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=1793114168; b=M+31VfqWXGZg5CnzKA28esLeFvwfSSkE6PUXxiHTSmH+ufCA+t8ZFV/B8AnCQFV/2xJh 3H0n+cqsFgugh6OUL0RTKiglS/JWMyXfumR+XLuCNAjRCf4VSyiWW6n0pUQ+qgn2ZLf9t We02Z7YI9+IwduhPb0ZzFHxiFiVz3/wFVTg6aCEEg7V2c00eDAGDSRI+ST6SAx9uvxNEe ba7BwSMoHKAWzTfUJbN/T0x5VW1xogRRV3Yu7/tBMboqHLBcQRco8WG/CqmTToPbFayzf SzCna/mdJoDGvPiyjWSkarDtB8e66/QX3CEzKEqEDHz8l4CMMJZla65yhgHmwouIjYg== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793114168; 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=WyoOBEMd5hZXCT3U6GbGErLU5iMuF52Y0APEdOL8vu8=; b=LuHII0Yn+58D2zWAC89wiU0zMHuMkrbWxJJIlftTS322CZMpcR189EMHucgLCIGrHNLI /2QwrYSoYquK0MkKtK952oxcWVojDRcI1Z7BvAAk/yUKCaC63hVXLrffaIxz6qHhC6Nhf tPXvsPtNLx4bjt5ppksvMV7fHQf/f37YU3t7rlPe0j4IKBRvidSekM9JswE4XXBJuL8Uv ESTXN2uYAjha2x3PalM84c5JYkDw/ePn5P90081qF86pzMSLNQf+dW9F37qY6l28cPlUf Sr7n11WkOgFu5A2/1XdXc64EZvS2pR2e26yNxayzbpPkf/7gvfZ+fUsrLpB2ITFH55w== 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=BuxeSr53; 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 A99D6606A31A; Tue, 27 Oct 2026 15:16:07 +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=BuxeSr53 Received: by smtp.kernel.org (Postfix) with ESMTPSA id B7B361F031E1; Tue, 27 Oct 2026 15:15:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793114167; bh=WyoOBEMd5hZXCT3U6GbGErLU5iMuF52Y0APEdOL8vu8=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=BuxeSr53N6HezVPXpkTBwQAyxXiQXQMGirT/jWdAIMpopdRAYo1tvjPz9Mj4TZHOA kCKNMi0nV3dg0g3jZfLVdgzt3vZSG9lLq4AlcR0a+e3VBnedC3bymzXL9oG1SO4iWE fJACOUUU87ggc+1eu6u1/KKjtn7CLcF6A2wbcLzhoj+dB1tLXLa4KYbKieq7i748iY o2gmuzLNkgoyi0AYn+LoxhMR9H3ei2rAbSx/PGsiegdwDvsYnH1pr2f40NOC0DMtB9 f87YgVhTqm0YPh9Nk+7DlZiCPK/LFgzZC/NqNbunFZp6vNHVfwUP/noI2x1kVbeQS1 xgersgMKHm9Ew== Message-ID: <5d431bf7-8813-4e2c-a40d-b45d4ff39a5b@kernel.org> Date: Tue, 27 Oct 2026 16:15:48 +0100 X-Mailing-List: linux-arch@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 10/46] mm/huge_memory: fix list corruption when deferred_split_scan() races with deferred_split_folio() To: Johannes Weiner Cc: Andrew Morton , Michal Hocko , Qi Zheng , Shakeel Butt , Lorenzo Stoakes , Kairui Song , Barry 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 , Pedro Falcato , 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-v1-10-6f74bec9a5bb@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: 7bit On 10/27/26 15:10, Johannes Weiner wrote: > On Tue, Oct 27, 2026 at 12:17:30AM +0100, David Hildenbrand (Arm) wrote: >> Since the deferred split queue became a list_lru, the isolate callback >> moves the folios it took a reference on to an on-stack list, linked >> through folio->_deferred_list, and deferred_split_scan() takes them off >> that list with list_del_init() without holding the list_lru lock. >> >> deferred_split_folio() does not know about the on-stack list. It only >> holds the list_lru lock when it looks at the same list_head, and it can >> run for such a folio: a THP is queued when it is mapped, as a candidate >> for the underused check, and is queued "again" when a part of it gets >> unmapped: >> >> CPU0 deferred_split_scan() CPU1 deferred_split_folio() >> list_del_init(&folio->_deferred_list) >> next->prev = prev >> prev->next = next >> entry->next = entry >> list_lru_lock_irqsave() >> folio_set_partially_mapped() >> __list_lru_add() >> list_empty(item) -> true >> list_add_tail(item, &l->list) >> item->next = &l->list >> item->prev = tail >> entry->prev = entry >> >> The folio now sits on the list_lru with ->prev pointing to itself. The >> next removal leaves the neighbours pointing to it, and they still do so >> after the folio has been freed. With CONFIG_DEBUG_LIST: >> >> list_del corruption. prev->next should be ffd4000000270090, but was >> ffd4000000278090. (prev=ffd4000000270090) >> >> Fix it by grabbing the lock around list_del_init() so >> deferred_split_folio() cannot race with it. >> >> Fixes: fafaeceb89a5 ("mm: switch deferred split shrinker to list_lru") >> Cc: stable@vger.kernel.org >> Reported-by: Josef Bacik >> Signed-off-by: David Hildenbrand (Arm) > > Reviewed-by: Johannes Weiner While I have your attention: This variant works, a different proposal used list_del_init_careful() instead. However, that is documented to require list_empty_careful(). Do you think it's worth looking into? https://lore.kernel.org/all/20261026-thpsplit-careful-v1-1-d357d70fd6f4@columbia.edu/ -- Cheers, David