c:8100:600:a1e5:da94:a13a? (p200300cbc73c81000600a1e5da94a13a.dip0.t-ipconnect.de. [2003:cb:c73c:8100:600:a1e5:da94:a13a]) by smtp.gmail.com with ESMTPSA id bj1-20020a0560001e0100b0033e48db23bdsm3004511wrb.100.2024.03.05.14.05.11 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 05 Mar 2024 14:05:12 -0800 (PST) Message-ID: <017414bc-78cd-4aa1-9edf-6ce947b9e4e4@redhat.com> Date: Tue, 5 Mar 2024 23:05:11 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1] mm: swap: Fix race between free_swap_and_cache() and swapoff() To: Ryan Roberts , Andrew Morton , "Huang, Ying" Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org References: <20240305151349.3781428-1-ryan.roberts@arm.com> <8989df79-84f5-488c-bd74-c11d2241eff1@arm.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 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: <8989df79-84f5-488c-bd74-c11d2241eff1@arm.com> 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: 7bit X-Rspamd-Queue-Id: 96362100003 X-Rspam-User: X-Stat-Signature: 9qb8owh574afx6p5njztm5use3uo16p5 X-Rspamd-Server: rspam03 X-HE-Tag: 1709676316-244708 X-HE-Meta: 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 t5dANbkg CgRevUfPWeboEjGMBlH8zQcAECCtEpBmIiExnVH7NumPxrfNsJeRL5XJWBZFUPrWc7l4KlODl9IsBMJQSicU/g1ahIGgwnewHMgOiPuhvgfSly4qcBBl2TiygO7OWBJR46exbzsYrrZSF3wlrbZJMLmy1hc55suROSFhQfVgaL+Yg5gBlBqPUwaZY4/flVn7IMSHBGN03CX0Iqbo2ng/oA7VR8g== 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 05.03.24 17:33, Ryan Roberts wrote: > On 05/03/2024 15:50, David Hildenbrand wrote: >> On 05.03.24 16:13, Ryan Roberts wrote: >>> There was previously a theoretical window where swapoff() could run and >>> teardown a swap_info_struct while a call to free_swap_and_cache() was >>> running in another thread. This could cause, amongst other bad >>> possibilities, swap_page_trans_huge_swapped() (called by >>> free_swap_and_cache()) to access the freed memory for swap_map. >>> >>> This is a theoretical problem and I haven't been able to provoke it from >>> a test case. But there has been agreement based on code review that this >>> is possible (see link below). >>> >>> Fix it by using get_swap_device()/put_swap_device(), which will stall >>> swapoff(). There was an extra check in _swap_info_get() to confirm that >>> the swap entry was valid. This wasn't present in get_swap_device() so >>> I've added it. I couldn't find any existing get_swap_device() call sites >>> where this extra check would cause any false alarms. >>> >>> Details of how to provoke one possible issue (thanks to David Hilenbrand >>> for deriving this): >> >> Almost >> >> "s/Hilenbrand/Hildenbrand/" :) > > Ahh sorry... I even explicitly checked it against your name on emails... fat > fingers... No need to be sorry. Even your average German person would get it wrong, because there are other (more common) variants :) [...] >>> >> >> LGTM >> >> Are you planning on sending a doc extension for get_swap_device()? > > I saw your comment: > > We should likely update the documentation of get_swap_device(), that after > decrementing the refcount, the SI might become stale and should not be touched > without a prior get_swap_device(). > > But when I went to make the changes, I saw the documentation already said: > > ...we need to enclose all swap related functions with get_swap_device() and > put_swap_device()... Notice that swapoff ... can still happen before the > percpu_ref_tryget_live() in get_swap_device() or after the percpu_ref_put() in > put_swap_device()... The caller must be prepared for that. > > I thought that already covered it? I'm sure as usual, I've misunderstood your > point. Happy to respin if you have something in mind? No need to respin, we could clarify on top, if we decide it makes sense. I was thinking about something like this, making it clearer that the PTL discussion above does not express the corner case we discovered: diff --git a/mm/swapfile.c b/mm/swapfile.c index 2b3a2d85e350b..646a436581eee 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -1232,6 +1232,11 @@ static unsigned char __swap_entry_free_locked(struct swap_info_struct *p, * with get_swap_device() and put_swap_device(), unless the swap * functions call get/put_swap_device() by themselves. * + * Note that when only holding the PTL, swapoff might succeed immediately + * after freeing a swap entry. Therefore, immediately after + * __swap_entry_free(), the swap info might become stale and should not + * be touched without a prior get_swap_device(). + * * Check whether swap entry is valid in the swap device. If so, * return pointer to swap_info_struct, and keep the swap entry valid * via preventing the swap device from being swapoff, until -- Cheers, David / dhildenb