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=1794049352; b=PEkDwaKJdOD39XeEKNC7Gbi+WUCkg2SCEFKfxStcEcSY9a4px3x/62aaTHOMjkUx7awK 3m4gjAsEGZjG1OSvFvVoPcVkJmkQs/zISNFAv+ZEXeE10fTh1AZ8I5chA/0j5NgIt7vNP Mbh7uyH6t4ZohB1y//Cq45Rum98kQzKemcxjl3mhDhXwjeMqSsiacc/VL6Lwx5WyHPTq6 jO9+r74MS8KL0+K43HC22TQnDjJMvgyXZ+tFnOuTCeMrP0qV6MyNdzTo0/d1lW2HlQcj/ M1PgZK5qAQO6dS8e3BmzDRV4c1rXHYw7NCuKnN9s2mtHdJ5Tg2q8yzbRvjMubj4/BZg== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794049352; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: MIME-Version:Content-Type:Content-Transfer-Encoding; bh=4SnAU2JZkxXgp8tWSAaYg8SU4jRvBEGU84pWorYe2qk=; b=hagoVCRoUahTUAGYJIRv933WpqQu0YT/By+gMLj2i5kMcu6D5tR7G/kE1pxHJVJzdlut j1TOZoWM4HqcbFuYPTflwf3yISK/gQuxl079a4iHSp6eoB+pV0jxQFns4q0Pb7FPscLAB j5de6GMI/nLSX+o0hubACg/KKiQJPy+gZ4X3ajgLkTr/ra6AUCX1G+WD1MYvk+hp1XsRa eGZhTgQ5JH3zfT4jcwxi3Pdy/JgqUNXd6zZs0da8Dw0WRf087iXCI6dBhkipvHNUmG1OM XCJCVU9pjyjYxE7R3AHEncuD0SAk/pMx9KvWa9z2R83KSAcZMSDnm0GZVAU+JSTzUbA== 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=JE2ZNSjk; 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 6B52D606A326 for ; Sat, 7 Nov 2026 11:02:32 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=JE2ZNSjk Received: by smtp.kernel.org (Postfix) with ESMTPSA id 98EE71F0089F; Sat, 7 Nov 2026 11:02:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794049352; bh=4SnAU2JZkxXgp8tWSAaYg8SU4jRvBEGU84pWorYe2qk=; h=From:To:Cc:Subject:Date; b=JE2ZNSjkYYJl+ejR/YgtoerT9syjT1pnQYfZl3VEPrX4OHIKkvSotRVx5614QAfde x4bjms6i1RRMTkRYMVMm5Sew4HG5hgvxLneiflv/mKY4MGVbHEv3zsq8Oh44Iggigi wtJ5lUCVJjxLBgYVvL6C1icu+7a/gNEwp29FUH1USFBzeyjsXMMuB9JUfk10AYC6oU JINHaCBGKWhyDeU0KqvdyH/j9Rqtp27wLLwzPM8Y7oE39PMOhDkiCZCAS4iC75ghJg TR6R9plJrI7+pdrgpxdh0iu7frDwhfnHW3DFcTbOhmxZM8IYDcOvmLSmykG90dcqQg 9LkJUGI2l2Auw== From: Sasha Levin To: nicoyip.dev@gmail.com, akpm@linux-foundation.org, xu.xin16@zte.com.cn, david@kernel.org, hughd@google.com Cc: stable@vger.kernel.org Subject: FAILED: patch "[PATCH] mm/ksm: mark migration stores with WRITE_ONCE()" failed to apply to 5.15-stable tree Date: Sat, 7 Nov 2026 06:02:30 -0500 Message-ID: <20261107060230-failed-5.15-d3863210464f@kernel.org> X-Mailer: git-send-email 2.53.0 X-Mailing-List: stable@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: 8bit The patch below does not apply to the 5.15-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to . To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y git checkout FETCH_HEAD git cherry-pick -x d3863210464f69c18615cbe400d48a6e53e770d4 # git commit -s git send-email --to '' --in-reply-to '20261107060230-failed-5.15-d3863210464f@kernel.org' --subject-prefix 'PATCH 5.15.y' 'HEAD^..' Thanks, Sasha ------------------ original commit in Linus's tree ------------------ >From d3863210464f69c18615cbe400d48a6e53e770d4 Mon Sep 17 00:00:00 2001 From: Chengfeng Ye Date: Mon, 24 Aug 2026 19:24:33 +0800 Subject: [PATCH] mm/ksm: mark migration stores with WRITE_ONCE() ksm_get_folio() deliberately samples stable_node->kpfn and folio->mapping without taking the folio lock because the KSM folio may be migrated concurrently. folio_migrate_ksm() updates the same state using plain assignments. The reader can load the old kpfn, then the migrator can store the new kpfn, execute smp_wmb(), and clear the old folio's mapping before the reader checks that mapping. Thus the initial kpfn load can overlap its update and the subsequent mapping load can overlap the clear, with no common lock. This leaves marked READ_ONCE() accesses racing with plain stores. The kernel reported: BUG: KCSAN: data-race in folio_migrate_ksm / ksm_get_folio read (marked) to 0xffff8ce401421330 of 8 bytes by task 48 on cpu 3: ksm_get_folio+0x7f/0x2a0 ksm_scan_thread+0x1635/0x3330 kthread+0x1af/0x1f0 write to 0xffff8ce401421330 of 8 bytes by task 102 on cpu 1: folio_migrate_ksm+0x6a/0xd0 folio_migrate_flags+0x193/0x420 __migrate_folio.isra.0+0x162/0x1a0 migrate_folio+0x4c/0x70 move_to_new_folio+0xd6/0x170 Use WRITE_ONCE() for both stores to pair them with the existing lockless reads. This preserves the existing smp_wmb()/smp_rmb() migration protocol and control flow while preventing compiler transformations of the shared accesses. Link: https://lore.kernel.org/20260824112433.191301-1-nicoyip.dev@gmail.com Fixes: c8d6553b9580 ("ksm: make KSM page migration possible") Signed-off-by: Chengfeng Ye Signed-off-by: Andrew Morton Acked-by: Xu Xin Acked-by: David Hildenbrand (Arm) Cc: Hugh Dickins Cc: --- mm/ksm.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/mm/ksm.c b/mm/ksm.c index 49d48d1e09980..fe42c17490b89 100644 --- a/mm/ksm.c +++ b/mm/ksm.c @@ -1115,7 +1115,8 @@ static inline void folio_set_stable_node(struct folio *folio, struct ksm_stable_node *stable_node) { VM_WARN_ON_FOLIO(folio_test_anon(folio) && PageAnonExclusive(&folio->page), folio); - folio->mapping = (void *)((unsigned long)stable_node | FOLIO_MAPPING_KSM); + WRITE_ONCE(folio->mapping, + (void *)((unsigned long)stable_node | FOLIO_MAPPING_KSM)); } #ifdef CONFIG_SYSFS @@ -3316,7 +3317,7 @@ void folio_migrate_ksm(struct folio *newfolio, struct folio *folio) stable_node = folio_stable_node(folio); if (stable_node) { VM_BUG_ON_FOLIO(stable_node->kpfn != folio_pfn(folio), folio); - stable_node->kpfn = folio_pfn(newfolio); + WRITE_ONCE(stable_node->kpfn, folio_pfn(newfolio)); /* * newfolio->mapping was set in advance; now we need smp_wmb() * to make sure that the new stable_node->kpfn is visible -- 2.53.0