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Wed, 28 Oct 2026 10:41:14 +0000 X-Mizu-Trace-ID: b2f499d91e478fa4 X-Migadu-Flow: FLOW_OUT From: Lance Yang To: david@kernel.org Cc: akpm@linux-foundation.org, hannes@cmpxchg.org, mhocko@kernel.org, qi.zheng@linux.dev, shakeel.butt@linux.dev, ljs@kernel.org, kasong@tencent.com, baohua@kernel.org, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, baoquan.he@linux.dev, baolin.wang@linux.alibaba.com, liam@infradead.org, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, kees@kernel.org, peterz@infradead.org, jannh@google.com, pfalcato@suse.de, hughd@google.com, pasha.tatashin@soleen.com, pratyush@kernel.org, willy@infradead.org, jack@suse.cz, ziy@nvidia.com, lance.yang@linux.dev, riel@surriel.com, harry@kernel.org, apopple@nvidia.com, nico.pache@linux.dev, ryan.roberts@arm.com, dev.jain@arm.com, usama.arif@linux.dev, kas@kernel.org, matthew.brost@intel.com, jhubbard@nvidia.com, peterx@redhat.com, will@kernel.org, aneesh.kumar@kernel.org, npiggin@gmail.com, osalvador@suse.de, minchan@kernel.org, muchun.song@linux.dev, xu.xin@linux.dev, chengming.zhou@linux.dev, chrisl@kernel.org, shikemeng@huaweicloud.com, nphamcs@gmail.com, youngjun.park@lge.com, gourry@gourry.net, joshua.hahnjy@gmail.com, rakie.kim@sk.com, ying.huang@linux.alibaba.com, jgg@ziepe.ca, 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@toxicpanda.com Subject: Re: [PATCH 10/46] mm/huge_memory: fix list corruption when deferred_split_scan() races with deferred_split_folio() Date: Wed, 28 Oct 2026 18:41:07 +0800 Message-ID: <20261028104107.31470-1-lance.yang@linux.dev> X-Mailer: git-send-email 2.49.0 In-Reply-To: <20261027-fixes_core-v1-10-6f74bec9a5bb@kernel.org> References: <20261027-fixes_core-v1-10-6f74bec9a5bb@kernel.org> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 459AF100004 X-Stat-Signature: ehnse64iqdwwrcdc17e65p5abs4a8e1d X-Spam-Status: No, score=-13.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS, USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=4.0.1 X-Rspam-User: X-HE-Tag: 1793184076-734637 X-HE-Meta: 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 ZisFTkar jnHwuXid+64gEAJh/i25ekamsakYEg/r3NrE+rmrZZLODBnv4SgG0TwOv2ZlRn8yNzajHSx+4sMQ3GlqfL/1O7ltXRU4Ut/kdmiL+mHCI4NQfkF5GjDgAyHcgmXPxQxJmVShwglxTR3CQPO0XtnaqTJEt7nVbARMfO7wj206FtSwy5aA90BRknP4iiiqOKxMnOlpEn4wP9BXPL6tY8sQ3LyyPqgW+2qEg/T7H7lcnv8TrKh8RvJJ6ciSojHbz3W+gS0Lp4zNhS59QeL+TR0jT3htXRYxLpsoDEfk677AiVRroZsy3+bZ0vf8p3T0XgAwRw46x4aKhlrQZ9/T1jz/8qdxy6f6IXPdwkD5B1mnFVgWsaLKptVoChYbtx9w6C6ChQZQjHJblU0ABRiCwkOU1UDpT0gxM6Sqcb/cx0L81+I2Wftgn8TqYWnKbLBh38Drrg/04 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 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) >--- Nice work! Reviewed-by: Lance Yang