From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B0C563BFE5A; Tue, 16 Jun 2026 18:25:42 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781634343; cv=none; b=DPoru3a/9mBGzo7IqP+GMcSoBNe7yWVlcux8BPZlfkGgPfWNGB7QAWNppxcQjs9Tnh3xivj7Q2p4NJ2dnylBryrgjcKvXuzzR4wDUfF+Xn0wS59UA9DQx1tn/YAbDFEAgDUu1aHp1ouWFrwY4XhQjbPgE4/A7pkjHjUPDvYYxv8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781634343; c=relaxed/simple; bh=X31JIQNPvjiIUmrfQRm9kD/dKaVouJ8ql/tskBSm04w=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=ltBvcpqsw6o1aBMR7Hp2x46njoj0PHEmImiYNRKfRXh7YQGgnzuEBxq9yp463qwVcaRphq1aHF8qMg3gbR6pmeLcDIKM30f4F5RxeZ/vjer1aIwGu5roURF2/MOjp+EI2CWcp24G2UP/4/bK7kutvCwKBjMeKRNu69IxAOu5/c8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=cv9Mixip; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="cv9Mixip" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9C8E31F000E9; Tue, 16 Jun 2026 18:25:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1781634342; bh=JSnTTFQdW3oo123/Lg9Zx/Aam1kbF4VkF+Neld2/+hM=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=cv9Mixip7u1PukJ0YK+aPJV4DVwOh7YeNPdUvP4yyJXHDdGRHUhVOL3PTrhU1YHfS Z8Gx3JO1R8fjs03htvkcA6rFmHUk3jgAn53I4ep4LEbORzuj6D45hcbECIwP3rUJcp PVokZl27OTaFvq4j2cUlntjPXCxvlK6v71N9Aeks= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, SeongJae Park , Fernand Sieber , Leonard Foerster , Shakeel Butt , Andrew Morton , Sasha Levin Subject: [PATCH 5.15 247/411] mm/damon/ops-common: call folio_test_lru() after folio_get() Date: Tue, 16 Jun 2026 20:28:05 +0530 Message-ID: <20260616145114.080876466@linuxfoundation.org> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260616145100.376842714@linuxfoundation.org> References: <20260616145100.376842714@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 5.15-stable review patch. If anyone has any objections, please let me know. ------------------ From: SeongJae Park [ Upstream commit d6b8b02a27b3dd09ec12144322b3dac46d9bc9ef ] damon_get_folio() speculatively calls folio_test_lru() before folio_try_get(). The folio can get freed and reallocated to a tail page. In the case, VM_BUG_ON_PGFLAGS() in const_folio_flags() can be triggered. Remove the speculative call. Also mark folio_test_lru() check right after folio_try_get() success as no more unlikely. The race should be rare. Also the problem can happen only if the kernel has enabled CONFIG_DEBUG_VM_PGFLAGS. No real world report of this issue has been made so far. This fix is based on only theoretical analysis. That said, a bug is a bug. A similar issue was also fixed via commit 3203b3ab0fcf ("mm/filemap: don't call folio_test_locked() without a reference in next_uptodate_folio()"). I don't expect this change will make a meaningful impact to DAMON performance in the real world, though I will be happy to be corrected from the real world reports. The issue was discovered [1] by Sashiko. Link: https://lore.kernel.org/20260525162256.8317-1-sj@kernel.org Link: https://lore.kernel.org/20260517234112.89245-1-sj@kernel.org [1] Fixes: 3f49584b262c ("mm/damon: implement primitives for the virtual memory address spaces") Signed-off-by: SeongJae Park Cc: Fernand Sieber Cc: Leonard Foerster Cc: Shakeel Butt Cc: # 5.15.x Signed-off-by: Andrew Morton Signed-off-by: Sasha Levin --- mm/damon/vaddr.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/mm/damon/vaddr.c b/mm/damon/vaddr.c index 6d8036671e60e5..dbb0f0fb2e598c 100644 --- a/mm/damon/vaddr.c +++ b/mm/damon/vaddr.c @@ -383,10 +383,10 @@ static struct page *damon_get_page(unsigned long pfn) { struct page *page = pfn_to_online_page(pfn); - if (!page || !PageLRU(page) || !get_page_unless_zero(page)) + if (!page || !get_page_unless_zero(page)) return NULL; - if (unlikely(!PageLRU(page))) { + if (!PageLRU(page)) { put_page(page); page = NULL; } -- 2.53.0