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=1793091717; b=PP5tpBxWERxKf0JU4jGcmWcr6C3+LKo3p4Yz2S39DJqiOe1ZKhShIjuBdeFRVBK5ZWiT 583n+Nb/ACmM9aFLoeLNzc/XwtnUDTnrbqWI2dm0/BwvhkMeVIbv7jDMUCYcgQ89IekJg kHn0+5hc3nMZFtqz9e3TVqJSI34FJ/NG/Lo0DiaH1MorZ3pMccY1Euz3+r1dvwXD593QG Wcm1lQkVNb268gHk4a0tLHb8YtNO5eZBDJ2TeD0LphTPyMBpeRRNQNJJzPH0IQLDymK95 AFOdA2TTiYBX0/W+/JXSbMXN9dX2JFydZfgYOR3UQUCpCPidFIRWOH+aRptU6iFpCWQ== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793091717; 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=5HfAJvmr7Py4uAnd/ZvUO5cNS3CA+7rdNBTcaC+zq2g=; b=UY4zFD1vmggzwwtg8WXlgx3llKzwk4H5qvWL43ere3jha/J4GjvLFRQ7aReBVh9XNS2J 3W8+K2Apwy2uXLZwLlPeM2MEqmU0hBHyPgGe6QI4ZEbm1w0sGcCJ9bmRwA1C8UU28CrUU R1uYQlRP8iHJDtWwqxpVoc1uroALJ6EwD8RAei/43J2UU2t6HG2Tn0MfXoq8fq5W9Ay6c iBc/uNtl7wvFpDaJnch68YDg26KiXG0s4xP5UPKScWcnZrfhZLMEnsxoepuS743z55rzb 8scuv2jRY6wD0k+YgVCpYtgEmvEUZBYKSdWTxdA/w2+r5Aum2zQuKeEMJ2b6K9K3hDA== 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=bMwTvmpl; 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 08FB2606A31A; Tue, 27 Oct 2026 09:01:56 +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=bMwTvmpl Received: by smtp.kernel.org (Postfix) with ESMTPSA id A377C1F01825; Tue, 27 Oct 2026 09:01:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793091716; bh=5HfAJvmr7Py4uAnd/ZvUO5cNS3CA+7rdNBTcaC+zq2g=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=bMwTvmpl2a3J4HHYmrBE9mt3NWyKTeD3ORLh0ZRiqAeyZcmXKA+47y3CsPp6CRHWt PLhRq3adt2ViR2khWGG5GIfhhxRV3klG739jeG1pjp4CvJNkNV6nChy7vbMnbPQHmP Wogu01k5BoiDB8pqVuvlk3z/Bh2vvuaBDxhWUqR6kY1wpATWson4KGCa2TkiHipc3F zq77uK2T6se4xzGUbtXdL12Z0v7H5+cIAwBv9PFCl/+H+lNBBLf9ZqzjT0/dqRbc7W rraJ7QK+GTgr+FEN2MllkZW0jw0Vr+JlmOahRfiuXhRTJcetNYdOfKEf6L/WpizemW URqTxJVflOI6w== Message-ID: <9620707e-59f3-4b91-87af-2b8e12fed260@kernel.org> Date: Tue, 27 Oct 2026 10:01:48 +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] mm/huge_memory: fix deferred split list corruption on partial unmap To: mt4022@columbia.edu, Andrew Morton , Zi Yan , Baolin Wang , "Liam R. Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Kiryl Shutsemau , Shakeel Butt , Johannes Weiner , "Lorenzo Stoakes (Oracle)" Cc: Kairui Song , linux-mm@kvack.org, linux-kernel@vger.kernel.org, tz2294@columbia.edu, stable@vger.kernel.org References: <20261026-thpsplit-careful-v1-1-d357d70fd6f4@columbia.edu> 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: <20261026-thpsplit-careful-v1-1-d357d70fd6f4@columbia.edu> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 10/27/26 01:22, Mani Tofigh via B4 Relay wrote: > From: Mani Tofigh > > When a THP is partially unmapped while the deferred split shrinker is > scanning it, the deferred split list can end up corrupted. With > CONFIG_DEBUG_LIST, freeing the folio later reports: > > [ 523.871401] list_del corruption. prev->next should be ffd40000005e0090, but was ffd4000000500090. (prev=ffd40000005e0090) > [ 523.871412] WARNING: lib/list_debug.c:62 at __list_del_entry_valid_or_report+0x177/0x220, CPU#0: thpsplit/63 > ... > [ 523.900715] Call Trace: > [ 523.901753] __list_lru_del+0x5f/0x220 > [ 523.902588] __folio_unqueue_deferred_split+0x238/0x520 > ... > > Without CONFIG_DEBUG_LIST, the list is left pointing at the folio > after it has been freed. > > Since commit fafaeceb89a5 ("mm: switch deferred split shrinker to > list_lru"), deferred_split_scan() moves the folios it scans onto a > private list under the list_lru lock, drops the lock, and then removes > each folio from that list with list_del_init(), which sets > entry->next = entry and then entry->prev = entry. Another task may > in the meantime partially unmap the same folio and call > deferred_split_folio(), which queues it only if list_empty() reports > it as not queued, and list_empty() reads only entry->next. If that > happens between the two stores, the folio is queued again, and the > store to entry->prev that follows breaks the new link: > > Task A (shrinker) Task B (partial unmap) > ----------------- ---------------------- > list_del_init(entry) > entry->next = entry > deferred_split_folio() > list_empty(entry) is true > list_add_tail(entry) > entry->prev = entry > /* overwrites the prev link that > list_add_tail() just set */ > > Use list_del_init_careful() instead. It sets entry->prev first and > then entry->next with smp_store_release(), so once list_empty() sees > the entry as empty, the shrinker has finished writing to it. > > The reproducer repeatedly faults in THPs and partially unmaps them > while the deferred split shrinker, run through > /proc/sys/vm/drop_caches on the same CPU, is scanning them. This bug > was found and replayed using a deterministic hypervisor currently > under development, but the non-deterministic C reproducer can > typically trigger it in the 10-500s time range. With the fix, nothing > is triggered after 1800 seconds. > > Fixes: fafaeceb89a5 ("mm: switch deferred split shrinker to list_lru") > Cc: stable@vger.kernel.org > Signed-off-by: Mani Tofigh Are we now sending alterantive fixes for anything already posted? :) https://lore.kernel.org/r/20261027-fixes_core-v1-10-6f74bec9a5bb@kernel.org If there is a better way to handle it reply to fixes already posted. -- Cheers, David