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=1793056862; b=f5nCz1amnKC2rARsMIwpyD71pa3e8VlhsO/XEydqMOLyFdTqVJ9Sqc12PSfJ6G8fHANQ 9aNzKfLjT0OfBbayoECIhWVbgRtppBj6OGw2fiTj6/zW8ejd0fyyfVpdQDb/xqHKD1sRq djnxEi/wE+cRVXZlYCSNP46y8f/tjOPZB7Fh6paryQq2jE6lrVbr6gIzdclsNMB/DvmPU Pbgj7Ttb335SP371Sv2LTm+yckhL9dcPcaMmTiMc7lyZckJqB15ZsJp8cJ/DNb9fFuTwB v+l0ekTUAdTISYwXqoW/jxCyDuzaO/krONHOwfNl2nO1LTBTLdjucwxq3c3aiO0/uBg== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793056862; h=Received:DKIM-Signature:From:Date:Subject:MIME-Version:Content-Type: Content-Transfer-Encoding:Message-Id:References:In-Reply-To:To:Cc: X-Mailer:X-Developer-Signature:X-Developer-Key; bh=A7gX/m+u4UMJmVyrb0f8N/TE7LE/A9ZKgusas0I4Rm4=; b=c9a/5pKj6hwu72xhzIGolXOsO5xJT25TCdVsWlffBvr7jL2K7vyeMfk1caBKaBEgWNBv khm/7EpzN5/0+Inb0feg/Zb9HCdRusBsMzdbZkg6i/aIa+DA8h8gZ9uJcknxJYQE2raAR EiC0KYcKEg5rFiNxVFu0Y961+pWzGjYPfp7DvtzJFUYVEDryHI8c5P7GxZr3jA1xS5u9K JFIqfn9GTegjcsAT3RDMw0+fr41uZi8bBDgzsSuSCqkYLXJ1Ez4nKnqW2YWhEnCalA9OP A5PBc0RVJaqVZ6Opl51QGv5t5uzkqBu5uLW0lHQrv5Qt0fARzVynzGQO/LZX/lTLrVw== 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=IQ31o5OD; 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 DCED1606A31A; Mon, 26 Oct 2026 23:21:01 +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=IQ31o5OD Received: by smtp.kernel.org (Postfix) with ESMTPSA id 787021F01829; Mon, 26 Oct 2026 23:20:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793056861; bh=A7gX/m+u4UMJmVyrb0f8N/TE7LE/A9ZKgusas0I4Rm4=; h=From:Date:Subject:References:In-Reply-To:To:Cc; b=IQ31o5ODFi1TCvdbW/Fvb4z47yUoIHd+cPWP+ynS5r1WhTWrbETdppp6UQPnNBNxh z31WeGR52qpW+2aGvMOZCs5WeWoxLP88gk4YFAygcZc4ACUUX8DD2shjSLjzIEH4ww m1+drTX7t/Pun8PbB7rJzwuns6/ninmkX9gfO2PwPlzwVjxssBxEQSKGnBVGupyQVY /ojkBuUvvCBPKQq4m1tQZnwUwQmb1uRNIn7es3b6LdJo5PDEmJVN+FqgnyDzSBqZfC JwiCAmYGedA2dLQJeDo2dtw5ETmwWJu0F1Chd28YsiHToKFXf9A+np6osHuygNVyd6 Ml1ekzN/YzLGw== From: "David Hildenbrand (Arm)" Date: Tue, 27 Oct 2026 00:17:30 +0100 Subject: [PATCH 10/46] mm/huge_memory: fix list corruption when deferred_split_scan() races with deferred_split_folio() 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 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20261027-fixes_core-v1-10-6f74bec9a5bb@kernel.org> References: <20261027-fixes_core-v1-0-6f74bec9a5bb@kernel.org> In-Reply-To: <20261027-fixes_core-v1-0-6f74bec9a5bb@kernel.org> To: Andrew Morton , Johannes Weiner , 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 Cc: 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 , "David Hildenbrand (Arm)" X-Mailer: b4 0.16.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=3458; i=david@kernel.org; h=from:subject:message-id; bh=r5BGBHRo9GSa/DI+t01ntFYVkxTFpvO09xLdXSpMdfA=; b=owGbwMvMwCF2/OVpCdfQ3ZWMp9WSGLLu35+idE7fMCKc/77ImbcKCVumnHE/1+sj9KHswaGDn hZPGvZc7ihlYRDjYJAVU2QJCr5v8PLlutpqNz5mmDmsTCBDGLg4BWAiHl8Z/octV9g4Uyis7u5F jiNybMWLTzh+1J55SfB7xavkONmzCfMYGRaeXdJmm+57kjNUJnZjr+fGhxucxVWlCw78WmCp27T wGxMA X-Developer-Key: i=david@kernel.org; a=openpgp; fpr=1BD9CAAD735C4C3A460DFCCA4DDE10F700FF835A 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) --- mm/huge_memory.c | 15 +++++++++++++-- 1 file changed, 13 insertions(+), 2 deletions(-) diff --git a/mm/huge_memory.c b/mm/huge_memory.c index bd44d58e86845..4c0194af9016d 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -4522,8 +4522,7 @@ int split_folio_to_list(struct folio *folio, struct list_head *list) * * It is unsafe to call folio_unqueue_deferred_split() until folio refcount is * zero: because even when the list_lru lock is held, a non-empty - * _deferred_list might be in use on deferred_split_scan()'s unlocked - * on-stack list. + * _deferred_list might be in use on deferred_split_scan()'s on-stack list. * * The list_lru sublist is determined by folio's memcg: it is therefore * important to unqueue deferred split before changing folio memcg. @@ -4665,10 +4664,22 @@ static unsigned long deferred_split_scan(struct shrinker *shrink, deferred_split_isolate, &dispose); list_for_each_entry_safe(folio, next, &dispose, _deferred_list) { + struct mem_cgroup *memcg; + struct list_lru_one *lru; bool did_split = false; bool underused = false; + /* + * Sync with deferred_split_folio(), which can requeue the + * folio once list_empty() is true, and sets PG_partially_mapped. + */ + rcu_read_lock(); + memcg = folio_memcg(folio); + lru = list_lru_lock_irq(&deferred_split_lru, folio_nid(folio), + &memcg); list_del_init(&folio->_deferred_list); + list_lru_unlock_irq(lru); + rcu_read_unlock(); if (!folio_test_partially_mapped(folio)) { /* -- 2.43.0