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=1793271484; b=4AKQl1ZhSD8AMLwhpiEYTAYKZiYYNJOJnFN3BVtPRSbCFnO2wwylR7utilct6Hkc9PYF AiJMbpOgu7Efh7bw2nq9Zfbt3+SxTHB5fc8pUF5b0MgmmyAb1ryMWkuZ+9iIrZoSuIf/T vCiZ42hHdMkTWR/Iat+WuMdf3nYQbHm5crSequEpknv+7uKAGyYJPyJsyKH9OauR0ZOZk 0BC71mbpWed4VuVDyOAc/TleoB4JS+j3KutwXV9qVq8tNer1iv01uM8h5EJXhbcuEMQ/q d+1d6m5gVAfsQDDQ+D+jvg6P2ZoqpBryw3exYkBEbi+TT7k+w0wdRqYtZGz7jJ90dQw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793271484; 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=HRlYvtp0NLbF/qBaWCj/ZYIcUA7W6S9v5stNA3ILEuU=; b=hqJW1VxKyFuQKY4PAxInhr9RP4Rr56ZrJrPFitMQBTDes/acvtl1wHGjPoW9XG9N1Tnx yxPzI/Mqm0HR5whzhrEzcQl0LgT0qTR8z6Jn/NqBUe/V/s5u9vf38m0ucTd1CpCkRQNvH h6bfQsgFLnS3bbXS/ktYKfS8YIL+5iEg+LzTf9ts2UVqV1VudIeVK/C+47xYfAmxkS0ms eJlwJtn5J/70Pv3o3FEioLLaZGszrwk5ZMrAc9mWes09pCzbNxcNvY1ehBcEjBJM5EzFl ETDk7FOPExSl0PKo9CF5MJ7VmuR7/Bl+d1doLTkW+TuRM4a2n23UCRIFWLOP1TWhkjw== 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=H3FsUol2; 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 3F8EC606A31D; Thu, 29 Oct 2026 10:58:04 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=H3FsUol2 Received: by smtp.kernel.org (Postfix) with ESMTPSA id F11AA1F01825; Thu, 29 Oct 2026 10:57:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793271483; bh=HRlYvtp0NLbF/qBaWCj/ZYIcUA7W6S9v5stNA3ILEuU=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=H3FsUol2krhWc0MOsqYSy4b1n5I/yEBuYGJf4ssu48mgFUkvW+0qm9DYEj2+lgKgm fFIbgCvBARf3WoqRQM+NLSRyK4kJJtyXKF974wXPAnGy4mgrBPrkqSLraPFBxk9NfV L82qn5kVuNTWaxKH3veWkSXybe31FXgnFOznG6WMGFZe9paGUxsFhSbjUdaJI80DAR 97c4aNlaizxp0hL3Aeed13cW6uSdzU+3T6iuag663YJN6movTiPMGWocBnKF741/kS kb2KEPH80ay4scp18cnaw4P1KMwb8sIEcjlJBYfiyGroVIGDg6lz21BKMsUllLAqh1 0vJP7Pj5AIqZA== Message-ID: Date: Thu, 29 Oct 2026 11:57:42 +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: [PATCH 02/46] fork: take mmap_lock before copying mm_struct To: Barry Song , Pedro Falcato Cc: Andrew Morton , Johannes Weiner , Michal Hocko , Qi Zheng , Shakeel Butt , Lorenzo Stoakes , Kairui Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , Baoquan He , Baolin Wang , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Kees Cook , Peter Zijlstra , Jann Horn , Hugh Dickins , Pasha Tatashin , Pratyush Yadav , "Matthew Wilcox (Oracle)" , Jan Kara , Zi Yan , Lance Yang , Rik van Riel , Harry Yoo , Alistair Popple , Nico Pache , Ryan Roberts , Dev Jain , Usama Arif , Kiryl Shutsemau , Matthew Brost , John Hubbard , Peter Xu , Will Deacon , "Aneesh Kumar K.V" , Nick Piggin , Oscar Salvador , Minchan Kim , Muchun Song , Xu Xin , Chengming Zhou , Chris Li , Kemeng Shi , Nhat Pham , Youngjun Park , Gregory Price , Joshua Hahn , Rakie Kim , Ying Huang , Jason Gunthorpe , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kexec@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org, linux-cxl@vger.kernel.org, stable@vger.kernel.org, Josef Bacik References: <20261027-fixes_core-v1-0-6f74bec9a5bb@kernel.org> <20261027-fixes_core-v1-2-6f74bec9a5bb@kernel.org> <22b819a2-631d-468e-b724-770caf9f94e4@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: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 10/28/26 22:11, Barry Song wrote: > On Wed, Oct 28, 2026 at 8:55 PM Pedro Falcato wrote: >> >> On Wed, Oct 28, 2026 at 03:48:09AM +0800, Barry Song wrote: >>> On Wed, Oct 28, 2026 at 3:07 AM David Hildenbrand (Arm) >>> wrote: >>> >>> Regarding the race with memcpy(mm, oldmm, sizeof(*mm)), we >>> still have one [1] even after this patch. >>> >>> That is, copying mm_struct can happen concurrently with >>> lru_gen_del_mm(). However, this race doesn't seem harmful. >>> I might be missing something here though. >> >> I don't think it's harmful as well. mm_init() reinitializes those fields. >> >> Though I hate that memcpy. I think that ideally we copy by member and >> data_race() benign races, like what is done in vm_area_init_from(). > > Yes. I was suggesting something like using data_race() to > silence the warning[1], but applying it to memcpy() also > seems a bit too drastic. > > Another option is to copy members one by one, skipping those > that don't need to be copied. However, that would make the > code quite lengthy, and the copying might also be slower? The compiler might do its best to improve it, but I don't think this is the direction we want. We'd have to figure out > >> >> Anyway, KCSAN reports aren't the most serious thing in the world, so this can >> (should?) be cleaned up later. > > Yep, I don't think there are any blockers for this patch. I had > actually given my Reviewed-by tag before raising this race. > > David discussed races between memcpy() of mm_struct > and other operations. I recalled another related case, so I > posted it here. Hopefully, I'm not just making noise. Not at all. I think that needs a proper investigation as well ... and I am still u clear how it would be valid to access the mm struct without the mmap lock (per my patch) that way. -- Cheers, David