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a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1781246881; b=uS63XEk2/yYA2yhTwZmoDOAcBb0J7oKyFbOLpte0vhjtW4Y6ixqsFiT58zELGu8TfGlgS1 cQRNygJi3WC+jN30BrnytPTNfBSxFKPYd0qiTOL9v7LN0wf5cfsTPOfyynINRatvwtv9Jw wQEB0wlTndZZHbjn6jkSSkckARcSRl0= ARC-Authentication-Results: i=1; imf03.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=ZYA1nWDv; spf=pass (imf03.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id F1C4C6001D; Fri, 12 Jun 2026 06:48:00 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 797EA1F000E9; Fri, 12 Jun 2026 06:47:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1781246880; bh=PYKn3nqZTI2tONzA/mOunAmSCw2g+cgo26Rk9W8RKAY=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=ZYA1nWDv5Kwx1F24wjee8yzwFfyzxfMG+g8cWzvDB3bEUM+EMfkYHp6ABVQ9fRMRd T5YaKhfOZpYQjxQU55MBSKLYilBqhXMvNrhHHGQz0r5o04LvFzqj1rNcrziQdVjqP5 mgtT8FWQIY1P31vj/uykTfWkQu0gBpfZw99wjX6jGNrUV2PDEYvnBtoqU3CySIrALy c0uK5vi5VyyvoR4M61Fey8iKtYLRqwIN9V4ezzbThVuHfPlSWKV9B5KcQUd5VfJtEf LhU0zo6Whc6grmxDSJ4nryzfJ1hJZmrVx0NeoenuHrCQEF05auuoCz8/cxxtl4d03M Q5Rw7oS+Las7Q== Message-ID: <884cf1df-2256-4eb9-a2cb-67377a3bd8f6@kernel.org> Date: Fri, 12 Jun 2026 08:47:55 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/gup_test: fix race with PIN_LONGTERM_TEST ioctls To: John Hubbard , Yunhui Cui , akpm@linux-foundation.org, jgg@ziepe.ca, peterx@redhat.com, yang.lee@linux.alibaba.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: stable@vger.kernel.org References: <20260608025043.88087-1-cuiyunhui@bytedance.com> <932e1fa0-dd9e-47d2-9133-d3b2f78dcd97@nvidia.com> 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: <932e1fa0-dd9e-47d2-9133-d3b2f78dcd97@nvidia.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 752AD20004 X-Rspam-User: X-Stat-Signature: 17jbxfumknfxbwzzrnndef5zreatrn1x X-Rspamd-Server: rspam08 X-HE-Tag: 1781246881-937973 X-HE-Meta: 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 IojMKZRf TN6oFmecXtH3GNQw6w8kLKmC0+Wri1cBKKUGBFV4BSwWSwAJ1P0ypJuMMBQkp0A8Dju/0x2fHT1fe1z1PboD5+4WaaUuPWZYgTktJHaU++zzcy5CEzGDN2b9n+fcC3LYH7rxdCRBNSQv15/0i6QFgIzKwp9yp06BWvAr/HNwZS/WlVnei2iFkJ9l/4j24Gv8aJtFAubO0Z5jSglVKb31jvUXkpNotcoxsS/wQbBJIMvGCAQ3kt74rw6hI5LkKCIeqX+LCH9GQk6IVR/XvaRZOKtrgvpetP+GOUi4bUYiB7SXw5nyJ8EhZcTl1PQZUpxwK48TwKTPIwFf3Yms= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 6/12/26 06:20, John Hubbard wrote: > On 6/7/26 7:50 PM, Yunhui Cui wrote: >> The PIN_LONGTERM_TEST helpers keep their state in global variables that >> are protected by pin_longterm_test_mutex when accessed from ioctl(). >> However, gup_test_release() calls pin_longterm_test_stop() without >> holding that mutex. >> >> This can race with PIN_LONGTERM_TEST_STOP and let two callers operate on >> the same pages array concurrently, corrupting the test state and possibly >> freeing it twice: > > Let's add here that there are *no* such callers in the kernel, today. > >> >> CPU 0 CPU 1 >> ----- ----- >> ioctl(PIN_LONGTERM_TEST_STOP) >> mutex_lock(&pin_longterm_test_mutex) >> pin_longterm_test_stop() >> if (pin_longterm_test_pages) >> kvfree(pin_longterm_test_pages) >> >> close() >> gup_test_release() >> pin_longterm_test_stop() >> if (pin_longterm_test_pages) >> kvfree(pin_longterm_test_pages) >> >> pin_longterm_test_pages = NULL >> mutex_unlock(&pin_longterm_test_mutex) >> >> Protect the release path with the same mutex so that stop and release >> cannot run pin_longterm_test_stop() concurrently. >> >> Fixes: c77369b437f9 ("mm/gup_test: start/stop/read functionality for PIN LONGTERM test") >> Cc: stable@vger.kernel.org > > umm, no, to "Cc: stable". This is the sort of thing that gives AI > a bad name. Specifically: > > * Nothing in tree can possibly hit this race condition. > > * This fix is purely static code analysis hygiene: correcting > a theoretical problem that does not actually provide any > sort of vulnerability fix in the kernel. > Yes, all rather useless churn that consumes our capacity. -- Cheers, David