From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 9CBDA606A32E for ; Tue, 27 Oct 2026 15:16:13 +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 kanga.kvack.org (Postfix) id 95E906B07BE; Tue, 27 Oct 2026 11:16:12 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 910286B07BF; Tue, 27 Oct 2026 11:16:12 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 7FED76B07C0; Tue, 27 Oct 2026 11:16:12 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0017.hostedemail.com [216.40.44.17]) by kanga.kvack.org (Postfix) with ESMTP id 5860B6B07BE for ; Tue, 27 Oct 2026 11:16:12 -0400 (EDT) Received: from smtpin21.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay01.hostedemail.com (Postfix) with ESMTP id 026461C444D for ; Tue, 27 Oct 2026 15:16:10 +0000 (UTC) X-FDA: 85368756942.21.59154DD Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf26.hostedemail.com (Postfix) with ESMTP id 22FE914000D for ; Tue, 27 Oct 2026 15:16:08 +0000 (UTC) Authentication-Results: imf26.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=BuxeSr53; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf26.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1793114169; 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=WyoOBEMd5hZXCT3U6GbGErLU5iMuF52Y0APEdOL8vu8=; b=cyFU2MHruS73Ud4L7NqdfgjrQCQOnNXyFRXpozq1h7CBU+sQxv1f13r+aTBUkPVJ0OFqmD +PJsPLB4h5yWy5/1m03gQBDT0gSYAgEaPCGM/S8Fxuul1BYb6k+M7wTaNk/pc0ROY81yeD Az72yuRAWvD7edoXp0M6BK9iwzNm7eE= ARC-Authentication-Results: i=1; imf26.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=BuxeSr53; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf26.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1793114169; b=2AaMnapV4Yp9NN8xcOP6RJKqi9BWlGK8usUIpTRcTpBa6QxCJW8tFJEtO+azp2LzMTsWoE 2qMvbj3j3V6X1/H6jp4lO15maeoaogUgwx3CHovGhCV/P8cQquDeUjDMFiCLhMpL4fdOEv t8QCZYhU8A4lvlkIbrKBPifBe6nIYn4= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id 68F2942DF8; Tue, 27 Oct 2026 15:16:07 +0000 (UTC) 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-Archived-By: 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; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 22FE914000D X-Stat-Signature: jr6nbp3e6hy3i5joi83qpr5twi89fimk X-Rspamd-Server: rspam04 X-Spam-Status: No, score=-12.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS, USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=4.0.1 X-Rspam-User: X-HE-Tag: 1793114168-952519 X-HE-Meta: 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 r155UlMQ 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 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